Pfizer-BioNTech, Moderna COVID-19 vaccines need two doses, Health Canada says, amid conflicting messaging from Quebec

Elisabetta Bianchini
·4-min read

Dr. Supriya Sharma, Health Canada’s chief medical advisor, cautioned against health experts advising that the single shot of either the Pfizer-BioNTech or Moderna vaccines can offer a high level of immunity.

This comes after Dr. Gaston De Serres, an infectious disease expert at the Institut National de Santé Publique du Québec, told CBC’s As It Happens that 14 days after the first dose of the the Pfizer-BioNTech vaccine, it provides “92 per cent protection.”

“Both Pfizer and Moderna are two dose vaccines,” Dr. Sharma said at a press conference on Friday. “You do need the second dose to get to that peak effectiveness.”

She identified that for the Pfizer-BioNTech vaccine in particular, it has about 52 per cent efficacy before the second dose, but confirmed that there is data that has stated that efficacy is at 89 per cent of 92 per cent in between the two doses.

“The difference, in terms of those numbers, is because some people, when they do the calculation, take out the first two weeks after you get the first dose,” Dr. Sharma explained.

This is done because there is not an instantaneous effect once someone receives the first shot, so some people looking at this data will remove the first 10, 12 or 14 days when determining effectiveness.

“This is a bit of the back of the envelope calculation on that,” Dr. Sharma said. “The studies were not designed to look for that sort of information.”

You should be getting the second dose, doctor urges

“I think a lot of people are interrupting the efficacy, the effectiveness of the vaccine as sort of, if someone gets the vaccine you can take a blood test and you say you’re at 95 per cent, or you’re at 89 per cent or you’re at 52 per cent, that’s not really the case.”

She added that the effectiveness of the vaccines is determined in studies based on how many cases there are in the group that did not get the vaccine versus the group that did. Dr. Sharma also said there are still questions about how long that immunity will last.

“Both assessments are appropriate, there’s different ways of look at that data, but the bottom line is these are two-dose vaccines, you should get the second dose,” she said.

“The second dose should be as close to the approved schedule as we can and the way that we know about the 95 per cent or the 94 per cent effectiveness is really based on getting that second dose, and we’re still continuing to see how long that effectiveness lasts.”

Maj.-Gen. Dany Fortin, vice-president of logistics and operations at the Public Health Agency of Canada and head of vaccine distribution efforts, confirmed that Canada is expected to receive six million doses of COVID-19 vaccines by the end of March.

Moderna shipments are set to arrive in Canada every three weeks. By the end of next week, 171,600 doses will be delivered. In the first week of February, about 170,000 will arrive in Canada. Maj.-Gen. Fortin expects doses to “scale up” to 250,000 in the month of February and by the end of March, two million doses of the Moderna vaccine should be distributed.

Pfizer-BioNTech vaccine doses are delivered to Canada on a weekly basis. This week 124,800 doses were delivered and for the remainder of January about 208,650 doses will arrive weekly. In February, Maj.-Gen. Fortin expects to receive between 366,000 and 367,000 dose of the Pfizer-BioNTech vaccine per week. By the end of March, Canada should receive four million of this vaccine in total.

‘We are all pushing the same direction’

Federal officials also spoke about a number of provinces, including Ontario and Quebec, stating publicly that they are “running out” of COVID-19 vaccine doses.

“We are all pushing the same direction,” Anita Anand, Minister of Public Services and Procurement said. “We have been clear with our delivery schedules, we have been clear that we will be ramping up with the doses that we are delivering to the provinces.”

“This is information that the provinces have and that they can use for their planning purposes. The phrase ‘running out of vaccines’ has to be taken in that context.”

Dr. Theresa Tam, Canada’s chief public health officer, also announced that as COVID-19 vaccines are distributed to Canadians, the federal government is working with provinces and territories to publicly share information on any adverse events following immunizations, to be updated on a weekly basis.

Dr. Tam stressed that these include any adverse events that happen after immunizations, “but not necessarily caused by the vaccine.” She added that these could range from common events like soreness at the injection site or severe events like serious allergic reactions.

To date, there have been nine adverse events reported in Canada, with no unanticipated vaccine safety issues identified.

“Canada has a robust vaccine safety monitoring system in place and all serious event will be investigated,” Dr. Tam said.

Check out our COVID-19 in Canada topic page for latest news, tips, health updates, cases and more.