Health
What you need to know about getting both doses of the COVID-19 vaccine – CBC.ca
Getting vaccinated to protect yourself from the virus behind COVID-19 isn’t a one-and-done process in Canada right now.
The two approved options, from Pfizer-BioNTech and Moderna, both require a two-dose regimen, with each dose ideally spaced apart by a specific time interval that was used during clinical trials.
But that’s not how every region is handling the vaccine roll-out. While Ontario is striving to hold back enough doses so people get both shots in the recommended time-frames, B.C. is delaying second doses by up to a week or two past manufacturers’ guidelines, and Quebec is going even further, waiting up to three times longer.
The goal is to vaccinate as many people as quickly as possible, but there are still questions over just how effective these vaccines will be if policymakers stray too far from the guidelines.
What is the recommended dosing approach?
Official guidelines say the Pfizer-BioNTech vaccine is meant to be given as two doses, 21 days apart, while Moderna recommends spacing doses 28 days apart.
Canada’s National Advisory Committee on Immunization, a federal body made up of scientists and vaccine experts, says every effort should be made to follow those dosing schedules.
But, since vaccine shipments are still trickling in, the panel offered some wiggle room — suggesting the second dose for either vaccine could be delayed up to six weeks at the most.
“The flexibility provided by a reasonable extension of the dose interval to 42 days where operationally necessary, combined with increasing predictability of vaccine supply, support our public health objective to protect high-risk groups as quickly as possible,” reads a statement released Thursday from Dr. Theresa Tam, chief public health officer of Canada, and the country’s provincial and territorial chief medical officers of health.
Why are two doses, at a specific interval, even necessary?
The official guidelines for dosing intervals are based on each manufacturer’s clinical trial data, showing that the vaccines were most effective sometime after people got both rounds.
Vaccine efficacy for Pfizer-BioNTech’s option was around 95 per cent after both doses; for Moderna’s it was around 94 per cent following the second dose. (Certain high-risk groups weren’t part of those clinical trials, however, including anyone pregnant or immunocompromised.)
While research suggests there may be some level of protection from even just one shot, the consensus in Canada is that following guidelines based on the clinical trial data — as closely as possible — is the best bet to ensure people are protected.
“We also do not know how long lasting the protection will be,” said Dr. Howard Njoo, Canada’s deputy chief public health officer, during a briefing on Thursday.
“We know it’s better with two doses, but with one single dose, we are not sure.”
WATCH | : Dr. Howard Njoo discusses spacing vaccine doses out 42 days:
Canada’s Deputy Chief Public health officer, Dr. Howard Njoo, addresses questions on whether the first and second dose of COVID-19 vaccine can be safely administered 42 days apart. 2:34
So can you get sick from COVID-19 if you only get one dose?
Potentially, yes.
Clinical trials showed the level of protection from just one dose is lower for both vaccines, and it also takes time for your body to react — meaning you aren’t protected immediately after getting a shot.
The highest level of efficacy reported for Pfizer-BioNTech’s vaccine started a week after people got their second dose, and after at least two weeks following the second dose of the Moderna option.
In Quebec, health officials are currently examining how multiple residents of a long-term care home fell ill with COVID-19, despite being among the earliest in that province to receive a first round of the Pfizer-BioNTech vaccine.
That prompted questions over when the residents were infected, and Njoo noted the individuals may have already contracted the virus before getting vaccinated at all.
Long-term research will be helpful in confirming just how much protection people get from one dose of either of the approved two-dose vaccines, and how long it’s safe to delay the second shot.
Why are different regions handling dosages differently?
Some provinces, such as Manitoba and Saskatchewan, are sticking with the dosing schedule set out by the vaccine manufacturers.
But since federal recommendations suggest delaying a second dose up to 42 days at the most, other regions are considering a looser approach.
Quebec — one of the country’s hardest-hit provinces for COVID-19 cases — is stretching the dosing time-frame to a maximum of 90 days.
The province’s Health Minister Christian Dubé stressed it’s about protecting as many people as possible with a first dose before April, when vaccine shipments from Ottawa are expected to ramp up.
Njoo acknowledged some regions may be reacting to the realities on the ground.
“The pandemic has intensified,” he said. “And there are more hospitalizations and deaths.”
Quebec Health Minister Christian Dubé says a second dose of a COVID-19 vaccine may be delayed from 42 to 90 days to allow more vulnerable people to receive their first shot. 1:05
Should you get doses of different vaccines?
It’s ideal for people to be given two doses of the same vaccine rather than mixing and matching, Njoo said.
That’s because without long-term research, federal officials are again stressing the need to stick as closely to the guidelines as possible, since clinical trials are the best-available data on how to ensure these vaccines are as effective as they can be at warding off COVID-19.
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Interior Health says it delivered nearly 800,000 immunization doses last year — a number almost equal to the region’s population.
The released figure of 784,980 comes during National Immunization Awareness Week, which runs April 22-30.
The health care organization, which serves a large area of around 820,000, says it’s using the occasion to boost vaccine rates even though there may be post-pandemic vaccine fatigue.
“This is a very important initiative because it ensures that communicable diseases stay away from a region,” said Dr. Silvina Mema of Interior Health.
However, not all those doses were for COVID; the tally includes childhood immunizations plus immunizations for adults.
But IHA said immunizations are down from the height of the pandemic, when COVID vaccines were rolled out, though it seems to be on par with previous pre-pandemic years.
Interior Health says it’d like to see the overall immunization rate rise.
“Certainly there are some folks who have decided a vaccine is not for them. And they have their reasons,” said Jonathan Spence, manager of communicable disease prevention and control at Interior Health.
“I think there’s a lot of people who are hesitant, but that’s just simply because they have questions.
“And that’s actually part of what we’re celebrating this week is those public health nurses, those pharmacists, who can answer questions and answer questions with really good information around immunization.”
Mima echoed that sentiment.
“We take immunization very seriously. It’s a science-based program that has saved countless lives across the world and eliminated diseases that were before a threat and now we don’t see them anymore,” she said.
“So immunization is very important.”
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The U.S. Food and Drug Administration said Tuesday that samples of pasteurized milk had tested positive for remnants of the bird flu virus that has infected dairy cows.
The agency stressed that the material is inactivated and that the findings “do not represent actual virus that may be a risk to consumers.” Officials added that they’re continuing to study the issue.
“To date, we have seen nothing that would change our assessment that the commercial milk supply is safe,” the FDA said in a statement.
The announcement comes nearly a month after an avian influenza virus that has sickened millions of wild and commercial birds in recent years was detected in dairy cows in at least eight states. The Agriculture Department says 33 herds have been affected to date.
FDA officials didn’t indicate how many samples they tested or where they were obtained. The agency has been evaluating milk during processing and from grocery stores, officials said. Results of additional tests are expected in “the next few days to weeks.”
The PCR lab test the FDA used would have detected viral genetic material even after live virus was killed by pasteurization, or heat treatment, said Lee-Ann Jaykus, an emeritus food microbiologist and virologist at North Carolina State University
“There is no evidence to date that this is infectious virus and the FDA is following up on that,” Jaykus said.
Officials with the FDA and the USDA had previously said milk from affected cattle did not enter the commercial supply. Milk from sick animals is supposed to be diverted and destroyed. Federal regulations require milk that enters interstate commerce to be pasteurized.
Because the detection of the bird flu virus known as Type A H5N1 in dairy cattle is new and the situation is evolving, no studies on the effects of pasteurization on the virus have been completed, FDA officials said. But past research shows that pasteurization is “very likely” to inactivate heat-sensitive viruses like H5N1, the agency added.
Matt Herrick, a spokesman for the International Dairy Foods Association, said that time and temperature regulations for pasteurization ensure that the commercial U.S. milk supply is safe. Remnants of the virus “have zero impact on human health,” he wrote in an email.
Scientists confirmed the H5N1 virus in dairy cows in March after weeks of reports that cows in Texas were suffering from a mysterious malady. The cows were lethargic and saw a dramatic reduction in milk production. Although the H5N1 virus is lethal to commercial poultry, most infected cattle seem to recover within two weeks, experts said.
To date, two people in U.S. have been infected with bird flu. A Texas dairy worker who was in close contact with an infected cow recently developed a mild eye infection and has recovered. In 2022, a prison inmate in a work program caught it while killing infected birds at a Colorado poultry farm. His only symptom was fatigue, and he recovered.
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The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Science and Educational Media Group. The AP is solely responsible for all content.
Canada is about where it should be when it comes to childhood vaccines, but for adult vaccinations it’s a different story.
Dr. Vivien Brown of Immunize Canada says the overall population should have rates of between 80 and 90 per cent for most vaccines, but that is not the case.
She says most children are in that range but not for adult vaccines and ultimately the most at-risk populations are not being reached.
She says the population is under immunized for conditions such as pneumonia, shingles, tetanus, and pertussis.
Brown wants people to talk with their family physician or pharmacist to see if they are up-to-date on vaccines, and to get caught up because many are “killer diseases.”
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