Although the U.S. will soon offer COVID-19 vaccine booster shots to the general population, Canadian experts aren’t sure that Canada should follow suit.
The U.S. Centers for Disease Control and Prevention made the announcement Wednesday that they are planning to offer a third dose of the Pfizer and Moderna vaccines to Americans, eight months after they had their second dose.
They expect to start offering booster shots to people in September, as Americans who received their shots first become eligible. The overall plan is awaiting a Food and Drug Administration evaluation of the safety and effectiveness of a third dose, the officials said.
The CDC decision was expected, said Alyson Kelvin, a Canadian vaccinologist who works with the Vaccine and Infectious Disease Organization in Saskatoon, but she’s not sure it’s the right one. “Looking at the evidence, I think that many scientists are conflicted whether or not the general public does need booster shots,” she said.
The CDC points to three pre-print studies released Wednesday that examined how well vaccines protected against infection and hospitalization with COVID-19 in the real world. However, all three studies measure vaccine effectiveness over a period before and after the Delta variant became the predominant COVID-19 variety in the U.S..
In other words, it’s hard to tell from these studies whether increasing case numbers are due to people’s immunity fading over time, or whether it’s due to vaccines being less effective against the Delta variant.
“This study could not differentiate the independent impact of the Delta variant from other factors, such as potential waning of vaccine-induced immunity,” reads one study, which examined people in nursing homes. “Further research on the possible impact of both factors on VE (vaccine effectiveness) among nursing home residents is warranted.”
To some leading scientists, the studies “would not be sufficient, in and of themselves, to make the case for a booster,” said Dr. William Schaffner, an infectious-diseases expert at Vanderbilt University, and a liaison to an expert advisory panel that helps the CDC form its vaccination recommendations.
Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, noted that other studies looking at antibodies suggest that immunity fades over time and higher antibody levels might be needed to combat the Delta variant. Giving a third dose causes a “dramatic increase” in antibody levels, he said.
Even though it is calling for a booster shot, the CDC emphasized that the vaccine remained effective against catching COVID-19 and helped prevent serious outcomes from the disease. “While we are still learning about how these vaccines perform over time and how long they will last against emerging variants, one thing is very clear: Getting vaccinated can keep you out of the hospital. Getting vaccinated can save your life,” said CDC director Dr. Rochelle Walensky.
In recent weeks, several other countries have decided to offer booster shots to older adults and people with weak immune systems, including Israel, Germany and France. European Union officials said on Wednesday they do not yet see a need to give booster shots to the general population.
Read more: Ontario giving 3rd COVID-19 vaccine dose to high-risk people. What about other provinces?
“I think that there’s some evidence that immunity does wane,” Kelvin said. “This happens with all vaccines or even infections.”
When it comes to new variants though, Kelvin isn’t sure how much a third dose of the exact same vaccine will help. “Is this a boost of the same vaccine or is this a boost that’s matching the most prominent circulating variant?” she asked.
If your antibodies are different from the circulating virus, “It doesn’t matter if you get another vaccine to the original SARS-CoV-2 spike protein because it’s a mismatch already,” she said.
Reaching the right people
The Public Health Agency of Canada didn’t respond to specific questions about the CDC decision by deadline, however it noted that people in specific populations who are immunosuppressed might not mount as strong a defence against the virus as others after they get vaccinated. The National Advisory Council on Immunization is reviewing evidence for a booster shot in this population, PHAC said, and will update its recommendations “in the coming weeks.”
People who take immunosuppressant drugs, such as organ transplant patients who take them so they don’t reject their new organs, often have weaker responses to vaccines, said Dr. Deepali Kumar, director of transplant infectious diseases at the University Health Network in Toronto.
“It’s not surprising that that the response to mRNA vaccines would be low in immunocompromised people, and third doses seem to somewhat overcome that problem,” she said. “If a transplant patient gets COVID, they are more likely to end up in the hospital, more likely to end up in the ICU and more likely to die. And so this is a population that we really need to protect.”
Ontario recently announced that it will give booster shots to certain at-risk populations, and other provinces are considering similar measures.
Until we have more specific data though, Kelvin thinks that Canada’s vaccination focus shouldn’t be on giving third doses to fully-vaccinated people in the general population.
“Helping vaccines reach underserved communities in North America is really going to help us achieve our goal of reducing COVID-19 infections,” she said. She thinks it’s more important to reach people who haven’t gotten their first and second doses.
“My perspective as a vaccinologist would be: trying to get as much vaccine coverage both in areas of North America as well as all over the world, is going to help bring down the virus circulating and the number of COVID-19 cases that we’re seeing.”
Kumar agrees. “We need to focus on making sure that the first and second doses are in people’s arms first,” she said. “I mean, we still have a good proportion of the younger population that hasn’t had their first or second doses. So I think, if we’re going to stop the pandemic, we need to cast a broad net and make sure that that everyone’s vaccinated.”
-with files from the Associated Press