How important is timing with the second dose of COVID-19 vaccine? Here's a UBC researcher's answer

VANCOUVER -- With COVID-19 vaccine distribution expected to ramp up in the coming weeks, a B.C. researcher is shedding light on what individuals can expect when getting their second dose.

On Monday, the Public Health Agency of Canada announced it's expecting an increase in Pfizer-BioNTech after a month-long slowdown. More than 400,000 doses are expected to be sent to the country this week and eventually, 450,000 doses are expected to be delivered weekly until the beginning of April. 

When those delays in vaccine shipments were announced, B.C.'s top doctor extended the time between doses from 35 to 42 days. 

Dr. Manish Sadarangani, associate professor at the University of British Columbia's faculty of medicine, said in an interview posted to the school's website that a delayed second dose is unlikely to be detrimental, even if it's received outside the recommended timeframe. 

"Because of the pandemic’s widespread effects, we want to fully vaccinate Canadians as quickly as possible, while of course maximizing the effect of the first shot," Sadarangani said.

Even while waiting for the second dose, Sadarangani said there isn't a high chance someone who has received their first shot will get COVID-19.

"It’s unlikely you would contract COVID-19 after the first shot due to the first shot’s efficacy, although it’s important to remember that it takes approximately two weeks for protection to start after getting the first dose," he said.

"If you are exposed to the virus in the first few weeks after receiving the first shot, there’s a possibility you could contract COVID-19."

And if someone did get COVID between their shots, they'd still get the second dose once they've recovered.

Sadarangani warned that even those who've been vaccinated will need to remain cautious for now. For some, the vaccine may not work as well, especially for those who have health conditions that normally supress their immune system. Sadarangani said the best thing to do is consult a family doctor or specialist.

Sadarangani also said while it's still unclear whether the Pfizer-BioNTech and Moderna vaccines prevent transmission of COVID-19, rather than just protecting a person against it, inoculating more of the population could help reveal that.

"Transmission prevention was not part of the clinical trials," he explained. "But once we vaccinate enough people, we’ll start to see a decline in transmission if the vaccines prevent transmission."