NACI reviews research showing only one vaccine dose may be necessary for those previously infected with COVID

According to a statement released by NACI, they are "actively reviewing evidence on the protection offered by one dose for those previously infected, and whether a second dose continues to be necessary."

NACI Chair Dr. Caroline Quach-Thanh said that the issue is being "debated" at the advisory committee, noting that "France and Quebec have said only one" dose is necessary for those who have previously been infected with coronavirus.

According to one letter written by 32 researchers for the New England Journal of Medicine, the issue "requires investigation," citing their own research suggesting that those who have already had coronavirus may produce up to 45 times as many antibodies upon their first vaccine dose as those who have not previously been infected. The study discusses the Moderna and Pfizer vaccines, but not ones produced by AstraZeneca or Johnson & Johnson.

Quach-Thanh also noted, however, that those who have already suffered from coronavirus may also experience worse side effects from the vaccine than typically seen in recipients. Side effects of the vaccines include mild fever, nausea, headaches, and fatigue.

"The question that remains is: is that true for everyone or at least for the vast majority?" Quach-Thanh said.

British Columbia's chief health officer, Dr. Bonnie Henry, also agrees that the issue needs more investigation. "The jury is still out but more and more it is looking like they get a really strong booster effect from a single dose and a second booster may not be necessary," she noted.

Quebec public health director Dr. Horacio Arruda made similar remarks earlier this week, going even further by saying that such patients receiving two doses "doesn't give more immunity, and it brings more significant adverse effects."

Experts largely agree, however, that despite the worse side effects, there is still no long-term harm in someone who had previously been infected with coronavirus receiving two vaccine doses.

Quach-Thanh warned, however, that this is not the case across the board, explaining that the level of protection a person may have may depend upon the severity of their previous coronavirus illness and how much antibodies they developed from it. She also said that antibodies are not a perfect method of determining the level of protection a person has against coronavirus.

"Some people without much antibodies will have protection, while others with antibodies may not be that well protected," she explained.

Dr. Fiona Brinkman of Simon Fraser University noted that not all antibodies are created equal, saying "the most important thing is to have these certain antibodies - what we call neutralizing antibodies - that we really want."

Another issue she noted is the longevity of antibodies, regardless of whether you already had the virus or received the vaccine.

"This disease literally hasn't been around long enough to allow us to appropriately assess how long you have antibodies and an immune response that will be effective against this virus, if you've either been vaccinated or you've had the disease," Brinkman said.

Regardless, Brinkman said that the research is "good news" as it could mean that Canadians could be vaccinated more quickly than previously thought.