This is a summary, written by members of the CITF Secretariat, of:
Grewal R, Kitchen SA, Nguyen L, Buchan SA, Wilson SE, Costa AP, Kwong JC. Effectiveness of a Fourth Dose of COVID-19 Vaccine among Long-Term Care Residents in Ontario, Canada: Test-Negative Design Study. medRxiv. 2022 June 1. DOI: 10.1101/2022.04.15.22273846.
The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.
A recent study demonstrates that a fourth dose of mRNA vaccine was highly effective at protecting residents of long-term care facilities against severe COVID-19 outcomes (86%), symptomatic infection (69%), and any SARS-CoV-2 infection (49%) during the Omicron-fuelled fifth wave. The research, released in pre-print and therefore not yet peer reviewed, was led in part by CITF-funded researchers Dr. Jeffrey Kwong from ICES and Dr. Andrew Costa from McMaster University.
Residents of long-term care homes in Ontario have been disproportionately burdened by COVID-19, accounting for nearly two-thirds of deaths during the first two waves of the pandemic. While vaccines have provided good protection, their protection wanes over time. This study found that roughly three months after the third dose vaccine effectiveness was 77% against severe outcomes, 55% against symptomatic infection, and 37% against any SARS-CoV-2 infection.
- Compared to unvaccinated individuals, vaccine effectiveness (VE) generally increased with each recent additional dose, a fourth dose being 86% effective against severe outcomes, 69% effective against symptomatic infection, and 49% effective against any type of infection. Each month after vaccination, there was a progressive loss of protection.
- Compared only to individuals who received a third dose, a fourth dose given at least 84 days after the third provided meaningful added protection against severe outcomes (40%), symptomatic infection (31%), and any type of infection (19%).
- Within the study timeframe (December 30, 2021 to April 27, 2022), 8% of LTC residents in Ontario were tested for SARS-CoV-2 by PCR. Most individuals who tested positive (58.1%) had been vaccinated three times at the time of testing positive
Starting December 30, 2021, Ontario offered a fourth dose to residents of long-term care aged 60 and older who had received their third dose at least 84 days prior. Nearly all (95%) of the provinces’ long-term care residents received Moderna’s Spikevax vaccine as a fourth dose.
(1) Vaccine effectiveness of a fourth dose was measured seven days or more after administration of the vaccine.