Single dose of Pfizer or Moderna enough to prevent COVID-19 infection in two-thirds of cases, new B.C. study finds
A new study from the B.C. Centre for Disease Control found that a single shot of Pfizer or Moderna COVID-19 vaccines reduced the risk of infection in British Columbians 70 and older by about two-thirds.
The study, which was posted this week on the BCCDC website, and has not yet been peer reviewed, also found that protection was only slightly reduced when it came to two variants of concern, the alpha variant (also known as the B.1.1.7 and associated with the U.K.) and the gamma variant (or P.1, associated with Brazil).
“This is wonderful news and especially meaningful because this was protection that was provided during the peak of pandemic risk,” said Dr. Danuta Skowronski, the study’s lead author.
Skowronski, the BCCDC’s epidemiology lead of influenza and emerging respiratory pathogens, added that she was “thrilled” and “energized” by the findings, which she said likely underestimated the protection warded by a first dose.
The BCCDC collected 16,993 specimens from adults 70 and older living in the community in British Columbia, rather than in long-term care.
Researchers collected the samples during the peak of the spring 2021 wave, between April 1 and May 14.
“Such protection is particularly meaningful considering that it was provided during a period of peak pandemic risk, when (variants of concern) were predominantly contributing to the epidemic in BC,” wrote the study’s author, Dr. Danuta Skowronski.
Researchers found vaccine effectiveness was negligible for the first two weeks after a shot.
Effectiveness increased to 43 per cent during week three, and to 75 per cent during week five, the study said.
Overall vaccine effectiveness three weeks after the first dose was 72 per cent for non-variants of concern, 67 per cent for the alpha variant, and 61 per cent for the gamma variant.
Skowronski pointed out that this appears to be the first study globally that broke out vaccine effectiveness on the gamma variant and said she was “heartened” by all the results.
Researchers did not examine the question of how long protection from a single dose of mRNA vaccine against COVID-19 infection might last.
That work is ongoing, Skowronski added, as large numbers of British Columbians begin to receive their second doses.
“Will there be a new variant? Will the vaccines be very effective over time? And those are the things that keep me up at night,” said the BCCDC’s medical director, Mel Krajden.
Skowronski added the research will also help determine whether British Columbians will need a third, booster dose at some point.
But she pointed out the fact the province extended the gap between the first and second doses, originally up to four months, could have an intended positive benefit of “higher boost responses.”
“It’s not a done deal that we’re going to need a third, booster dose,” she said.
CTVNews.ca Top Stories
BREAKING 4th Indian national arrested, charged with murder of Hardeep Singh Nijjar
Homicide investigators in B.C. say murder charges have been laid against a fourth Indian national in connection to the killing of Sikh activist Hardeep Singh Nijjar outside a Surrey gurdwara last year.
Man arrested after allegedly caught trespassing at Drake's Bridle Path mansion
Toronto police say a man has been taken into custody after he was allegedly caught trespassing at Drake's mansion in Bridle Path Saturday afternoon.
Wildfire that forced evacuation of Fort Nelson, B.C., caused by tree falling on wires, mayor says
The wildfire that prompted the evacuation of more than 3,000 people near Fort Nelson, B.C., was caused by a tree falling on wires, according to the municipality's mayor.
Eurovision Song Contest final kicks off after protests, backstage chaos and a contestant's expulsion
The 68th Eurovision Song Contest finally got down to musical business Saturday in the Swedish city of Malmo after days of protests and offstage drama that have tipped the feelgood musical celebration into a chaotic pressure cooker overshadowed by the war in Gaza.
Couple randomly attacked, 1 stabbed, by group of teens in Toronto, police say
A man has been transported to hospital after police say he was stabbed in a random attack carried out by a group of teens in Toronto on Friday night.
'I am angry': Alberta farmers will continue fight over world class motorsport resort
The rolling hills leading to the hamlet of Rosebud are dotted with sprawling farms and cattle pastures -- and a sign sporting a simple message: No Race Track.
IN PICTURES Northern lights dance across the night sky in southern Ont.
From London, to Grand Bend, Collingwood and Guelph, here are some highlights of Friday night and Saturday morning's northern lights display.
Ron Ellis, who played over 1,000 games with Maple Leafs, dead at 79
Ron Ellis, who played over 1,000 games with the Toronto Maple Leafs and was a member of Canada's team at the 1972 Summit Series, has died at age 79.
opinion How to use your credit card as a powerful wealth-building tool
Irresponsibly using a credit card can land you in financial trouble, but personal finance columnist Christopher Liew says when used properly, it can be a powerful wealth-building tool that can help grow your credit profile and create new opportunities.