This is a summary, written by members of the CITF Secretariat, of:

Jorgensen SCJ, Hernandez A, Fell DB, Austin PC, D’Souza R, Guttmann A, Brown KA, Buchan SA, Gubbay JB, Nasreen S, Schwartz KL, Tadrous M, Wilson K, Kwong JC, on behalf of the Canadian Immunization Research Network (CIRN) Provincial Collaborative Network (PCN) Investigators. Maternal mRNA covid-19 vaccination during pregnancy and delta or omicron infection or hospital admission in infants: test negative design study. BMJ. February 2023. DOI: 10.1136/bmj-2022-074035.

The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.

In a study published in BMJ, CITF-funded researchers Drs. Kumanan Wilson (University of Ottawa), Jeffrey Kwong (University of Toronto), and Deshayne Fell (Children’s Hospital of Eastern Ontario Research Institute) revealed that COVID-19 vaccination during pregnancy is effective at protecting the newborns from SARS-CoV-2 infections and hospitalizations, particularly during the first two months of life. Vaccination was more effective against Delta than Omicron infections. A third dose substantially increased vaccine effectiveness against the immune-evasive Omicron variant.

Key messages:

  • The vaccine effectiveness (VE) of two maternal doses against infection in their infants from the Delta variant was estimated to be 95%, and 97% against infant hospital admission due to a Delta infection.
  • VE of two maternal doses against Omicron infection in their infants and Omicron-related hospital admission were estimated to be 45% and 53%, respectively. VE against an Omicron infection was higher when the second vaccine was administrated during the third trimester (53%) compared with the first (47%) or second (37%).
  • VE of two maternal doses against Omicron infection in the infants decreased from 57% between birth and eight weeks to 40% after 16 weeks.
  • A third maternal dose increased VE against Omicron infection in the infant and hospitalizations to 73% and 80%, respectively.

This study included 8,809 infants younger than six months of age, born between May 2021 and March 2022, and who were tested for SARS-CoV-2 between May 2021 and September 2022. The mothers who were not vaccinated up to 14 days before their infant’s COVID-19 test were considered as unvaccinated.