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The study, which was posted this week on the BCCDC website, and has not yet been peer reviewed, also found that protection was only slightly reduced when it came to two variants of concern, the alpha variant (also known as the B.1.1.7 and associated with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
Widow looking for answers after Quebec man dies in Texas Ironman competition
The widow of a Quebec man who died competing in an Ironman competition is looking for answers.
Tom Mulcair: Park littered with trash after 'pilot project' is perfect symbol of Trudeau governance
Former NDP leader Tom Mulcair says that what's happening now in a trash-littered federal park in Quebec is a perfect metaphor for how the Trudeau government runs things.
World seeing near breakdown of international law amid wars in Gaza and Ukraine, Amnesty says
The world is seeing a near breakdown of international law amid flagrant rule-breaking in Gaza and Ukraine, multiplying armed conflicts, the rise of authoritarianism and huge rights violations in Sudan, Ethiopia and Myanmar, Amnesty International warned Wednesday as it published its annual report.
Photographer alleges he was forced to watch Megan Thee Stallion have sex and was unfairly fired
A photographer who worked for Megan Thee Stallion said in a lawsuit filed Tuesday that he was forced to watch her have sex, was unfairly fired soon after and was abused as her employee.
Amid concerns over 'collateral damage' Trudeau, Freeland defend capital gains tax change
Facing pushback from physicians and businesspeople over the coming increase to the capital gains inclusion rate, Prime Minister Justin Trudeau and his deputy Chrystia Freeland are standing by their plan to target Canada's highest earners.
U.S. Senate passes bill forcing TikTok's parent company to sell or face ban, sends to Biden for signature
The Senate passed legislation Tuesday that would force TikTok's China-based parent company to sell the social media platform under the threat of a ban, a contentious move by U.S. lawmakers that's expected to face legal challenges.
Wildfire southwest of Peace River spurs evacuation order
People living near a wildfire burning about 15 kilometres southwest of Peace River are being told to evacuate their homes.
U.S. Senate overwhelmingly passes aid for Ukraine, Israel and Taiwan with big bipartisan vote
The U.S. Senate has passed US$95 billion in war aid to Ukraine, Israel and Taiwan, sending the legislation to President Joe Biden after months of delays and contentious debate over how involved the United States should be in foreign wars.
'My stomach dropped': Winnipeg man speaks out after being criminally harassed following single online date
A Winnipeg man said a single date gone wrong led to years of criminal harassment, false arrests, stress and depression.