Well, it means we never get “herd immunity” because people who’ve had it before can still pass it along to the vulnerable. It may mean a vaccine won’t provide herd immunity, either.
It’s not all that surprising, because it’s been known for a while that people tend to catch the common coronaviruses that cause the common cold more than once. I read two pretty careful studies of that. In one of them, the people who were re-infected didn’t get sick, in the other, some of them did “catch a cold” again from the same virus.
Also, this is the first time they’ve done genetic studies to prove it was a new infection, but there have been stories from early in the pandemic of people recovering and then testing positive again.
Yeah, genetic studies prove it was a new infection, and not a recurrence of the first one.
…says Columbia University virologist Angela Rasmussen. “I disagree that this has huge implications across the board for vaccines and immunity,” she wrote in an email, because the patient described in the study may be a rare example of people not mounting a good immune response to the first infection.
Mark Slifka, a viral immunologist at Oregon Health & Science University, says his takeaway from the paper is the opposite of what the authors write: “Even though [the patient] got infected with a very different strain that’s distinct from the first time around, they were protected from disease,” he says. “That is good news.”
…epidemiologist Maria Van Kerkhove of the World Health Organization warned against jumping to conclusions. “We need to look at this at a population level,” she said. Given that there have been more than 24 million reported SARS-CoV-2 infections worldwide, a single reinfection report may signal a very rare event, Barrett says. “Biology is complicated. You always find some strange exceptions.”
Whether reinfected people can still spread the virus may turn out to be the crucial question, Houldcroft says. “If they don’t shed and they’re dead ends, that’s fine. If they are still infectious, that’s a bit more of a problem.” Whether the Hong Kong case was infectious after his second brush with SARS-CoV-2 is not clear; the researchers are trying to culture live virus from the patient, To says. “But viral culture takes some time, so we don’t know yet.” Given the experience with other respiratory viruses, Slifka says he would expect the patient to be about 10 times less infectious the second time around.
That last bit seems to me to indeed be a key item, especially if those who are re-infected overwhelmingly get mild to asymptomatic illness: whether reinfected people can still spread the virus.
As has been discussed on this board before, 10% of those infected seem to be responsible for 80% of the spread and 70% never spread to another single soul. If having been previously infected means that subsequent disease is mild and much more likely to be within that 70% non-spreader group, that would be very very good news. Even if the are able to culture viable virus the question of how effectively they can spread it is not resolved.
Not sure why Slifka expects a reinfection to be 10 times less infectious the second time around but could be.
I agree with the potential good news of this in terms of vaccines. A response to one strain protecting an infection with a different from becoming significant disease would be very hopeful that protection from illness will be long lasting, and the impact on transmissibility is going to be key to determine over time.
To expand on this, various different parts of a pathogen may be recognized as non-self, so in one individual the first infection may result in numerous different clones of memory cells that recognize different epitopes that are present in that virus. (And note that with widely variable genetics in the immune system, there may be wide variation in response in the population - different people may acquire immunological memory for different parts of a virus.)
With a second strain, some of the parts that were recognizable as non-self in the first strain may be identical in the second strain, some may have mutated to change shape partially, some may be deleted and completely absent. So immunity to reinfection depends not only on whether immunological memory has weakened over time, but on all these other potential sources of variation in exactly what the immunological memory in a given individual is primed to respond to.
The partial response in this patient that allowed reinfection but protected from disease may be attributable to immunological memory fading over time, but it may also be attributable to differences in the second strain. And the point made by Mark Slifka in the Science article is that it may be good news that the response was robust enough at least to prevent serious symptoms when reinfected with a different strain.
We don’t know exactly what happened in this one individual; and even if we did, a sample of one tells us virtually nothing new about the typical response that we can expect in the population as a whole, since it was never unexpected that reinfection was possible in some cases.
Just trying to think this thing through fully. If protection lasted for something like six months on average, wouldn’t we expect to start seeing reinfection only right about now?
To recap - questions that need answers for both natural disease and any potential vaccination include:
What fraction are completely protected after infection/vaccination and what is the range of how long (with wha sort of variation about the mean)?
What fraction are how much protected from severe disease if they are in fact still susceptible to infection?
How effective of transmitters are those who are infected after primary infection/vaccination? (Nasal carriage may not be a good proxy of that.)
The FDA has stated that they will approve a vaccine that reduces the risk of infection by 50% for at least the short term. Infection is the primary end-point but a lesser decrease in actual significant disease might warrant approval. The impact of transmissibility is not part of the requirement, nor duration of protection. And a safe vaccine meeting those criteria would still be of huge impact.
A few tens of thousands getting mild disease to asymptomatic infection with reinfection would not impact the odds of meeting those criteria much.
It only means that if reinfection is possible in a large percentage of the population. According to Wikipedia, we can get herd immunity to this thing if 50-83% of the population is rendered immune. So if only a couple percent of the population are susceptible to reinfection, it’s not likely to be a big deal.
Where herd immunity is concerned, I think the bigger threat by far is going to be people who refuse to take the vaccine.