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Rapid decline in acellular pertussis vaccine protection warrants review
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The acellular pertussis vaccine offers waning protection over time and was associated with a more than twofold risk for infection compared with whole-cell vaccine, according to a review of public health records in Canada’s most populous province.
“This study highlights the need to re-evaluate strategies for pertussis vaccination in Canada and to spur vaccine development,” Natasha S. Crowcroft, MD, professor at the University of Toronto Dalla Lana School of Public Health and chief of applied immunization research at Public Health Ontario, and colleagues wrote in CMAJ. “We observed high early effectiveness of the pertussis vaccine that rapidly declined as time since last vaccination surpassed 4 years.”
In 1997, acellular pertussis vaccine replaced the whole-cell vaccine that had been in use in Canada since 1984. Crowcroft and colleagues used available public health records in Ontario to link patients born from April 1992 to January 2013 with pertussis PCR test results between Dec. 7, 2009, and March 31, 2013.
After excluding certain results — such as those from toddlers aged younger than 3 months and from people who may have received their primary vaccination somewhere else — the researchers were left with 5,867 patients. Among them, 486 tested positive for pertussis.
Adjusted vaccine effectiveness ranged from a high of 84% at 1 to 3 years (95% CI, 77-89) to a low of 41% at 8 or more years (95% CI, 0-66), Crowcroft and colleagues found. Efficacy was 80% between 15 and 364 days (95% CI, 71-86) and 62% from 4 to 7 years (95% CI, 42-75) for those vaccinated vs. unvaccinated patients.
Further, acellular vs. cellular vaccine priming was associated with an increase in the odds of pertussis (adjusted OR = 2.15, 95% CI, 1.3-3.57).
Crowcroft and colleagues concluded that pertussis vaccination strategies in Canada should be re-evaluated to potentially include whole-cell vaccine priming and/or boosters in pregnancy.
“Despite waning immunity of the whooping cough vaccine, it’s important to note that the number of cases of pertussis in Canada is still quite low,” Crowcroft said in a news release. “The most effective way parents can prevent whooping cough is to have their children immunized on time.”
Disclosure: The researchers report no relevant financial disclosures.
Perspective
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Edward A. Bell
The study by Schwartz and colleagues provides useful and important data, and adds “fuel to the fire,” that our current immunization policies and utilization of vaccine products need improvement. Data from this study demonstrated the waning immunity of pertussis vaccines, especially at 4 years and longer post-immunization. Study patients who received only acellular pertussis vaccines for the primary series were more likely to exhibit waning immunity than children who received only whole-cell vaccine products, with 2.2-fold greater odds of contracting pertussis when acellular vaccines were given.
Data from this Canadian study are similar to U.S. studies in demonstrating differences in efficacy between whole-cell and acellular vaccines (Klein and colleagues, 2013). Schwartz and others have concluded that we need improved pertussis vaccine products. Until these products are developed and available, we should improve utilization of the vaccines currently available. The CDC has reported that in 2014 only 21.5% of adults aged 19 to 65 years received Tdap, and only 32.5% of these adults living with an infant aged younger than 12 months received Tdap. Administering Tdap during every pregnancy, as has recently been recommended, occurs in only 14% to 23% of eligible women. These numbers should be improved upon and are likely to significantly decrease pertussis morbidity and mortality until new vaccines come along.
Disclosure: Bell reports no relevant financial disclosures.
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