Health officials are warning Canadians to remain vigilant between their first and second doses of the COVID-19 vaccine as new evidence suggests that one shot of Pfizer may not offer strong protection against variants of concern.
The findings mirror what at least one doctor is seeing in a Canadian hospital where some individuals who’ve received their first dose are being admitted to ICU.
A new study published this week looked at health workers at two hospitals in the UK who received the Pfizer vaccine. It found those who had received one dose had a weaker immune response that could leave them vulnerable to infection by variants of concern.
“Our findings show that people who have had their first dose of vaccine, and who have not previously been infected with SARS-CoV-2, are not fully protected against the circulating variants of concern,” lead author Rosemary Boynton said in a news release. “This study highlights the importance of getting second doses of the vaccine rolled out to protect the population.”
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The health workers who had previously been infected with the “wild-type Wuhan strain” of COVID-19 had a stronger immune response after their first dose than their peers who had never been infected, suggesting natural immunity coupled with a first dose offers stronger protection.
The study analyzed the health workers’ blood for its immune response looking at the B.1.1.7. (UK) variant and the B.1.351 (South African) variants. Researchers believe the findings could also apply to the P.1. (Brazilian) and B.1.617 (Indian) strains.
The best defence, researchers added, is vaccination coupled with public health measures since a virus that can’t transmit won’t have a chance to mutate.
“As new variants continue to emerge, it is important to fast track global rollout of vaccines to reduce transmission of the virus and remove the opportunities for new variants to arise,” Boynton said.
The UK researcher’s findings support what’s happening in Canadian hospitals.
Toronto doctor Michael Warner tweeted earlier this week that he’s seeing COVID-19 patients admitted to ICU “well after” their first dose but before their second.
“One isn’t vaccinated until fully vaccinated,” he tweeted. “Given the significant delay between shots one and two, clear communication on how to conduct oneself between shots from public health leaders would help.”
Many Canadian provinces have widened the window between shots to four months to allow more people to get a first dose more quickly. Pfizer and Moderna both recommend both their doses be administered within a month of each other, but Canadian health officials say people will end up with the same high-level protection if that window is expanded.
In the meantime, health officials are reminding Canadians to follow public health measures such as masking and physical distancing after their first dose to avoid infection.
“We know there are some circumstances where people do contract COVID after receiving [the] first vaccine,” Ontario Health Minister Christine Elliott said. “However, clinical evidence shows us that people receive a high degree of coverage after [the] first vaccine and if they do need to be hospitalized, it ’s likely they’ll have a much milder case.”
She added Ontario is not looking to shorten the interval between first and second doses.
Canada’s Chief Public Health Officer, Dr. Theresa Tam, said Friday that variant of concern cases now account for a majority of infections in the country. The highly transmissible UK variant accounts for 95% of those variant cases.