Pertussis Vaccine: The Good, the Bad and the Ugly
Feb 11, 2016

Last week, a new study published in Pediatrics suggested that the pertussis immunity from the recommended adolescent Tdap booster was quick to wane.  While this is being reported by many as “news”, public health experts, immunologists and epidemiologists have long been familiar with the torrid history of pertussis vaccines and the unfortunate reality that the current pertussis vaccine does not provide long term protection.

Ever since the acellular pertussis vaccine was introduced in the late 90’s (DTaP), several studies have suggested that the pertussis immunity didn’t last as long as the previous whole cell pertussis vaccine (DTP) that first became routinely recommended for children back in the 1940’s and 1950’s.

In fact, waning immunity among the adolescent population is precisely what prompted the Advisory Committee on Immunization Practices (ACIP) to recommend an adolescent Tdap booster at ages 11-12 back in 2006.  At the time, the immunity received from recommended series of DTaP shots administered at ages 2, 4, and 6 months, with boosters administered at ages 15-18 months and again at 4-6 years of age, was determined to be waning in teens, so an adolescent booster was added to the recommended schedule as well as a recommendation for adults to receive one Tdap booster as well.

So why is last week’s study creating such a fuss when the data is not much different than what has been seen in previous studies?  

Last week’s study determined that effectiveness during the first year after adolescent Tdap vaccination was 69% but then decreased to 9% by four or more years after vaccination.  The study concluded that Tdap vaccine provided moderate protection against pertussis during the first year and then waned rapidly so that little protection remained 2-3 years after vaccination. It also concluded, like many studies before, that adolescents who were more remote from Tdap were significantly more likely to test positive for pertussis than were those vaccinated more recently.

But even as far as 2005, we see similar trends in the published data.  One such review on duration of immunity revealed that infection-acquired immunity against pertussis disease wanes after 4-20 years and protective immunity after vaccination wanes after 4-12 years. In 2014, another study looked into the evidence of rapidly waning immunity and the difference in effectiveness by Tdap brand. The results showed that immunity waned to 75% after one year, 68% after two years, 35% after three years and 12% after the fourth year with a slightly higher estimate among one brand than the other.  Then in 2015, another study investigated Tdap effectiveness among adolescents who received only acellular pertussis vaccines and found 73% effectiveness one year after vaccination, 55% effectiveness one to two years after vaccination, and 34% two to four years after vaccination.

The latest data really doesn’t offer a lot of new information, except that the numbers are slightly worse than we’ve seen in the past.

In response to these repeated findings,  many are questioning whether the ACIP will  consider changes to the adolescent and adult Tdap booster recommendations? 

The short answer is probably not.  But to understand why, we must look at how we’ve come to be where we are today.

Pertussis vaccines first became available back in the 1920’s, but it wasn’t until the 1940’s and 1950’s that a pediatric whole cell pertussis vaccine (DTP) became routinely recommended for children.  It was considered a good thing at the time because in the mid-1930’s to 40’s, the United States was suffering with more than 200,000 pertussis cases and over 4,000 pertussis-related deaths each year. Fortunately, after the routine use of childhood whole cell pertussis vaccine, the number of reported pertussis cases declined dramatically. By 1970, the reported incidence had declined greater than 99% and we hit a historic low of just 1,010 cases in 1976.

But before long, the pertussis predicament got ugly again.

As Dr. Paul Offit elaborates in his book Deadly Choices, and Seth Mnookin covers in detail in his book The Panic Virus, everything changed in the spring of 1982, when the local NBC affiliate in Washington, DC, aired a program entitled “Vaccine Roulette”.  It was then that reporter Lea Thompson kicked off a campaign of fear in her hour-long special. Pertussis cases were low at the time, and people no longer feared infection from a bacteria that made it near impossible to breath.  Instead, Thompson introduced new fears by featuring the personal narratives of parents who alleged that their children had suffered permanent injury as a result of the pertussis vaccine.  Thompson’s reporting not only struck to the core of a parent’s overwhelming instinct to protect their children, but it aggressively attacked the “medical establishment” for mandating the vaccine for public school children and willfully ignoring the horrible consequences of injury.

In the days after the special aired, one viewer, Barbara Loe Fisher, was so captivated by the concerns Thompson raised about the pertussis vaccine, that she was moved to take action. Two years prior, Fisher’s son had received his fourth DPT shot.  Fisher alleged that within hours of vaccination he suffered a convulsion to which she attributed brain inflammation that left her son suffering with multiple learning disabilities and attention deficit disorder.   Thompson’s “Vaccine Roulette” inspired Fisher to seek out other parents who suspected vaccine injury.  She subsequently co-founded the National Vaccine Information Center, and just like that the modern day “anti-vaccine” movement was born.

From there a whole lot of bad has happened, mixed in with some good.

While Fisher was poised to distinguish herself as a consumer advocate, who could have helped to institute vaccine safety reforms at a time when the public health system was evolving, she has since become a harsh critic of vaccines, advocating for alternative medicines over vaccines and promoting her belief that all vaccines are dangerous and ineffective.

Raising concerns about the safety of whole-cell pertussis vaccines prompted the development of a more purified (acellular) pertussis vaccine (DTaP) that was first licensed in the early 90’s.  By the year 1997, the ACIP recommended DTaP be used routinely in place of DTP for the full 5-dose pediatric schedule.  The good news was that it appeared less likely to provoke adverse events because these newer vaccines contain purified antigenic components of Bordetella pertussis.  The bad news is that the newer acellular pertussis vaccine is just not as effective in providing lasting immunity as the whole cell version.  This is exactly what we have been reminded of with last week’s study.

There is no doubt that we will continue to see cyclical peaks in pertussis, and it’s believed that these are not solely due to increased numbers of families exempting their children from vaccines.  The increase in pertussis can also be attributed to several other things such as decreased vaccine efficacy, waning immunity among adolescents and adults vaccinated during childhood, increased diagnosis and reporting of pertussis because of greater awareness among physicians about the disease, and enhanced surveillance and more complete reporting of the disease.

In an attempt to compensate for the vaccine’s waning immunity, the ACIP continues to assess the current data and alter recommendations as needed.

Even though there are several recommendations pertaining to pertussis vaccine, Every Child By Two (ECBT) continues to field questions from parents asking why the ACIP doesn’t simply recommend more frequent Tdap boosters.  Couldn’t we prevent more pertussis cases if everyone was recommended a booster once every 4-5 years?

Certainly that solution sounds logical.  However, ACIP recommendations come at a cost.  Based on the evidence of limited immunity offered from the vaccine, it appears that it is unlikely that the ACIP will recommend more frequent boosters.

In fact, in 2013 a special working group for the ACIP analyzed information to determine if it would be beneficial to add an extra dose of whooping cough vaccine to be admin
istered at either age 16 or 21. They concluded that an extra dose would only slightly reduce the number of whooping cough cases, but would come at a high cost. They estimated that adding a dose at age 16 would cost the U.S. $77 million more than the current vaccination program, or about $270,000 for each case of whooping cough that was prevented.  Whereas, an extra dose at age 21 was estimated to cost $23.5 million more and $139,000 per case prevented.  Since young adults infected with whooping cough don’t often become sick enough to require hospitalization, it was determined that the cost-benefit was not justified at that time.

However, as morbidity and mortality reports began noting that infants had a substantially higher rates of pertussis and the largest burden of pertussis-related hospitalizations and deaths, the ACIP began addressing these concerns with new vaccine recommendations. Research determined that in 85% of infant cases of pertussis, when the source of infection could be identified, the infection was found to be passed on from a mother or other member of the immediate or extended family.

This information has since led to numerous ACIP pertussis vaccine recommendations. 

First, in 2008, the ACIP recommended pregnant women receive a Tdap booster in the postpartum period in hopes that they would be less likely to pass on infection.  The recommendation was later updated in 2011 to include pregnant women and anyone who anticipates having close contact with infants under 12 months of age.  Not only does this help prevent infection of the mother who may later pass pertussis on to her child, but it also helps provide protective maternal antibodies to the unborn baby.  They are then given some level of protection before they can begin getting their own pertussis vaccination at two months of age.

Then, in 2013, the ACIP began recommending that pregnant women receive a Tdap booster in the third trimester of each pregnancy.  This is important given the fact that the amount of antibodies in your body is highest about 2 weeks after getting the vaccine, but then starts to decrease over time.  Vaccination during every pregnancy ensures that each baby gets the greatest amount of protective antibodies possible.

Additionally, since 2006, it’s been recommended that every adult get a Tdap booster once in their lifetime, and yet it’s estimated that only 26% of adults have even had this recommended Tdap booster.

While the current ACIP recommendations are expected to help reduce the incidence of pertussis in infants, organizations such as Every Child By Two (ECBT) are helping to educate the public about the importance of Tdap vaccinations for pregnant women, adolescents and adults.  ECBT’s new Vaccinate Your Family program promotes the benefit of vaccines for all age groups.  A suite of new shareable materials, such as their Grandparent Toolkit, have been specifically designed to highlight the importance of protecting newborns by vaccinating those around them.

 

So, while the future of pertussis vaccine recommendations remains in question, we will continue to monitor the discussion at upcoming ACIP meetings and use this forum to communicate any changes that are being discussed.  By subscribing to this blog, you’ll receive notification of our coverage of all the future ACIP meetings, to include one scheduled at the end of February, 2016.

For many, the biggest question of all is when will we see a new and more effective vaccine? While there certainly is a need, there doesn’t appear to be any promising alternatives on the horizon. 

For now, the best we can do is adhere to the recommendations in place and encourage others to do the same.  

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