2. STRETCH OUT SHOTS

Both Pfizer and Moderna are two-dose vaccines, with a 21-day (Pfizer) and 28-day (Moderna) wait between the first jab and the booster. The Pfizer trials suggest protection starts kicking in 10 to 12 days after the first dose. CTV reported this week that seven residents of a nursing home in western Montreal have tested positive for COVID after getting their first shot. The infections occurred within 28 days of vaccination, meaning they could have started before vaccine protection kicked in. Still, the reports are fraying nerves over Quebec's decision to space doses out up to 90 days in order to vaccinate more people.

“There's been a little bit of polarization of view on vaccine timing in Canada,” said Naylor, with “fundamentalists” wanting to hold back equal numbers of second doses, to ensure strict compliance with the authorized dosing schedule, and “absolute speed demons who want first doses yesterday and second doses whenever.”

Most of Naylor's colleagues are taking a pragmatic approach, he said, aligning with Canada's National Advisory Committee on Immunization (NACI), as well as a World Health Organization scientific group, both of which have decreed doses can be stretched to 42 days apart in exceptional circumstances — severe shortages, for example.

The concern? While the first dose is considered protective, though not fully, it's not known how long that protection lasts, a worry given the variants and the potential for creating “made-in Canada mutants,” Naylor said. The second shot also provides a dramatic boost in immune response.

On the other hand, given the grim supply shortages some provinces find themselves in, a slight delay — going out to six weeks — may be necessary, on and off, to manage supply chain wobbles and avoid holding back large numbers of shots that could cost many vulnerable lives, Naylor said. In the Pfizer trial, some people received their second dose as early as 19 days, and as many as 42 days after the first.