Immunity to the Acellular Whooping Cough Vaccine Wanes With Time Interview with:
Dr. Kevin Schwartz, MD MSc
Infection Prevention and Control Physician
Infection Prevention and Control
Public Health Ontario | Santé publique Ontario What is the background for this study?

Response: There has been a resurgence of pertussis, or ‘whooping cough’, in several countries and regions since the introduction of the new “acellular” pertussis vaccine in the 1990s to replace the older “whole cell” vaccine. In Ontario, we have not seen large increases but observed a small outbreak in 2012 that affected both unvaccinated people, as well as in those who have been vaccinated against pertussis. Our objective was to evaluate the effectiveness of the current acellular vaccine used in Ontario. We wanted to find out whether immunity wanes with time in the same way as had been previously observed during a large outbreak in California. We also wanted to study the impact of receiving the older ‘whole cell’ vaccine, which we used in Ontario until 1997. What are the main findings?

Response: The acellular pertussis vaccine was quite effective for about 3 years. We observed a significant decrease in the effectiveness (i.e. waning immunity) after 4 years, and minimal to no protection at all after 7 years from the last vaccine dose received. Another surprising finding: people who received the newer acellular version of the vaccine for their first three infant vaccine doses were twice as likely to contract pertussis compared with people who had received the older whole cell vaccine when they were infants. This finding was surprising since the older whole cell vaccine used in Canada was not particularly effective on its own, compared with other brands of whole cell vaccine used in the rest of the world. However, receiving 1 or more doses of the Canadian whole cell vaccine as a baby resulted in better protection years later in comparison to the newer, acellular version What should readers take away from your report?

Response: Pertussis is most severe for young infants. Most deaths from pertussis occur in babies under the age of 1-year. Our research showed our current vaccine still works well for protecting this age group.

Current research and practices suggest the best way to protect very young infants and babies is through vaccinating infants on time and vaccinating women while pregnant. The pertussis vaccine has been shown to be safe for pregnant women, and vaccinating pregnant women confers some immunity protection to infants and limits the likelihood that the child will contract the illness from their mother after birth. Also, ensuring that children and others in the household are immunized also helps protect infants and babies from contracting the disease.

The most important take home message for the public is to immunize their children on time to minimize the chances of infection.

Our research suggests we need to rethink our pertussis immunization program to consider whether we should include a whole cell vaccine for infant doses, or additional booster doses for adolescents and adults. What recommendations do you have for future research as a result of this study?

Response: We really need a better understanding of pertussis epidemiology. The optimal immunization strategy depends on who is getting the infection, which changes based on where you live. We hope there is additional research evaluating the approach of whole cell vaccine priming, which has the potential to significantly improve pertussis control. Most importantly, we also hope this study helps stimulate more research into new vaccine development. Ultimately, our hope is that a new and improved pertussis vaccine with longer-lasting protection can be developed based on what we have learnt about existing vaccines. Thank you for your contribution to the community.

Kevin L. Schwartz, Jeffrey C. Kwong, Shelley L. Deeks, Michael A. Campitelli,Frances B. Jamieson, Alex Marchand-Austin, Therese A. Stukel, Laura Rosella,Nick Daneman, Shelly Bolotin, Steven J. Drews, Heather Rilkoff,and Natasha S. Crowcroft

Effectiveness of pertussis vaccination and duration of immunity
CMAJ cmaj.160193; published ahead of print September 26, 2016,doi:10.1503/cmaj.160193

Note: Content is Not intended as medical advice. Please consult your health care provider regarding your specific medical condition and questions.

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