QUEBEC CITY -- The COVID-19 vaccine is said to be about 80 per cent effective after a first dose in the elderly and health-care workers in Quebec.

That level of protection was qualified as “high” by the Quebec Institute of Public Health (INSPQ), which released preliminary data on the vaccine’s rollout so far.

However, there was a difference between the two groups: among health-care workers, immunity kicked in after two weeks, while it took three weeks to set in for those over 80.

The data remains preliminary, considering the timeframe is short, and only a handful of CHSLD residents received the vaccine in mid-December before the pace picked up in January.


With delivery delays slowing the province’s rollout in the early stages of vaccination, the province decided to postpone the administration of the second dose up to 90 days after the first. 

Quebec said it did this to offer a first dose to as many people as possible while it waited for more doses to arrive.

But debate arose around that decision, which went against recommendations from Pfizer and Moderna. The companies said people should receive a second dose within 21 or 28 days, depending on the vaccine.

On Thursday, during the technical briefing, the INSPQ said its findings don't contradict the province's decision. On the contrary, immunity is considered to be very good after a first dose, according to the institute.

“There is no great urgency to give the second dose, because the first is working well,” said Gaston De Serres, an epidemiologist at the INSPQ.

While early trials showed a shorter delay between the first and second doses of the Pfizer vaccine resulted in 95 per cent efficacy, one expert told CTV News it's better to favour a longer delay if it means more people can get a shot. 

"When you look at it, you want to be able to answer [for] yourself the following question: do you want to give 50 people 95 per cent protection? Or do you want to give 100 people 80 to 90 per cent protection?" said Donald Vinh, an immunity and infections expert at the MUHC.

"I think that for the betterment of society, the latter answer is probably the best."

One thing that still isn't known is when that immunity starts to subside.

The INSPQ says it will continue to monitor immunity levels, saying the organization is prepared to recommend a different schedule if data shows immunity is not sufficient under the current plan. 

As for newly emerged COVID-19 variants, preliminary data indicates vaccines administered in Quebec, those from Pfizer and Moderna, provide protection against them.

This report from the Canadian Press was first published, with files from CTV News Reporter Rob Lurie, on Feb. 18, 2021.