MONTREAL — A growing COVID-19 outbreak in the first Quebec long-term care to receive Pfizer’s vaccine is not a reason to question the shot’s efficacy, an infectious diseases expert said Wednesday.

As of Tuesday, there were 123 active cases of COVID-19 at the CHSLD Saint-Antoine in Quebec City, up from 98 cases two days earlier. The residence, which began vaccinating residents on Dec. 14, has reported 12 deaths from the disease during the pandemic’s second wave.

Local health authorities indicated on Tuesday that at least some of those who were infected had tested positive after receiving the vaccine.

Benoit Masse, a public health expert at the Universite de Montreal, said the rising case numbers in the home are not surprising, given that the outbreak began before inoculations got underway.

“The vaccine prevents, but if (the virus) is already present, it won’t help much,” said Masse. “It’s the equivalent of putting sunscreen on a sunburn.”

Masse says that, like with other vaccines, it takes about two weeks following the injection for the body to build an immune response, meaning the vaccine is of little use in preventing illness before then.

“That’s why we do flu vaccination campaigns in October, when we expect the virus will arrive in Montreal in November or December,” he said.

While he’s not surprised to see the outbreak continue to grow, Masse worries it could lead to the erroneous belief that the vaccine doesn’t work, or even that it’s harmful.

Roxane Borges Da Silva, another Universite de Montreal public health expert, says it’s worth asking whether staff at the care home became complacent once the vaccination program began.

“Knowing that it’s one of the first long-term care homes to be vaccinated, was there a carelessness in the application of (infection control) measures?” she wrote in an email.

In a statement, the Quebec City health authority said the outbreak at the CHSLD Saint-Antoine began after it was chosen as a vaccination site but before shots began.

“The too short time for antibodies to develop fully in vaccinated people did not allow some residents or workers to avoid developing symptoms, as they had most likely already been exposed to COVID-19, given the context of an outbreak,” spokesman Mathieu Boivin said in a statement.

He said it’s possible the vaccinated residents and workers will experience less severe symptoms of COVID-19, but it’s too soon to say for sure.

He also stressed that those who were infected have not yet received their second doses of the vaccine, even though the efficacy of a first dose is believed to be over 90 per cent after 14 days, he said.

Boivin said the residents who tested positive after vaccination would receive their second doses at the same time as the rest, and that the outbreak wouldn’t affect vaccination.

Masse said more outbreaks are to be expected in care homes after vaccination campaigns begin.

“We’re in a race to vaccinate before the virus arrives in those environment,” he said. “If we get there too late, or we get there during an outbreak, the vaccine won’t succeed in preventing a large outbreak in those places.”

While the vaccination campaign has yet to make a dent in the number of new infections, hospitalizations and deaths in the province, he sees reason for optimism.

Masse believes the province could begin to see some improvement by the end of January, when the province finishes vaccinating those in long-term care homes. Things should look even better by March, when most of those over 80 could be immunized.

In the meantime, he’s urging Quebecers to respect the lockdown measures being put in place in the coming days, which he views as “one last, big effort” to get through the crisis.

This report by The Canadian Press was first published Jan 7, 2021.

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