Summary (Effectiveness against infection)
1st dose 52%
After 14-21 days 92%
After 7 days 95%
After 14 days 92%
After 14 days 94%
After 22-90 days 76%
2nd dose (given 12 weeks later) 82%
(4) Johnson & Johnson
After 14 days 66%
(5) Sputnik V
After 21-90 days
After 84-112 days
After 28-42 days
50%-65.9% but antibodies fade after 6 months, so a 3rd (booster) shot might be needed.
How long does it take for the COVID-19 vaccines to become effective?
Published April 26, 2021 3:53 p.m. ET
Updated April 27, 2021 2:52 p.m. ET
By Stephanie Liu
Pfizer-BioNTech, Canada’s first authorized vaccine, is effective in preventing both COVID-19 symptoms and severe outcomes caused by COVID-19, such as severe systemic illness, respiratory failure, shock, acute renal, hepatic or neurologic dysfunction, admission to an intensive care unit, or death, according to the Government of Canada.
The data shows that after the first dose and before the second dose, the estimated efficacy of the Pfizer-BioNTech vaccine is initially 52 per cent effective, but then becomes 92 per cent effective 14-21 days after the first dose.
One week after the second dose is administered, the Pfizer-BioNTech vaccine will be 95 per cent effective in preventing symptomatic COVID-19 and severe outcomes related to it.
Moderna was authorized by Health Canada in late December 2020 and offers protection against symptoms and severe outcomes of COVID-19. The vaccine has an 80 per cent efficacy rate after the first dose and increases to a 92 per cent efficacy rate 14 days later. Two weeks after the second dose is administered, the vaccine will be 94 per cent effective.
AstraZeneca will be 76 per cent effective in protecting individuals from COVID-19 and its related symptoms 22-90 days after the first dose.
When the second dose is administered 12 weeks or more later, the vaccine then becomes 82 per cent effective in preventing COVID-19, with immunity building over time.
Johnson & Johnson is Canada’s first single-dose vaccine that has been authorized. The vaccine is 66 per cent effective in preventing COVDI-19 two weeks after the vaccine is administered, and immunity will develop over time.
Correction: This article previously cited a 63 per cent efficacy rate for the second dose of AstraZeneca when taken two weeks after the first dose, which may have been interpreted as a drop in efficacy from
the first dose. However, confidence intervals in the range of data from studies vary. As additional analyses have found around an 82% efficacy rate after a second dose, when given 12 weeks or more following the first, we are no longer citing the 63 per cent number under AstraZeneca.