Is a vaccine that blocks COVID-19 altogether possible?

With COVID-19 cases in Nova Scotia hitting all-time highs this week and an announcement about second booster doses for people over 70 coming soon, more prevention and protection measures are ahead — including a possible nasal spray.

Immunologist Dr. Dawn Bowdish, the Canada research chair in aging and immunity at McMaster University, spoke to CBC's Information Morning on Friday.

The interview has been shortened for edited and clarity.

Why don't current vaccines stop transmission of COVID-19?

Most vaccines don't create what we call sterilizing immunity, which means that you absolutely never carry that virus ever again. Your body does not carry it. So if we think about the ones that do — measles would be a good example — but most [vaccines] don't.

So to level set our expectations, it's not normal for a vaccine to be able to completely train the immune system in such a way that virus doesn't even get a start. And, as a consequence, even if you are vaccinated —and we're certainly seeing this in the context of Omicron — you can still get the virus, carry the virus and pass on the virus.

Certainly if everyone was vaccinated and totally up to date on their vaccination, the frequency with which carrying that and transmitting it happens is lower. But we should set our expectations to something reasonable.

I think being up to date [on vaccinations] keeps you from getting sick. It shortens the time you're sick. It reduces the chance of you transmitting to your family members time off work, reduces long COVID.

Is there any point at all then in the scientists working with Moderna and Pfizer to try to come up with a vaccine that can prevent transmission? Or is that just scientifically impossible? 

There actually is a hopeful note here, and I so rarely get to share hopeful notes that I hope you'll allow me to enjoy it. There was a couple of studies that came out of people who were what we call "highly exposed but zero negative."

So these are people who — especially in the early part of the pandemic — maybe didn't have access to personal protective equipment (PPE) and all those other things that stop infections and yet they didn't get sick. These people were health care workers predominantly.

And so a very thorough investigation of these people said what parts of their immune system were already trained to see this virus, even though it's it's was not something that they'd seen before.

And as it turns out, some previous exposure to what we call the "seasonal coronaviruses" like common cold ones, seems to have trained their immune system to recognize a really unique part of the virus, one that's not in our current vaccines.

So immunologists get very excited when we find that sort of thing out because it gives us a hint about what we should be targeting. And in fact, if you've heard about the inhaled vaccine from McMaster, it has two advantages: It's targeting this cellular immunity that has been shown to actually stop infections in their tracks. And because it's inhaled, it's putting the immune system in the right place in the right time.

We have hope that we will be able to get to a vaccine, that that will stop transmission. 

Tell me everything you know about this nasal spray. How will it work?

There's two different ideas. There's one where we actually put a drug in our nose, an antiviral drug that sort of stops transmission. Or there are other antivirals.

For example, say there was an outbreak at your kid's school or at the local long term care home or whatever. Everyone who is in close contact might take one of these antiviral drugs or these nose sprays and then hopefully be protected.

The second option are these inhaled vaccines, which come in like an asthma inhaler kind of thing, and you breathe them in very much like an asthma inhaler. And because they stimulate the immune system in the lungs and all those good antibodies and T-cells and all these wonderful immune cells are really active at the right place. The hope is they'll stop the infection in its tracks before it even get started.

So there's two up-and-coming options. I am not particularly hopeful that we'll see anything before 2023, so I don't at least I don't think we should get too excited about them yet. And you have to keep using masks and the current vaccines that we have until then. 

Are more vaccines, more boosters in our future before these booster sprays are on the market?

I was so hoping that if we could get through the first Omicron wave, we might be able to hold out a hold back to the second Omicron variant until we had Omicron-specific vaccines. We're expecting the clinical trials for those to be announced in the summer or early fall. But, of course, the virus is in charge and it had other ideas for us.

I think the important message for people to understand is that our current vaccines, even though they're imperfect, they work really, really well at shortening the symptoms, reducing the risk, etc. It just don't work for very long.

And so until we get either these universal vaccines, these new drugs and these nasal sprays, or these new Omicron-specific vaccines, it does look like we have a bunch of boosters in our future. 

The Nova Scotia government announced people over 70 will soon be eligible to get a second booster dose of vaccine. When do you think the rest of the population will be eligible?

So older adults tend to have three-to-four good months of protection. And so that's why they're being prioritized first. The general public, if it was pre-Omicron, would have had much longer. But with Omicron, it's more like four-to-seven months of good protection. And the fact of the matter is — because it looks like we're all going to get Omicron — you want that infection to be right after a nice, fresh booster. It means that your symptoms will be less a lot less chance of long-term health issues. So I think part of the decision is, who's the most vulnerable? But then the second part of the decision is how can we mitigate and stop the spread of this? Stop workplace absences, keep schools open, keep health care running. And that's by getting everyone a fresh dose to help minimize the amount of disruption we have.