Low levels of detectable pertussis antibody among a large cohort of pregnant women in Canada (lay summary)

Brooks JI, Bell CA, Rotondo J, Gilbert NL, Tunis M, Ward BJ, Desai S. Vaccine. 2018 Oct 1;36(41):6138-6143. doi: 10.1016/j.vaccine.2018.08.066.

Pertussis or “whooping cough” is a highly contagious respiratory infection in children that can cause serious illness in infants. The rate of infection has dropped dramatically in Canada since vaccination programs were introduced. The pertussis vaccine is given to infants at 2, 4, 6 months and 18 months of age followed by a booster between 4 and 6 years of age as well as an adolescent booster at 14–16 years of age. A single additional dose is recommended for adults. Immunity (resistance) to pertussis can wear off with age. In Canada, about 65 infants in every 100,000 were infected with pertussis between 2011 and 2015. Pertussis vaccination during the last trimester of pregnancy has been shown to be successful in preventing pertussis in their infants.

The objective of this study was to estimate what percentage of pregnant women in Canada had antibodies to pertussis and therefore could protect their newborn infants from pertussis. Antibodies are substances produced by our bodies to destroy bacteria that cause infections. Second trimester blood samples from 1752 women from the MIREC Study were analysed for pertussis antibodies. The results showed that 97.5% of these women had pertussis antibody levels below 35 IU/mL, indicating no recent infection or vaccination for pertussis.

In conclusion, almost all of the pregnant women in this large cohort had pertussis antibody levels low enough to suggest that both the pregnant women and their newborn infants are susceptible to pertussis infections. Therefore there was likely little transfer of protection to pertussis from mothers to their newborns by the placenta.

The Canadian National Advisory Committee on Immunization now recommends routine immunization with a tetanus/diphtheria/pertussis vaccine in every pregnancy, regardless of previous immunization history.

This study was led by scientists at the Public Health Agency of Canada using maternal blood samples stored in the MIREC Biobank.