VIDO virologist explains COVID-19 vaccine protections, need for booster shots and more

Next week a third booster COVID-19 vaccine will be available to a specific group of eligible people, mostly residents of long-term care homes and those who are severely immunocompromised. 

Why are these people needing a booster shot, and will everyone need one at some point?

CBC Saskatchewan news anchor Sam Maciag talked with Alyson Kelvin, a virologist at the Vaccine and Infectious Disease Organization (VIDO) in Saskatoon, to get her thoughts on boosters and other questions about vaccines.

Here is their conversation, which has been edited for clarity and space.

Maciag: There are lots of conversations around booster shots as it's been happening in places like the United States for a while. When should people start considering getting a booster shot? 

Kelvin: I think that really depends on your unique medical status. We know that people who are immunocompromised, possibly people who are older, might not have as beneficial response to the two traditional doses of the COVID-19 vaccines. And what we're seeing is that there is data supporting a third dose of COVID-19 vaccination in people who are immunocompromised. This might boost their overall protection.

For the general public I think we don't have enough data right now to determine if a third booster shot this time is really going to add to protection. 

Maciag: How is getting a booster shot different from, say, getting an annual flu shot?

Kelvin: So these are two totally different viruses. Right now, we're in a pandemic, whereas the typical influenza virus is more seasonal, so we have to get a seasonal shot to protect us through the winter.

Right now, we're having infections basically all through our year. So we want to look at what our immune response is doing, how long our immune response lasts after vaccination to really determine when our next shot should be given. 

Maciag: As we get more and more data about how the vaccines are working in the population, what's the biggest standout for you? 

Kelvin: One of the biggest standouts to me is that there was such a high effectiveness for the MRNA vaccines in their initial clinical trials and throughout the first couple of months of usage of the vaccine. 

Typically, when we design vaccines for a respiratory virus, you know, we're aiming for 50, 60, 70 per cent. So this was a lot more than what we were typically used to for this type of virus. 

Maciag: When it comes to breakthrough cases, people who are fully vaccinated but do end up in hospital, why does that happen? 

Kelvin: These breakthrough infections are actually of more mild disease. So the vaccine is more protecting against disease than infection.

As we're getting more and more people vaccinated I do expect this effectiveness to decrease, not in how severe the disease is in someone who is vaccinated. 

I still expect that to stay around 90, 95 per cent, keeping people out of hospitals. But I do expect the effectiveness of people actually getting infected to decrease.

This is because you actually have a different immune system in your upper respiratory tract, in your nose, than you do in your lungs. So we know that when you get a needle in your arm, that induces protection that is greater in your lungs. So you're not going to have such severe disease if you get infected because the lungs aren't going to be destroyed. 

Whereas in your upper respiratory tract, it's harder to protect from infection up here through a needle that you've got in your arm.

And that's really why we're having what we're seeing with these breakthrough infections —  less severe disease, because the virus isn't infecting in the lower respiratory tract.

Maciag: We are entering this fourth wave. How does the delta variant play into all of this when it comes to vaccines? 

Kelvin: We know that there are slight differences between the virus that the vaccine was modelled after and the delta variant. 

But compared to other variants, such as the beta variant, there's actually greater protection from the vaccine against the delta variant than the beta variant. So even though there's slight differences in effectiveness for the delta variant, I still expect the original vaccine to be protective against delta and severe disease caused by infection of the delta variant.