Episode #53 - COVID-19: Booster Shots

11 September 2021 | Science conversation

Vismita Gupta-Smith

Dr. Katherine O'Brien

The second reason why we might give a third dose is if over time the immunity that you received and achieved as a result of being vaccinated starts to wane, it starts to deteriorate or go down over time. And in fact, the evidence right now shows that the vaccines are holding up extremely well to protect you against severe disease, hospitalization or even death. So we don't see strong evidence leading to a need to provide a third dose for people who have already been vaccinated. 

The third reason we might want to give a third dose is if the performance of the vaccines are less or inadequate against some of the variants of concern that have emerged. And again, the vaccines that we have right now against the variants and we're watching this very carefully are holding up extremely well against the severe end of the disease spectrum. Generally speaking, the vaccines are performing very well. 

Kate, is there a scenario where certain groups of people may need this to dose of a booster shot? 

Right now, we do have some evidence that there's a small proportion of people, those people who have serious immunocompromised conditions that don't seem to respond to the first two doses in the way that people who don't have an immunocompromised condition do what they need is they need a third dose, but that's really for their primary response. It's because they haven't adequately responded to the first two doses. But apart from the protection that a booster dose affords people, there are some other considerations we need to know. 

Does giving a third dose actually increase the immune response? And we do see evidence that that's true, and we would expect that to be true based on what we know about how vaccines work. But the other issue is, should those doses be given? As I mentioned before, the evidence is weak for making that argument. We certainly don't see conclusive evidence that a booster dose among the majority of people who have been vaccinated already is needed. And the third issue is safety. 

Giving a third dose needs to be monitored for the safety issues, and we would like to see a safety database before we would make any such recommendation. And that evidence is also building, but we're not there yet. 

But the question still remains should the world be looking at booster shots at this stage of the pandemic? 

So right now, we're in a situation where, as I said, the evidence shows that the vaccines that people have received are holding up really well to protect you against severe disease, against hospitalization and against death. And that's really the primary intent of the vaccines. What we also see is that we're in a really inequitable place right now about who has already received the first and the second doses to provide protection against the severe outcomes in low income countries and low middle income countries that they are only at about one percent, two percent, five percent of the population having received vaccine already. 

And that compares with a lot of vaccine having been deployed in high income countries and upper middle income countries. So the focus now for the supply needs to be to protect those people who are not yet protected at all by vaccines. It will reduce transmission, it will reduce the likelihood of more variants emerging, and it will give us time to see more of the evidence about whether or not booster doses will eventually be needed. Nobody is safe until we all have the opportunity to be vaccinated, to be protected against the virus while vaccine coverage is increasing. 

And what that really means is getting doses now to those parts of the world that have not had adequate supply so far. While we're doing that, it's really important to continue the other measures that reduce transmission of the virus. That includes mask wearing, hand-washing, not gathering in large crowds when you're indoors, being in well-ventilated spaces. Those are the things that, along with the vaccines, are going to protect you both from disease and from the transmission of the virus. 

And that's what the focus is right now. That's what's going to end this pandemic. 

Thank you, Kate. That was Science in 5 today. Until next time, then stay safe, stay healthy and stick with science.