Study confirms benefits of COVID-19 vaccines, shows effectiveness declines over time

A long-term study of the effectiveness of COVID-19 vaccines confirmed protection against SARS-CoV-2 infection, hospitalization, and death, but these benefits declined markedly over time.

The systematic review, published in Respiratory Medicine The Lancetanalyzed 68 studies that reported vaccine efficacy immediately and at least 112 days after a series of primary vaccines and at least 84 days after a booster dose.

“Our analyzes indicate that vaccine efficacy generally declines over time against SARS-CoV-2 infections, hospitalizations, and mortality,” the authors concluded. “Baseline vaccine efficacy levels for the omicron variant were significantly lower than for other variants. Therefore, other preventative measures (e.g., face mask wearing and physical distancing) may be needed to manage the long-term pandemic.

Investigators searched the Excerpta Medica database and the U.S. National Institutes of Health’s iSearch COVID-19 portfolio and manually searched COVID-19 sources for studies published between January 1, 2020 and the December 1, 2022. The research included the four COVID-19 vaccines licensed in Canada by Pizer-BioNTech, Moderna, Oxford-AstraZeneca and Janssen.

The study found that the overall efficacy of the primary series vaccine against infection was 83% between 14 and 42 days after vaccination and fell to 62% between 112 and 139 days and 47% after 280 days. . The initial efficacy against hospitalization was 92% and fell to 79% between 224 and 251 days. Against death, the efficacy was 91%, and fell to 86% between 168 and 195 days.

The effectiveness of booster doses was 70% against infection and 89% against hospitalization, and fell to 43% and 71% respectively at 112 days or more.

Vaccines were less effective against Omicron variants – 61% against infection and 71% against hospitalization between 14 and 42 days, falling to 21% and 52% respectively between 168 and 195 days.

The World Health Organization defines adequate efficacy as at least 70% against infection and at least 90% against hospitalization and death.

“We were surprised that the vaccines didn’t last very long and how much the Omicron variant really reduces efficacy,” said Simon Bacon, PhD, of the Department of Health, Kinesiology and Applied Physiology. from Concordia University in Montreal. Contagion.

The study was funded by the Canadian Institutes of Health Research and the Public Health Agency of Canada and could help health policymakers determine strategies to fight the virus.

“Vaccines work, although the effect diminishes within 3-4 months, this is true for both the primary series and boosters, so continuing to give booster doses is going to be important,” Bacon said.

The authors advocated mitigation measures such as wearing masks, physical distancing, and quarantining to reduce the spread of COVID-19 and said further research is needed to assess the effectiveness of protective measures. attenuation in vaccinated individuals.

All vaccine classes experienced similar declines in efficacy over time, but adenovirus vaccines had lower overall efficacy against infection than mRNA vaccines. Against hospitalization and death, the two classes of vaccines showed similar results.

From ages 14 to 42, efficacy against infection with any variant was 87% for mRNA vaccines and 69% for adenovirus vaccines, dropping to 66% and 56% respectively at 112-139 days. Effectiveness against hospitalizations increased from 93% to 89% during this period for mRNA vaccines and from 90% to 89% for adenovirus vaccines.

Bacon said research will continue to track the effectiveness of new booster doses and analyze various combinations of vaccines and hybrid immunity.

“If we have a different major variant, we would need to see how the vaccines resist that,” he said.