Declining antibodies do not necessarily mean less protection for healthy individuals
Mark Brockman, PhD, a member of the Coronavirus Variants Rapid Response Network (CoVaRR-Net), says the number of SARS-CoV-2-fighting antibodies in our system does eventually diminish, but the jury is out on whether or not that decline means healthy people are no longer protected against infection.
Immune systems come to life when they respond to a virus: that’s when they start to make new antibodies. “The immune system is still there and ready to go. So, if you do encounter the virus later, the immune system is likely to ramp up very quickly and make all those antibodies. This is a normal part of the immune response: when the pathogens are no longer there, you don’t need the antibodies. So, they decline over time,” Brockman says.
It’s therefore hard to say, definitely, that a third dose of a COVID vaccine is necessary for fully vaccinated healthy individuals. When we measure with a blood test the number of antibodies in our system, it’s only a reflection of the immune system in a resting position, with no virus in sight.
Brockman says that people with healthy immune systems who have received two doses of the vaccine will not find much more protection from severe symptoms of COVID from a third dose. “The two doses of vaccines are doing what they’re supposed to do. I would suggest that people who have had two shots and are otherwise healthy, probably don’t need a third dose.”
For the elderly or immunocompromised, a third dose is recommended
Research from Brockman’s team and other teams across Canada and around the world have shown that older people and the immunocompromised do not produce as many antibodies after two doses as the rest of the population. What’s more, the number of antibodies decline significantly faster, leaving many older people and the immunocompromised with few antibodies at all. That’s why a third dose is being recommended for those populations. “This is to get them to a level of antibodies that would otherwise be normal in a healthy person receiving two doses.”
Indeed, Brockman says this is also why we’re seeing more breakthrough infections in the immunocompromised and older people compared to younger, healthier individuals.
Researchers must continue to keep a close eye out for changes
Vaccines are designed to protect people from severe illness and hospitalization. “So far, the vaccines are doing a fantastic job of that, even in some of these higher-risk populations. We need to keep an eye out for whether or not there are more breakthrough infections that are resulting in more severe outcomes, more people showing up in the hospital or the ICU,” says Brockman. If that happens, then there might need to be third-dose recommendations for younger and healthier parts of the population.
So far, the vaccines are doing a fantastic job of [protecting people from severe illness and hospitalization], even in some of these higher-risk populations. We need to keep an eye out for whether or not there are more breakthrough infections that are resulting in more severe outcomes, more people showing up in the hospital or the ICU.
Mark Brockman, CoVaRR-Net Pillar Lead
A universal third dose in Canada could lead to inadequate vaccinations for the developing world
“If we give every Canadian a third dose right now, we are to some degree contributing to having fewer vaccines available to the global population,” says Brockman. “Canada wants to be on the safe side and not ship all of its vaccines abroad and then have another wave of variant come through. But the flip side of that is that as long as the virus continues to affect people globally, it has a chance of adapting and mutating, with new variants arising. The best way to protect against that is to make sure that global populations are vaccinated, bring the number of infections down as much as we can and prevent the virus from replicating.”
Download a document showing the booster dose recommendations for provinces and territories in Canada as of November 11, 2021.