Graph tracks infections of long-term care home residents after they get their first doses of COVID-19 vaccine, Dec. 15, 2020 to Feb. 15, 2021. Infections fell off sharply after three weeks. (B.C. Centre for Disease Control)

Graph tracks infections of long-term care home residents after they get their first doses of COVID-19 vaccine, Dec. 15, 2020 to Feb. 15, 2021. Infections fell off sharply after three weeks. (B.C. Centre for Disease Control)

COVID-19 vaccine protects health staff, seniors best after three weeks

B.C. data show new infections dropped rapidly after first jab

There was a brief wave of worry in B.C. this week when provincial health officer Dr. Bonnie Henry reported that a COVID-19 outbreak at a Kelowna senior care home included new infections in people who have been vaccinated twice.

While seniors and their caregivers aren’t perfectly protected by vaccination, the effect has been dramatic since nurses, care aides and long-term care home residents reached three weeks after receiving their first doses. Data released by the B.C. Centre for Disease Control Thursday tracked new infections of all B.C. health care workers, and also residents of long-term care, assisted living and independent living facilities.

From Dec. 15, 2020 to Feb. 15, 2021, there were 203 coronavirus cases confirmed in long-term care homes, and 89 per cent of them occurred in the first 21 days after the vaccine was administered. After immune systems have three weeks to adjust to the vaccine, new infections all but disappear.

A similar trend is seen in data from health care workers over the same period. With employees subject to the risk of community exposure as well as at work, there were 346 new cases from Dec. 15 to Feb. 15 among B.C. health care workers. Again, 86 per cent of those infections occurred before each staffer reached 21 days with vaccine in their system, dropping to almost none afterward.

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Henry said those results were key to her decision to extend the maximum time between shots up to four months. After some initial objections, federal health experts have endorsed the move.

“This work has allowed us to understand the protection that we get, even in situations like long-term care homes with our most vulnerable of seniors and elders, that we can have excellent protection from a single dose,” Henry said in presenting the latest modelling data March 11. “And that is what has supported us to be able to make that really important decision to extend the interval for second doses so that we can protect more people more quickly, and win that race that we are in right now.


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