The National Advisory Committee on Immunization (NACI) is supporting B.C.’s decision to delay the second doses of COVID-19 vaccines by up to four months.
“NACI recommends that in the context of limited COVID-19 vaccine supply jurisdictions should maximize the number of individuals benefiting from the first dose of vaccine by extending the second dose of COVID-19 vaccine up to four months after the first,” the committee said in a decision published Wednesday (March 3).
The recommendation applies to all COVID-19 vaccines currently approved in Canada; Pfizer-BioNTech, Moderna and the newly approved AstroZeneca vaccine.
B.C. announced the decision to delay the second booster shot for four months on Monday, which health officials said could mean that all adults in the province could have their first dose by July.
Both provincial health officer Dr. Bonnie Henry and NACI said that its rationale was based on both the current available vaccine supply and data from other countries.
A study published by the University of Cambridge in the U.K., which has not yet been peer-reviewed, suggests that a single dose of the Pfizer-BioNTech vaccine can reduce the number of asymptomatic COVID-19 infections by 75 per cent.
In Israel, researchers studied the effects of a single dose of the same vaccine and published their findings in The Lancet medical journal, concluding that it was 85 per cent effective against symptomatic COVID-19 infections.
Also in The Lancet, a U.K. study found that the Oxford-AstraZeneca vaccine is 81 per cent effective when its second dose is given three months after the first, compared with 55 per cent efficacy after six weeks.
The national advisory committee noted that since the COVID-19 vaccines are still new, its unknown how long the protection of one or both doses lasts for.
“Experience with other multi-dose vaccines after a single dose suggests persistent protection could last for six months or longer in adolescents and adults,” NACI said in its statement. “Longer-term follow-up of clinical trial participants and those receiving vaccination in public programs will assist in determining the duration of protection following both one and two doses of vaccination.”
The national advisory committee added that it’s unknown how a delayed booster shot regime will affect the spread of variants of concern, including the U.K. and South African ones. However, NACI notes that there is “currently no evidence that an extended interval between doses will either increase or decrease the emergence of variants of concern.”
The committee noted that all three currently approved vaccines have shown “promising early result” against the U.K. variant B.1.1.7.
– with files from The Canadian Press
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