The pertussis vaccine, which was introduced in combination with diphtheria and tetanus vaccines in the 1940s, consisted of whole pertussis bacteria inactivated with formaldehyde. Prior to the vaccine, every year about 8,000 children died from pertussis in the United States.
Because the original pertussis vaccine was made using the whole bacteria, it was called the whole-cell pertussis vaccine (wP). This vaccine contained about 3,000 structural and non-structural proteins from the bacteria as well as inactivated pertussis toxins (i.e., toxoids, including endotoxin). It was the only time we have ever routinely given a whole bacterial vaccine routinely to children in the United States. The wP vaccine dramatically reduced the incidence of pertussis disease and death. Unfortunately, the wP vaccine had a difficult safety profile, complicated by occasional high fevers, seizures with or without fever, high-pitched, inconsolable crying, and hypotonic-hyporesponsive syndrome. Although the vaccine never caused permanent harm (such as epilepsy or developmental delays), many in the media and the public believed that it did.
Because of these real and imagined issues of safety, in the late 1990s, the wP vaccine was phased out in favor of a vaccine containing only two to five inactivated pertussis proteins (i.e., the acellular pertussis vaccine [aP]). The result was a much better safety profile. But, as we’re learning over the past few years, the switch has also resulted in a dramatic decrease in vaccine efficacy.
During the past 15 years, outbreaks of pertussis in the United States have afforded researchers the opportunity to see what happened as we switched from the wP vaccine to the aP vaccine. Specifically, comparing children who had received:
- The whole cell pertussis vaccine only
- A priming dose or priming series with the wP vaccine followed by booster doses with the aP vaccine, and
- The aP vaccine only
Researchers found that while the wP vaccine was clearly better than the aP vaccine regarding efficacy. They also found that those who were primed with the wP vaccine and boosted with the aP vaccine were much less likely to get pertussis than those who received the aP vaccine only.
Using this information, Haedi DeAngelis and coworkers at New Mexico State University and Yale School of Public Health performed a mathematical modeling of pertussis in the United States should we now change our recommendation to include one dose of wP vaccine followed by only the aP vaccine (DeAngelis H, et al. Epidemiological and economic effects of priming with whole cell Bordetella pertussis vaccine. JAMA Pediatr. 2016 Mar 28. doi: 10.1001/jamapediatrics.2016.0047.) They estimated that this vaccine strategy would reduce the incidence of pertussis in the United States by 95 percent, including 96 percent fewer infections in neonates.
Although it is unlikely that such a strategy would ever be implemented, largely due to feared side effects of the whole cell pertussis vaccine, it is highly likely that the benefits of such a strategy would outweigh its risks.
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