Canada investigating timing of second vaccine dose

Canada's chief public health officer says she has asked the national vaccine advisory panel to investigate if there is merit to delaying second doses of COVID-19 vaccines in a bid to get more people vaccinated faster with first doses.

The request comes after the United Kingdom said it will delay the second doses of vaccines from Pfizer-BioNTech and AstraZeneca, up to 12 weeks.

Pfizer-BioNTech's product is supposed to be given in two doses 21 days apart, and AstraZeneca's in two doses 28 days apart.

Health Canada has not yet authorized AstraZeneca's vaccine candidate but approved Pfizer-BioNTech's on Dec. 9 and another from Massachusetts-based biotech firm Moderna on Dec. 23.

A written statement from Pfizer says ultimately alternative dosing decisions are up to local health authorities, but that the company has no evidence protection after the first dose remains in place after 21 days.

Tam says the National Advisory Committee on Immunization is being asked to provide analysis on what is known about the dosing regimens and what should be considered in deciding whether or not to delay the second doses.