October 05, 2016
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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.