Re: Despite high rates of vaccination, pertussis cases are on the rise. Is a new vaccination strategy needed?
WHOLE CELL PERTUSSIS VACCINE AND ADVERSE EFFECTS
Mara Kardas-Nelson (BMJ 7 July 2019) mentions that recent pertussis outbreaks have prompted some in the public health community to suggest that we bring back the whole cell pertussis vaccine/wP. She may be referring to May 2016 articles in JAMA Pediatrics by Sawyer, DeAngelis and colleagues. She also points out that in the 1970s parents in the US and UK began blaming wP vaccine for epilepsy and other problems. One of the “other problems” was SIDS, which was an important concern for pediatricians at the time.
A good place to look at the wP/SIDS problem is an article by Fine and Chen, “Confounding in Studies of Adverse Reactions to Vaccines”, Am J Epidem 1992:136;121. They reviewed studies of DTwP and the risks of SIDS and childhood encephalopathy. They show in their Table 1 that the risk factors for these adverse events are the same as the risk factors associated with avoidance or delay of vaccination, a number of social, perinatal and infant medical factors. They assert that, as a consequence, studies that fail to control for these confounders will underestimate any real risks associated with vaccination. They report that the odds ratios found in studies of DTwP and SIDS ranged from 0.15 to 7.50. They developed mathematical expressions and used them to show the substantial degree to which failure to adjust for confounders reduced the real risks of SIDS associated with DTwP, and which they summarized in Table 6. Fine and Chen never provide a summary estimate of SIDS risk associated with DTwP. However , they cast serious doubt on studies that have been cited to dismiss a causal role for DTwP, particularly the study by Griffin, et al, NEJM 1988;319:618.
The “Back to Sleep” campaign has been widely credited for the US decline in SIDS rates during the 1990s, but the evidence is circumstantial. The evidence that SIDS began to decline following the decline in our use of wP vaccine is at least as persuasive. This is reinforced by the sharp decline in SIDS in Japan during the 1970s and 1980s, when administration of wP was deferred until after 2 years of age. (Noble, et al. JAMA 1987;257:1351. Nakayama, J infect Chemother 2013;19:787)
SIDS wasn’t the only concern with wP. It regularly caused high fever, irritability, anorexia, and large painful swelling at injection sites. Less frequently it caused convulsions, prolonged screaming fits, and weird hypotonic-hyporesponsive episodes. Some epidemiologic studies showed associations with encephalopathy/brain damage. Those of us who practiced pediatrics in the 1970s and 1980s cringe when someone suggests a return to wP.
Fine and Chen conclude their article with this statement: “Most published discussions of adverse reactions to vaccinations have concentrated on biases that act to overestimate the relative risk of adverse events after vaccination. Biases that underestimate risk, as discussed here, have received much less attention….The avoidance of so many potential confounding factors presents a difficult challenge to epidemiologists who would study the problem of rare, severe adverse reactions to vaccines.”
We do need a pertussis vaccine that is safer than wP but more effective than the current acellular vaccine.
ALLAN S. CUNNINGHAM 16 July 2019
Competing interests: No competing interests