Tag: epidemiology

What Happens When You Research the Disease?

We know how anti-vaccine folks think.

Anti-vaccine math…

And now we know how they do their research

How Anti-Vaccine Folks Research Disease

If you’re like me, you are probably wondering why they picked 2016 as the year to research.

Why look just at 2016?

And, there you see it.

In the past 6 years, 2016 was the year with the fewest cases of measles. Why not choose 2017 or 2018 to do their research?

But let’s look at 2016, even though the information isn’t complete:

  • 86 cases
  • cases in 19 states, including Alabama, Arizona, California, Colorado, Connecticut, Florida, Georgia, Hawaii, Illinois, Massachusetts, Michigan, Minnesota, New York, North Carolina, Oregon, Tennessee, Texas, and Utah
  • a large outbreak in Arizona (31 cases) linked to a private detention center and all that is known is that 7 of 9 staff members who got measles had received at least one dose of MMR, and 3 had received their dose very recently
  • a large outbreak in Shelby County, Tennessee, at least 7 cases, including 6 unvaccinated and one partially vaccinated child
  • a large measles outbreak (17 cases) in Los Angeles County and Santa Barbara County that was linked to the Los Angeles Orthodox Jewish community
  • two cases in Colorado, including an unvaccinated toddler and an unvaccinated adult – outbreaks which cost at least $68,192 to control

And of th cases in 2016, it seems that just 16% were vaccinated.

What about the claim that 26% were vaccinated?

That wasn’t 26% of the total number of cases, but rather 26% of the cases among US residents.

So if you do the math, that’s just 14 cases that were vaccinated, and out of 86 cases, that’s really just 16%. And a lot of those cases are skewed by the one outbreak at the detention center, in which they may have only received one dose of MMR and nearly half may have gotten vaccinated after the caught had already started!

What about the claim that “the odds of dying from the measles are like 0.00000013%” using numbers “before the vaccine was introduced in 1963?”

“Before a vaccine became available in 1963, measles was a rite of passage among American children. A red rash would spread over their bodies. They would develop a high fever. Severe cases could cause blindness or brain damage, or even death.”

CDC says measles almost eliminated in U.S.

In the pre-vaccine era, your odds of getting measles were very high. Remember, everyone eventually got measles.

And looking at statistics of reported measles cases and reported measles deaths, we know that death occurred in about 1 to 3 in every 1,000 reported cases.

So everyone got measles, but not everyone survived having measles.

Even if you use a more liberal count of 1 death in 10,000 cases, when all kids get measles, that’s a lot of deaths. Remember, about 450 people used to die with measles each year.

What about your odds of dying with measles now?

If you are fully vaccinated, then they are extremely low.

They are pretty low if you are unvaccinated too, in most cases, because you are benefiting from herd immunity and the fact that most folks around you are vaccinated, reducing your risk of being exposed to measles. Still, the risk is much higher than most anti-vaccine folks expect, because they often make the mistake of using the entire population of the United States in their calculations. They should instead just use the folks who are unvaccinated and susceptible, a much smaller number.

Want to increase your risk?

  • travel out of the country
  • hang out in a cluster with other unvaccinated people
  • stay unvaccinated

The odds aren’t in your favor to avoid measles if you are unvaccinated. Eventually, your luck might run out.

Starting to see the mistakes anti-vaccine folks make when they say they have done their research?

“How do they know how many people would have gotten measles and how many of them would have died?!?”

It’s not rocket science.

It’s epidemiology.

“We constructed a state-space model with population and immunisation coverage estimates and reported surveillance data to estimate annual national measles cases, distributed across age classes. We estimated deaths by applying age-specific and country-specific case-fatality ratios to estimated cases in each age-country class.”

Simons et al on Assessment of the 2010 global measles mortality reduction goal: results from a model of surveillance data.

Unfortunately, after years of improvements, measles deaths increased in 2017. And they will continue to increase, as our risk of getting measles continues to increase if folks don’t get vaccinated and protected.

Lastly, why does it “sound like millions of people would have died without the measles vaccine?”

Maybe because millions of people died in previous years, before they were vaccinated and protected.

Indeed, do your research, but you will find that vaccine-preventable diseases aren’t as mild as anti-vaccine folks believe. That’s why it is important to get vaccinated and protected.

More on Researching Vaccine-Preventable Disease

Were More Than Half of the Kids with Severe or Fatal Influenza in California Last Year Vaccinated?

We know that the flu is deadly and that most kids who die with the flu aren’t vaccinated.

Would it be news to anyone if Bob Sears was pushing misinformation about pediatric flu deaths in California?
Would it be news to anyone if Bob Sears was pushing misinformation about pediatric flu deaths in California?

That’s likely why some folks might have been surprised when Dr. Bob Sears said that “half of the patients admitted to ICUs for severe or (eventually) fatal cases of influenza last year were vaccinated.”

He seemed to be citing a news report from the California Department of Public Health.

Were More Than Half of the Kids with Severe or Fatal Influenza in California Last Year Vaccinated?

So what did the report from CDPH actually say?

“Influenza vaccination information was available for 455 (47.8%) of the 952 adult cases reported with severe or fatal influenza; 211 (46.4%) received the 2017–2018 influenza vaccine. One hundred twenty (64.2%) of the 187 reported pediatric cases >6 months of age had influenza vaccination information available; 61 (50.8%) received the 2017–2018 influenza vaccine.”

Influenza Surveillance Report 2017–2018 Season

When you do the math, you quickly see that only 61 of 187 kids, or 33% of the pediatric patients were known to be vaccinated.

The numbers are even lower for adults with severe or fatal flu – only 211 of 952 adults, or 22% were known to be vaccinated.

Melissa Floyd does not seem to understand basic epidemiology.
Melissa Floyd does not seem to understand basic epidemiology.

So the majority of kids and adults were either unvaccinated or their vaccination status was unknown. While an unknown vaccinated status doesn’t mean that they weren’t actually vaccinated, it certainly doesn’t mean that they were.

What about the idea that these vaccinated patients would “eventually” turn into fatal cases, as Dr. Bob posted?

Although there were 18 fatal pediatric flu cases in California during the 2017-18 flu season, and that is more than any of us want to see, it should be clear, with 194 non-fatal ICU cases, that most severe cases weren’t eventually fatal.

Hopefully it isn’t a newsflash to anyone that most kids who die with the flu aren’t vaccinated.

More on Flu Deaths in California

The 2018-19 Flu Season Update

Breaking News: Flu season continues, with widespread flu activity in most of the United States. (see below)

Flu activity is still rising…
Flu activity is still rising…

While flu season typically peaks in February, it is very important to understand that there are few things that are typical about the flu.

Since 1982, while we have been twice as likely to see a flu activity peak in February than other winter months, we have been just as likely to get that peak in December, January, or March. That makes it important to get your flu vaccine as soon as you can.

You really never know if it is going to be an early, average, or late flu season. That’s why it is best to not try and time your flu vaccine and to just get it as soon as you can.

Flu Season Facts

There will likely be some surprises this flu season – there always are – but there are some things that you can unfortunately count on.

Among these flu facts include that:

  • there have been over 1,660 pediatric flu deaths since the 2003-04 flu season, including 185 flu deaths last year
  • of the average 118 kids that die of the flu each year – most of them unvaccinated
  • antiviral flu medicines, such as Tamiflu, while recommended to treat high-risk people, including kids under 2 to 5 years of age, have very modest benefits at best (they don’t do all that much, are expensive, don’t taste good, and can have side effects, etc.)
  • a flu vaccine is the best way to decrease your child’s chances of getting the flu
  • FluMist, the nasal spray flu vaccine, is once again available for healthy kids who are at least 2-years-old

You can also count on the fact that even in a mild flu season, a lot of kids get sick with the flu.

What about reports that the flu shot won’t be effective?

Don’t believe them. The flu vaccine works and besides, it has many benefits beyond keeping you from getting the flu

This Year’s Flu Season

As of mid-February, the CDC reports that flu “seasonal influenza activity rose again over last week.”

The CDC has also recently reported that:

  • 48 states, Alabama, Alaska, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Florida, Georgia, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, Montana, Nebraska, Nevada, New Hampshire, New Jersey, New Mexico, New York, North Carolina, North Dakota, Ohio, Oklahoma, Oregon, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Utah, Vermont, Virginia, Washington, Wisconsin and Wyoming), are now reporting widespread flu activity (same as last week)
  • 1 states, West Virginia (same as last week)
  • only the District of Columbia is still reporting local flu activity (down from 3 last week)
  • only 1 state, Hawaii, and the U.S. Virgin Islands are still reporting sporadic flu activity (same as last week)
  • no states are still reporting no flu activity
  • the proportion of people seeing their health care provider for influenza-like illness (ILI) was 5.1% (up from 4.8% last week), which is still above the national baseline of 2.2%, but far below the 7.5% we saw last year
  • The overall hospitalization rate was 7.4 per 100,000 population. The highest rate of hospitalization was among adults aged ≥65 (64.1 per 100,000 population), followed by children aged 0-4 (36.8 per 100,000 population) and adults aged 50-64 (32.5 per 100,000 population).
  • there have already been 41 pediatric flu deaths this year, including 7 new deaths this past week

Some good news?

So far, influenza A(H1N1)pdm09 viruses are most common (that’s good, because H3N2 years are typically more severe), and the “majority of influenza viruses characterized antigenically and genetically are similar to the cell-grown reference viruses representing the 2018–2019 Northern Hemisphere influenza vaccine viruses..”

And the interim estimates of flu season effectiveness are fairly good, with an overall vaccine effectiveness of 61% in children and teens.

Are you going to get your kids a flu vaccine this year?

“CDC recommends that everyone 6 months and older get a  flu vaccine as soon as possible.”

CDC Influenza Situation Update

Although flu season has started, it is definitely not too late to get a flu vaccine.

For More Information on the 2018-19 Flu Season

Updated February 25, 2019

Save

Save

Save

Save

Save

Save

Save

How Do They Figure out Who Starts an Outbreak?

As we continue to see outbreaks of vaccine-preventable diseases in the post-vaccination era, it is important that these outbreaks be quickly contained.

But it is important to understand that these outbreaks don’t simply stop on there own. A lot of work goes into containing them.

Working to Contain an Outbreak

And that work containing outbreaks is expensive. Much more expensive than simply getting vaccinated.

For example, the total personnel time and total direct cost to the New York City Department of Health and Mental Hygiene responding to and controlling the 2013 outbreak in NYC were calculated to be at least $394,448 and 10,054 personnel hours.

Why it is so expensive is easy to see once you understand all of the work that goes into containing an outbreak. Work that is done by your local health department as soon as a case of measles, or other vaccine-preventable disease, is suspected.

Work that, for a measles outbreak for example, includes:

  • initiating a case and contact investigation
  • quickly confirming that the patient actually has measles, including testing
  • assessing the potential for further spread – identifying contacts who aren’t immune to measles and are at risk for getting measles
  • isolating people with measles and quarantining contacts who aren’t immune to measles for at least 21 days after the start of the measles rash in the last case of measles in the area, including everyone who is intentionally unvaccinated
  • offering postexposure vaccination, a dose of the MMR vaccine within 72 hours of exposure to contacts who are not fully immune so that they can get some protection maybe don’t have to be quarantined
  • having targeted immunization clinics in the affected population, such as a school or church, to get as many people vaccinated as possible, even after 72 hours, so they have can be protected in the future

That’s an awful lot of work.

Work that continues until the outbreak officially ends.

Finding the Source of an Outbreak

Another big part of the work that goes on to contain an outbreak is identifying the source of the outbreak.

Was it someone who had recently been traveling overseas, a visitor from out of the country, or someone that was already part of an another outbreak?

Why is that so important?

If you don’t find the source of the outbreak, then you can’t be sure that you have found all of the people that have been exposed, and the outbreak might go on for an extended period of time.

And no, it is never shedding, a vaccine strain, or a recently vaccinated child that causes these measles outbreaks.

Anatomy of a Measles Outbreak

A closer look at the measles outbreak in San Diego, California in 2008 can help folks understand even better what happens during one of these outbreaks.

A 7-year-old who is unvaccinated because his parents have a personal belief vaccine exemption travels to Switzerland with his family.

A week after returning home from the trip, he gets sick, but returns to school after a few days. He then develops a rash and sees his family physician, followed by his pediatrician, and then makes a trip to the emergency room because he continues to have a high fever and rash (classic measles symptoms).

He is eventually diagnosed with measles, but not before eleven other children are infected with measles. This includes two of his siblings, five children in his school, and four children who were exposed at his pediatrician’s office.

It is not as simple as that though.

During this measles outbreak:

  • Three of the children who became infected were younger than 12 months of age, and were therefore too young to have been vaccinated
  • Eight of the nine children who were at least 12 months old were intentionally unvaccinated because they also had personal belief vaccine exemptions
  • About 70 children were placed under voluntary quarantine for 21 days after their last exposure because they were exposed to one of the measles cases and either didn’t want to be vaccinated or were too young
  • One of the infants with measles traveled to Hawaii, raising fears that the measles outbreak could spread there too

All together, 839 people were exposed to the measles virus.

This family didn't have a choice about their son getting sick - he was too young to be vaccinated when he was exposed to an unvaccinated child with measles.
This family didn’t have a choice about their son getting sick – he was too young to be vaccinated when he was exposed to an unvaccinated child with measles.

At least one of them was a 10-month-old infant who got infected at his well child checkup, was too young to have gotten the MMR vaccine yet, and ended up spending three days in the hospital – time his parents spent “fearing we might lose our baby boy.”

The parents of this 10-month-old weren’t looking for a vaccine exemption and didn’t want their child to catch measles, a life-threatening, vaccine-preventable disease. Instead, they were counting on herd immunity to protect him until their child could be protected with an MMR vaccine. They were one of “those who come into contact with them” that got caught up in a decision of some other parents to not vaccinate their child.

The kids who are at risk and get a vaccine-preventable disease because they are too young to get vaccinated, have an immune system problem that prevents them from getting immunized or their vaccine from working, and the kids who simply didn’t get protected from a vaccine are the hidden costs of these measles outbreaks that we don’t hear about often enough.

What to Know About Finding the Source of an Outbreak

Without all of the hard work that goes into containing outbreaks, the outbreaks of measles, pertussis, mumps, hepatitis A, and other vaccine preventable diseases would be even bigger.

More on Finding the Source of an Outbreak

 

Who is Alexander Langmuir?

Alexander Langmuir is typically described as a hero or titan of public health.

Then why do some folks think he was against the flu and measles vaccines?

Who is Alexander Langmuir?

Dr. Alexander Langmuir has been called the father of infectious disease epidemiology.

Why?

In 1949, he established the CDC’s Epidemiology Program. Actually, at the time, the CDC was still called the Communicable Disease Center.

Dr. Alexander Langmuir and his Polio Surveillance Unit at the EIS in 1955.
Dr. Alexander Langmuir and his Polio Surveillance Unit at the EIS in 1955.

Dr. Langmuir, as Chief Epidemiologist at CDC for 21 years, also:

  • founded the Epidemic Intelligence Service (EIS)
  • instituted a malaria surveillance system
  • established national disease surveillance system for the United States
  • was involved in resolving the Cutter incident
  • brought the Morbidity and Mortality Weekly Report to CDC
  • investigated the swine influenza virus vaccine incident, when it was thought that some people developed GBS after getting the new swine flu vaccine in 1976

His work saved the lives of hundreds of thousands of people.

Don't believe any propaganda or quotes without sources attributed to Alexander Langmuir.
Don’t believe any propaganda or quotes without sources attributed to Dr. Alexander Langmuir.

Did he ever tell folks to not get a flu shot?

Was he ever concerned about mercury in flu shots?

Considering that Dr. Langmuir died in 1993, before folks became concerned about thimerosal in vaccines, that’s unlikely. That’s especially so considering that the only place you can find these types of quotes are on anti-vaccine websites.

Still, Langmuir was critical of flu shots.

“From this appraisal of the experience in the past three and one-half years, it is apparent that progress in the control of influenza has not been impressive.”

Langmuir et al. on The Epidemiological Basis For The Control Of Influenza

He didn’t think that they worked well enough. Or more importantly, he didn’t think we had enough information about how well they worked.

“Our information regarding the occurrence of influenza is largely qualitative. Schools close, absenteeism increases, medical services become taxed, virus isolations and serological identifications are made in great numbers, and daily accounts appear in our newspapers and on television. We know we have an epidemic and we know its specific cause, but we have few quantitative measures of incidence, age- and sex-specific attack rates, and character and severity of complications. Further- more, we have only crude data regarding mortality. We do not know what proportion of excess deaths occurs among reasonably active and productive citizens in contrast to deaths among persons who are already invalids suffering from severely debilitating pre-existing disease. Despite this serious deficiency we base our recommendations for vaccine use largely on mortality experience. We undertake major efforts to produce influenza vaccine in large amounts, but we have no meaningful information regarding its actual distribution. We do not know to what extent it actually reaches persons at highest risk.”

Langmuir et al. on A Critical Evaluation of Influenza Surveillance

But he wasn’t anti-vaccine.

And he never said that flu shots weren’t safe.

“The availability of potent and effective measles vaccines, which have been tested extensively over the past 4 years, provides the basis for the eradication of measles in any community that will raise its immune thresholds to readily attainable levels.”

Langmuir et al. on Epidemiologic Basis For Eradication Of Measles In 1967

And concerning all that he did in the field of public health, he is certainly not someone that anti-vaccine folks should be quoting.

More on Alexander Langmuir

Do More Vaccinated or Unvaccinated Kids Get Sick in Outbreaks?

Some anti-vaccine folks continue to claim that vaccines don’t work and that most outbreaks of vaccine-preventable diseases are actually caused by kids who have been vaccinated.

They also push the myth that more vaccinated than unvaccinated kids get sick in most outbreaks.

Vaccinated vs Unvaccinated in an Outbreak

So are outbreaks usually caused by kids who have been vaccinated?

No, of course not.

Do we sometimes see more vaccinated than unvaccinated kids in some of these outbreaks?

Yes, sometimes we do.

Vaccine Epidemiology

Wait, what?

Yes, we sometimes see more vaccinated than unvaccinated kids in an outbreak.

How can that be if vaccines work?

It is actually very easy to understand once you learn a little math and a little more epidemiology.

Basically, it is because while vaccines work, they don’t work 100% of the time, and more importantly, there are way more vaccinated kids around than unvaccinated kids.

The Mathematics of Disease Outbreaks

That means that you need to understand that more than the absolute number of vaccinated and unvaccinated people that got sick in an outbreak, you really want to know the percentages of vaccinated vs unvaccinated kids who got sick.

For example, in a school with 1,000 kids, you might be very surprised if six kids got a vaccine preventable disease, and three of them were vaccinated, leaving three unvaccinated.

Does that really mean that equal amounts of vaccinated and unvaccinated kids got sick?

I guess technically, but in the practical sense, it only would if half of the kids in the school were unvaccinated. Now unless they go to a Waldorf school, it is much more likely that over 90 to 95% of the kids were vaccinated, in which case, a much higher percentage of unvaccinated kids got sick.

Before we use a real world example, some terms to understand include:

  • attack rate – how many people will get sick when exposed to a disease
  • basic reproductive number or Ro – different for each disease, Ro basically tells you  just how contagious a disease is and ranges from about 1.5 for flu, 8 for chicken pox, and 15 for measles
  • vaccine coverage – how many people are vaccinated
  • vaccine efficacy – how well a vaccine works

You also need to know some formulas:

  • attack rate = new cases/total in group
  • vaccine coverage rate = number of people who are fully vaccinated / number of people who are eligible to be vaccinated
  • vaccine effectiveness = (attack rate in unvaccinated group – attack rate in vaccinated group) / attack rate in unvaccinated group x 100

Unfortunately, it is often hard to use these formulas in most outbreaks.

Why?

For one thing, it is hard to get accurate information on the vaccination status of all of the people in the outbreak. In addition to those who are confirmed to be vaccinated or unvaccinated, there is often a large number who’s vaccination status is unknown. And even if you know the vaccination status of everyone in the outbreak, it can be even harder to get the vaccine coverage rate or a neighborhood or city.

Outbreaks of Vaccine Preventable Diseases

Reports of measles outbreaks among highly vaccinated populations are from before we started doing a second dose in 1994.
Reports of measles outbreaks among highly vaccinated populations are from before we started doing a second dose of MMR… way back in 1994.

We know what starts most outbreaks.

And no, it’s not shedding

For example, with measles, it is typically an unvaccinated person who travels out of the country, returns home after they have been exposed but are still in their incubation period, and then exposes others once they get sick. And the great majority of folks in these measles outbreaks are unvaccinated.

Some examples of these outbreaks include:

  • the 2014 Ohio measles outbreak that started with two unvaccinated Amish men getting measles in the Philippines while on a missionary trip and ended up with at least 388 cases before it was over, almost all unvaccinated
  • a 2013 North Carolina measles outbreak with 22 cases started after an unvaccinated traveler had returned from India
  • an outbreak of measles in New York, in 2013, with at least 58 cases, tarted with an intentionally unvaccinated teen returning from a trip to London
  • a 2011 outbreak of measles in Minnesota, when an unvaccinated child traveled out of the country, developed measles, and returned to his undervaccinated community, causing the state’s largest measles outbreak in 20 years

But what about mumps and pertussis?

Those outbreaks are all among vaccinated kids, right?

Nope.

In one of the biggest mumps outbreak, in Arkansas, only 71% of people were up-to-date on their vaccines!

And keep in mind that while we do know that there are issues with waning immunity with some vaccines, you are still much more likely to become infected and get others sick if you are not vaccinated. And you will likely have a much more severe disease.

A 2013 pertussis outbreak in Florida is a good example that even with all the bad press it gets, the DTaP and Tdap vaccines work too. This outbreak was started by an unvaccinated child at a charter school with high rates of unvaccinated kids. About 30% of unvaccinated kids got sick, while there was only one case “in a person who reported having received any vaccination against pertussis.”

In another 2013 pertussis outbreak in Florida, this time in a preschool, although most of the kids were vaccinated, the outbreak started with “a 1-year-old vaccine-exempt preschool student.” And the classroom with the highest attack rate, was “one in which a teacher with a laboratory-confirmed case of pertussis who had not received a Tdap booster vaccination, worked throughout her illness.”

In outbreak after outbreak, we see the same thing, sometimes with deadly consequences – an unvaccinated child or adult triggers an outbreak and then a lot of unvaccinated folks get sick. Unfortunately, others get caught up in these outbreaks too, including those too young to be vaccinated, those who can’t be vaccinated because of true medical exemptions, and those whose vaccines may not have worked as well as we would have liked.

Get educated.

Vaccines are safe. Vaccines are necessary. Vaccines work.

What to Know About Vaccinated vs Unvaccinated in Outbreaks

Most outbreaks are started by someone who is unvaccinated, often after a trip out of the country, and the resulting outbreak will likely get many more unvaccinated than vaccinated folks sick.

More About Vaccinated vs Unvaccinated in Outbreaks

Challenging the Concept of Herd Immunity

Before we talked about clusters of unvaccinated children, experts warned about pockets of susceptibles.
Before we talked about clusters of unvaccinated children, experts warned about pockets of susceptibles.

The idea of herd immunity has been around since at least 1923 and became used to describe “the indirect protection afforded to individuals by the presence and  proximity of others who are immune.”

That’s not much different from how the CDC defines herd immunity today:

A situation in which a sufficient proportion of a population is immune to an infectious disease (through vaccination and/or prior illness) to make its spread from person to person unlikely. Even individuals not vaccinated (such as newborns and those with chronic illnesses) are offered some protection because the disease has little opportunity to spread within the community.

Also called community immunity, it is often misunderstood by folks in the anti-vaccine movement.

Challenging the Concept of Herd Immunity

That the idea of herd immunity is being challenged is not new.

“Along with the growth of interest in herd immunity,  there has been a  proliferation of views of what it means or even of whether it exists at all.”

Paul E. M. Fine Herd Immunity: History, Theory, Practice

If you get educated about vaccines and understand how herd immunity works, it is easy to refute these challenges, especially the idea that herd immunity isn’t real just because we still have outbreaks of vaccine-preventable diseases among highly vaccinated communities.

Why do we still have outbreaks then?

It is mostly because we live in open communities that don’t mix randomly.

Keep in mind that the best model for herd immunity is a randomly mixing closed community – “one in which the probability of contact within any time interval is the same for every choice of two individuals in the population.”

Again, that doesn’t mean herd immunity doesn’t work.

It just means we can expect to see some outbreaks when someone in a well vaccinated community visits another community with lower vaccination levels and more disease, gets sick, and returns.

“However,  within the population of a community,  there may be pockets of  susceptibles, either because prior epidemics have failed to spread into the group or because they have not accepted immunization.”

John P. Fox Herd Immunity

You must also consider the size of the community when thinking about herd immunity, for example, a family, school, neighborhood, or city, versus the entire state. So you can have herd immunity levels of protection at the state or city level because of high average vaccination levels, but pockets of susceptibles who live in the same neighborhood or go to the same school can mean that you don’t have herd immunity in those places, leading to outbreaks.

“Hib vaccine coverage of less than 70% in the Gambia was sufficient to eliminate Hib disease, with similar findings seen in Navajo populations.”

RA Adegbola Elimination of Hib disease from The Gambia after…

Lastly, there is not one herd immunity level for all diseases. It is a separate threshold for each and every disease, depending on how easily it spreads, how many people are already immune, how long immunity lasts, if there is a vaccine, and the effectiveness of the vaccine, etc. That means that a community can have herd immunity for Hib and polio, but not the flu, and for rubella and measles, but not pertussis.

What happened in The Gambia is a great example of herd immunity. After introducing a three dose primary Hib immunization schedule (no booster dose), rates of Hib meningitis quickly went from 200 per 100,000 to none. A few years later, there were 6 cases of Hib meningitis in mostly vaccinated children (no booster dose) and in the majority of cases, “close contacts had a history of frequent or recent travel to Senegal, a neighboring country with strong kinship links with The Gambia and where vaccination against Hib was not introduced” until the following year.

With a Hib meningitis rate of 3 per 100,000, they are still far below pre-vaccine levels of disease, and their situation doesn’t mean that herd immunity isn’t real, as you will understand once you review these myths about herd immunity.

Myths About Herd Immunity

What are some common myths about herd immunity?

  • that natural immunity is better than getting vaccinated. Not True. Natural immunity often comes with a price. Remember, many vaccine-preventable diseases are life-threatening, even in this age of modern medicine.
  • you can just hide in the herd. Not True. “Freeloaders” can gamble and hope that their intentionally unvaccinated kids won’t get a vaccine-preventable disease, but it won’t always work. There is a risk to “free-riding, in which individuals profit from the protection provided by a well-vaccinated society without contributing to herd immunity themselves.”
  • most adults aren’t immune because they haven’t been vaccinated or don’t get boosters, but since we aren’t seeing that many outbreaks, herd immunity itself must be a myth. Not True. Adults were either born in the pre-vaccine era and likely have natural immunity or were born in the vaccine era and are vaccinated and immune. But again, herd immunity is disease specific, so when we talk about herd immunity for measles, it doesn’t matter if they have immunity against hepatitis A or Hib. And adults get few boosters or catch-up vaccines. Also, some vaccines, like Hib and Prevnar, have indirect effects, protecting adults even though they aren’t vaccinated because vaccinated kids are less likely to become infectious.
  • most vaccines wear off too soon to provide long lasting protection for herd immunity to be real. Not True. While waning immunity is a problem for a few diseases, like pertussis and mumps, and you need boosters for others, like tetanus, vaccine induced immunity is typically long lasting and often life-long.
  • herd immunity wasn’t developed by observing immunized people, it was all about natural immunity. Not True. The first experiments about herd immunity by Topley and Wilson in 1923 involved vaccinated mice. Ok, they weren’t immunized people, but it wasn’t just about natural immunity! And much earlier, in 1840, it was noted that “smallpox would be disturbed, and sometimes arrested, by vaccination, which protected a part of the population.” That’s herd immunity he was talking about.
  • herd immunity is not a scientifically validated concept. Not True. It has been well studied for almost 100 years.
  • if herd immunity was real, diseases would be eradicated once you reached herd immunity levels. Not True. Reaching herd immunity levels simply starts a downward trend in disease incidence. A little more work has to be done at the final stages of eradication, like was done for smallpox and is being done for polio.
  • natural immunity causes much of the decrease in mortality from a disease in the developed world, even before a vaccine is introduced. Not True. While it is certainly true that there was a big drop in mortality in the first half of the 20th century for most conditions because of improvements in sanitation, nutrition, and medical science, it was not a consequence of natural herd immunity. And we continue to see significant levels of mortality and morbidity for many diseases in the modern era, especially for those that can’t yet be prevented by a vaccine, like RSV, West Nile Virus, and malaria, etc.
  • vaccines aren’t 100% effective, so herd immunity can’t really work. Not True. Part of the equation to figure out the herd immunity threshold for a disease takes into account the effectiveness of a particular vaccine.
  • folks with medical exemptions for vaccines put the herd at risk just the same as those who intentionally skip vaccines. Not True. Children and adults with medical exemptions, including immune system problems, those getting treatments for cancer, and other true medical exemptions don’t have a choice about getting vaccinated.

So, like other anti-vaccine myths, none of the herd immunity myths you may have heard are true.

That makes it hard to understand why Dr. Russel Blaylock goes so far as to say “that vaccine-induced herd immunity is mostly myth can be proven quite simply.” Does he just not understand herd immunity? That is certainly a possibility, because “although herd immunity is crucial for the elimination of infectious diseases, its complexity and explicit relationship to health politics cause it to remain under-explained and under-used in vaccine advocacy. “

He is also really big into pushing the idea that adults have no or little immunity, because when he was in medical school, he was “taught that all of the childhood vaccines lasted a lifetime,” but it has now been discovered that “most of these vaccines lost their effectiveness 2 to 10 years after being given.”

The thing is, Blaylock graduated medical school in 1971, when the only vaccines that were routinely used were smallpox (routine use ended in 1972), DPT, OPV, and MMR (it had just become available as a combined vaccine in 1971). Of these, it was long known that smallpox, diphtheria, and tetanus didn’t “last a lifetime,” and the live vaccines OPV and MMR, except for the mumps component, actually do.

Blaylock, like most anti-vaccine folks who push myths about herd immunity, is plain wrong. And like most anti-vaccine myths, using herd immunity denialism to convince parents that it is okay to skip or delay vaccines puts us all at risk for disease.

What To Know About Herd Immunity Myths

Herd immunity is not junk science or a false theory. Herd immunity is real, it works, and explains how people in a community are protected from a disease when vaccination rates are above a certain threshold.

More About Herd Immunity Myths