COVID reinfection is possible

Doctors in Hong Kong have reported the first confirmed case of someone being re-infected with the new coronavirus. Until now it’s been an open question whether or not getting COVID and then recovering makes you immune. But this case - along with others now surfacing including a man in the US - suggests otherwise. Phil Sansom asked virologist Jeremy Rossman for his thoughts…

Jeremy - What we've seen recently from Hong Kong, and then some data in the U.S. is when the person was initially infected, they actually sequenced the virus. And then when the person was sick again, they sequenced the virus again. And by comparing the genome of those two virus samples, they were able to say that, in fact, this was not one long infection, but was an infection with two different variants of COVID-19. So we can now definitively say that in fact, reinfection is possible,

Phil - Oh God. Well, who are our unlucky winners in this horrible situation?

Jeremy - I don't actually know. That's an interesting question. I don't actually know.

Phil - I actually do, I'll give it to you. So in Hong Kong, it was a 33 year old man who got his first coronavirus in March they tested him. And then he got it again in August. And then there's this other person in Nevada. Who's a 25 year old man, but the Hong Kong guy actually didn't have symptoms the second time. But the Nevada guy got them way worse.

Jeremy - Yeah, we are very curious to know what happens in the reinfection, because this has very large implications for what happens if somebody is vaccinated. Vaccines provide a level of immunity, but some vaccines don't perfectly prevent infection. And so if somebody is reinfected and has a lower disease severity, that's a pretty good indication that vaccines might also lower disease severity. Whereas if you have a worse disease, then we might have some concerns. And we don't know if this is the case yet. From the two reinfections that we know so far, we've seen very different phenomena. In one, we've seen much more mild reinfection and in the other, we've seen a more serious reinfection,

Phil - I'm kind of impressed that you managed to find a positive thing that we can learn out of this. Because isn't this reinfection something that people have been really, really worried about?

Jeremy - It is. But we have to take this with a grain of salt, because we are looking at a tremendous number, millions of cases of coronavirus worldwide. And we are looking at the first two known cases of reinfection. So yes, this says that reinfection can occur, but this may be a vanishingly small number. This may only occur after a certain amount of time. We don't necessarily have to worry.

Phil - Do you think it'll have to do with how your immune system reacts the first time round?

Jeremy - Certainly. What we're looking at is the development of immune memory. There are two main ways in which you get immune memory. Antibodies, or B cells and T cells, and both of these can be very effective and can work together to help protect you. But the real question is how effective these immune responses are at preventing infection. So I'll give you the example of antibodies. Sometimes the antibodies aren't active enough, they don't prevent infection. Maybe they just lower disease severity. The other aspect is that just because you've formed the immune memory, this tends to decay over time. And we've seen some evidence of this. There are a lot of variables here, and we're really just starting to get the answers. And there's still a lot of data that we don't know yet.