Tag: epidemiology

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

Who is Tom Frieden?

CDC Director Tom Frieden in West Africa during the Ebola epidemic.
CDC Director Tom Frieden in West Africa during the Ebola epidemic.

Thomas Frieden, MD, MPH has had a long career in public health, working as Commissioner of the New York City Health Department and most recently as the Director of the Centers for Disease Control and Prevention.

Dr Frieden went to Oberlin College, Columbia University College of Physicians and Surgeons, and did his residency in internal medicine at Yale University.

The field of public health aims to improve the health of as many people as possible as rapidly as possible.

A responsive government can maintain that people are responsible for their own health while also taking public health action that changes default choices to make it easier for people to stay healthy.

Dr. Frieden on The Future of Public Health

During his career, he:

  • worked to reduce rates of cases of multidrug-resistant tuberculosis by 80 percent in New York City
  • assisted the national tuberculosis control program in India
  • directed efforts to reduce smoking, including teen smoking, in New York City
  • led the response to the 2009 H1N1 flu pandemic in the US
  • has pushed for more funding to help control and treat Zika, which he says will likely “become endemic in this hemisphere”

Perhaps most importantly, and despite some criticism, Dr. Frieden led the CDC during the Ebola epidemic in West Africa. An epidemic that spread to the US and other countries and for which the “CDC has undertaken the most intensive outbreak response in the agency’s history.”

Recently, he has also highlighted “two shortcomings of our health system,” that the upward trend in life expectancy that we have seen over the past 50 years (about 9 years), “is neither as  rapid  as  it  should  be  —  we  lag  behind  dozens  of  other  nations – nor is it uniformly experienced by people in the United States.” And that is because “life  expectancy  and  other  key health outcomes vary greatly by race, sex, socioeconomic status, and geographic location.”

And after working to eliminate trans fats from restaurants in New York City and have chain restaurants post calorie information on their menu boards, he has continued to confront many of the more modern era epidemics, like obesity, hypertension, and diabetes.

He resigned from the CDC on January 20, 2017 and was replaced by Anne Schuchat, MD, who became the  became Acting Director.

For More Information on Thomas Frieden

Updated January 22, 2017

Save

This Year’s Flu Season

Breaking News: Flu season has started. (see below)

Flu activity continues to increase across the United States.
Flu activity continues to increase across the United States.

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.

Flu Facts

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

Among these flu facts include that:

  • there have been over 1,600 pediatric flu deaths since the 2003-04 flu season, including 110 flu deaths last year
  • about 113 kids 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

And even in a mild flu season, a lot of kids get sick with the flu.

This Year’s Flu Season

When does flu season start?

In general, flu season starts when you begin to see people around you with signs and symptoms of the flu, including fever, cough, sore throat, runny or stuffy nose, muscle or body aches, headaches, and fatigue, etc. To be more accurate, you can also look at reports for flu activity in your area, especially the weekly reports from the CDC. Those flu reports can also help you determine when flu season ends.

As of early December, the CDC again reported that “flu activity increased  slightly in the United States.”

Are we in store for an early flu season this year? It sure seems that way.

The CDC has also recently reported that:

  • seven states are already reporting widespread flu activity – Arkansas, Georgia, Louisiana, Massachusetts, Mississippi, Oklahoma, and Virginia
  • 18 states are now reporting regional flu activity  – Alabama, Alaska, Arizona, California, Colorado, Connecticut, Florida, Illinois, Kentucky, Maine, Missouri, New Hampshire, New York, North Dakota, Ohio, South Carolina, Texas, and Washington
  • 18 states are still reporting local flu activity – Hawaii, Idaho, Indiana, Kansas, Maryland, Michigan, Minnesota, Montana, Nebraska, New Jersey, New Mexico, North Carolina, Oregon, Pennsylvania, South Dakota, Tennessee, Wisconsin, and Wyoming
  • only 7 states are still reporting sporadic flu activity – Delaware, Iowa, Nevada, Rhode Island, Utah, Vermont, and West Virginia
  • no states have no flu activity anymore
  • between 151 to 166 million doses of flu vaccine will be available this year, including 130 million doses of thimerosal-free or preservative-free flu shots, so the great majority of flu shots will not contain mercury!
  • we still won’t have a nasal spray flu vaccine in the US this year, even though it is working well in other countries
  • although it is too early to tell how well the flu vaccine will work, it is good news that “The majority of the influenza viruses collected from the United States during October 1 through December 2, 2017 were characterized antigenically and genetically as being similar to the cell-grown reference viruses representing the 2017–18 Northern Hemisphere influenza vaccine viruses.”
  • there has already been seven pediatric flu deaths this year, including two new pediatric deaths this past week

Have you and your family gotten been vaccinated and protected against the flu yet?

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

CDC Influenza Situation Update

If not, this a great time to get a flu vaccine.

Recent Flu Seasons

Are H3N2 predominant flu seasons really worse than others?

  • 2003-04 flu season – 152 pediatric flu deaths (H3N2-predominant)
  • 2004-05 flu season – 47 pediatric flu deaths
  • 2005-06 flu season – 46 pediatric flu deaths
  • 2006-07 flu season – 77 pediatric flu deaths
  • 2007-08 flu season – 88 pediatric flu deaths (H3N2-predominant)
  • 2008-09 flu season – 137 pediatric flu deaths
  • 2009-10 flu season – 289 pediatric flu deaths (swine flu pandemic)
  • 2010-11 flu season – 123 pediatric flu deaths
  • 2011-12 flu season – 37 pediatric flu deaths
  • 2012-13 flu season – 171 pediatric flu deaths (H3N2-predominant)
  • 2013-14 flu season – 111 pediatric flu deaths
  • 2014-15 flu season – 148 pediatric flu deaths (H3N2-predominant)
  • 2015-16 flu season – 92 pediatric flu deaths
  • 2016-17 flu season – 110 pediatric flu deaths (H3N2-predominant)

In addition to high levels of pediatric flu deaths, the CDC reports that the four flu seasons that were H3N2-predominant in recent years were “the four seasons with the highest flu-associated mortality levels in the past decade.”

For More Information on the 2017-18 Flu Season

Updated December 10, 2017

Save

Save

Save

Save

Save

Save

Save

Efficacy vs Effectiveness of Vaccines

According to the CDC:

Vaccine efficacy and vaccine effectiveness measure the proportionate reduction in cases among vaccinated persons.

But what’s the difference between vaccine efficacy and effectiveness?

Vaccine efficacy is used when a study is carried out under ideal conditions, for example, during a clinical trial.

Vaccine effectiveness is used when a study is carried out under typical field (that is, less than perfectly controlled) conditions.

Postlicensure studies can often help figure out vaccine effectiveness. For example, the study “Varicella Vaccine Effectiveness in the US Vaccination Program: A Review,” that appeared in The Journal of Infectious Diseases in 2008 “reviewed the results of postlicensure studies of varicella vaccine effectiveness and compared these results with those of prelicensure efficacy trials.”

That study of the chicken pox vaccine found that “the estimates of effectiveness are lower than the prelicensure efficacy,” although several studies found the vaccine “100% effective in preventing combined moderate and severe varicella.”

For More Information On Efficacy vs Effectiveness of Vaccines: