Still, while quarantines are helpful to control disease outbreaks, they clearly aren’t enough. That’s evident by the way that vaccines were used in Leicester to control smallpox, even though some folks say it was all due to quarantines. It wasn’t.
Pertussis has been known since at least the Middle Ages, although the bacteria that causes pertussis, Bordetella pertussis, wasn’t discovered until 1906.
That discovery led to the later development of the first pertussis vaccines, but before then, pertussis was a big killer, with epidemic cycles every 2 to 5 years.
During one of these cycles in the United States, from 1926 to 1930, there were:
909,705 cases, and
Unfortunately, even natural infection doesn’t provide life-long immunity, so adults would get pertussis and give it to susceptible kids, who were most likely to die during these epidemics.
But even in non-epidemic years, a lot of folks got pertussis. The number of reported cases ranged from “just” 161,799 in 1928 to 202,210 in 1926. And during one of the biggest years, 1934, there were 265,269 cases!
Post-Vaccine Era Pertussis Outbreaks
That changed in the vaccine era.
The first pertussis vaccines were developed in the 1930s and became more widely used in the 1940s when it was combined into the whole-cell DTP vaccine.
This was replaced with the acellular DTaP vaccine in 1997, with the Tdap vaccine being added to the vaccine schedule in 2006.
These vaccines helped to greatly reduce how many people got pertussis and how many people died from pertussis:
1940 – 183,866 cases
1950 – 120,718 cases and 1, 118 deaths
1960 – 14,809 cases and 118 deaths
1970 – 4,249 cases and 12 deaths
1980 – 1,730 cases and 11 deaths
1990 – 4,570 cases and 12 deaths
2000 – 7,867 cases and 12 deaths
2010 – 27,550 cases and 26 deaths
They never eradicated pertussis though, and as you can see, recently, pertussis cases have started to rise again.
In 2012, there were 48,277 cases of pertussis in the United States, the most since 1950, when we had 68,687 cases. Unfortunately, with the rise in cases, we are also seeing the tragic consequences of this disease – 20 deaths in 2012, mostly infants under age 3 months.
Pertussis cases remained steady, but high, in 2013 and 2014, at around 30,000 cases in the United States.
In California, pertussis reached epidemic levels. The California Department of Public Health reported at least 11,114 cases in 2014 – the highest numbers of pertussis cases in the state in 70 years!
And as expected with the rise in cases, there were 3 pertussis related deaths in California that year – all infants who had contracted pertussis when they were less than 8 weeks old. Two of the infants became sick in 2013, but the third, a 5-week-old baby, got infected in 2014.
Another baby, only 25 days old died in early 2015, but will be counted as the 2nd death of 2014 since that is when the illness started. About 383 patients, mostly infants who are less than 4 months old, were hospitalized in California that year, including 80 who required intensive care. And according to the California Department of Public Health, about 82% of the cases in infants were born to mothers who did not receive a dose of Tdap during their third trimester of pregnancy.
What’s happened since then?
Pertussis cases are continuing to fall each year! In fact, with about 16,000 cases in the United States, 2017 may have ended with the lowest number of pertussis cases since 2008.
Still, with just 1,830 pertussis cases in California in 2016, there were two deaths – both infants who were younger than 3 months of age when they got sick. And there was at least one death in 2017, with similar rates of disease, although reports are still preliminary.
Why So Many Pertussis Outbreaks?
Ever since a 2010 California pertussis outbreak, in which there were 9,154 cases of pertussis, the most in 63 years, and 10 infants died, many people, especially parents, began wondering why we were seeing more pertussis these days.
Is it because the pertussis vaccines simply don’t work, as the anti-vaccine movement would have you think?
A commentary, Why Do Pertussis Vaccines Fail?, by James Cherry, MD, gave us some answers.
While the title of the article might have you think that all of the blame lies with the pertussis vaccines, that certainly isn’t the case. While there can be vaccine failures with the pertussis vaccines, just like any other vaccine, that doesn’t mean that the vaccine doesn’t work for most children.
One of the problems is that the DTaP vaccine likely isn’t as effective as the older DTP vaccine. So instead of efficacy of 84 to 85%, as was once believed, it is likely closer to just 71 to 78%.
Other issues, including waning immunity, the possibility of an incorrect balance of antigens in the vaccine that could create a blocking effect, and genetic changes in the B. pertussis bacteria, could also possibly lead to increased vaccine failure rates.
So it isn’t that the pertussis vaccines don’t work.
That should be easy to see when you look at the pertussis rates in California, when the highest rates by far were in infants less than 6 months of age (434 per 100,000 people). In contrast, children who were 6 months to 6 years old had a rate of only 62 per 100,000.
And the results of a study that were presented at the 49th annual meeting of the Infectious Diseases Society of America in Boston show just how important the pertussis vaccine is, as:
vaccine effectiveness was 98.1 percent among children who received their 5th dose within the past year
long term effectiveness – children who were five or more years past their last DTaP dose – was about 71 percent
children who had never received any doses of DTaP (unvaccinated children) faced odds of having whooping cough at least eight times higher than children who received all five doses
It is also important to note that the high rates seen in 2010 in California are still well below the rates that were seen in the pre-vaccination era, when the attack rate of pertussis in the United States was as high as 157 per 100,000 people, with about 200,000 cases a year.
What’s the answer?
“The present “resurgence of pertussis” is mainly due to greater awareness and the use of PCR for diagnosis. There are also many other factors which have contributed to the “resurgence.” New vaccines are clearly needed; with our present vaccines (DTaP and adolescent and adult formulated tetanus and diphtheria toxoids and acellular pertussis vaccine (Tdap)), if used correctly, severe pertussis and deaths in infants can be prevented.”
James D. Cherry, MD on The History of Pertussis (Whooping Cough); 1906 – 2015: Facts, Myths, and Misconceptions
It certainly isn’t for more kids to follow non-standard, parent-selected, delayed protection vaccine schedules or to simply skip vaccines all together. Since natural immunity isn’t going to keep newborns and infants from getting pertussis, the ages which are most at risk for life-threatening infections, they can catch pertussis from people around them, including those working on their natural immunity. Natural infections don’t even provide life-long protection against pertussis, as some people believe. That natural immunity wanes fairly quickly too.
The future of pertussis control is more likely going to be in maximizing our current vaccination program, including getting more teens and adults to get the Tdap vaccine, especially when women are pregnant.
That’s the best strategy, at least until new pertussis vaccines are developed. It provides a lot of benefits. According to the CDC, like with the flu vaccine, when you get a pertussis vaccine, in addition to protecting yourself and those people around you, “people who do catch whooping cough after being vaccinated are much less likely to be hospitalized or die from the disease.”
Unfortunately, not everyone has gotten the message. And because of waning immunity, children who aren’t vaccinated against pertussis can’t “hide in the herd” and rely on the rest of us who do vaccinate our children to provide them with protection. Instead, since they are at a higher risk, they get pertussis and get even more people sick.
In one study, Parental refusal of pertussis vaccination is associated with an increased risk of pertussis infection in children, researchers found that “vaccine refusers had a 23-fold increased risk for pertussis when compared with vaccine acceptors, and 11% of pertussis cases in the entire study population were attributed to vaccine refusal.” The highly contagious nature of pertussis then means every primary case is probably going to infect as many as 17 other people. That’s why it makes sense that higher rates of children using vaccine exemptions could be at least one of the factors in these outbreaks.
In fact, several studies, including, Geographic Clustering of Nonmedical Exemptions to School Immunization Requirements and Associations With Geographic Clustering of Pertussis, found that “geographic pockets of vaccine refusal are associated with the risk of pertussis outbreaks in the whole community.”
Many factors are responsible for the rise in pertussis outbreaks in recent years, but it is clear that being unvaccinated and unprotected put you at greatest risk for getting pertussis and passing it on to others.
Not surprisingly, there are no benefits to skipping or delaying your child’s vaccines, but there are plenty of risks.
What Are the Risks of Delaying Vaccines?
Of course, the biggest risk of delaying your child’s vaccines is that they will get a disease that they could have been vaccinated and protected against.
“In 1989, the Haemophilus influenzae type b vaccine was relatively new and not yet routine. I was aware of the vaccine’s availability, but, busy mom that I was, I had not yet made the trip to the health department to get the immunization for my two-year-old daughter, Sarah. I will always regret that bit of procrastination and the anguish that it caused.”
It is true that the risk may be very small for a disease like polio, which is close to being eradicated worldwide, but it is not zero.
Consider that the last case of polio occurred in 2005, when an unvaccinated 22-year-old U.S. college student became infected with polio vaccine virus while traveling to Costa Rica in a university-sponsored study-abroad program.
So you might not get wild polio unless you visit specific regions of Afghanistan or Pakistan, but you might want to be concerned about vaccine-associated polio if you go to a country that is still giving the oral polio vaccine.
And the risk is certainly much higher than zero for most other vaccine-preventable diseases, as we see from the regular outbreaks of measles, mumps, and pertussis, etc.
Some studies even suggest that delaying your child’s vaccines puts them at more risk for side effects once you do start to get caught up!
“…in the second year of life, delay of the first MMR vaccine until 16 months of age or older resulted in an IRR for seizures in the 7 to 10 days after vaccination that was 3 times greater than if administration of MMR vaccine occurred on time.”
Hambridge et al on Timely Versus Delayed Early Childhood Vaccination and Seizures
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.
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.
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.
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?
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.