Questions on Covid-19 reinfections still up in the air
No-one can say for sure how many times people are going to need to be infected to confer effective immunity against transmission
In October 2020, a few weeks before the experimental trial results for the BioNTech-Pfizer, Oxford/AstraZeneca Covid-19 and Moderna vaccines were released, German virologist Christian Drosten cautioned that the shots would be of limited effectiveness in preventing the spread of the disease.
“We are dealing here with an infection of the mucous membrane, that is, in the nose and the throat and then later the lungs,” he said on episode 62 of Das Coronavirus-Update, the podcast launched by broadcaster NDR in March 2020 that helped make Drosten a household name in Germany.
“The mucous membranes already have their own special local immune system. With the current vaccines, which are more likely to be injected into the muscle, you don’t reach this local immune system so well.” As a result, the vaccines “probably protect more against the severe course [of the disease] than against infection”.
Which is, of course, exactly how things played out. The vaccines have been spectacularly effective at preventing severe disease and death, much less so at preventing transmission.
With influenza, it is simply the case that everyone gets infected x times over the course of their lives. These infections occur in the mucous membrane, in the throat. Our mucous membranes have a local immune system of their own, if you want to call it that. And everyone in the population, except for the children, of course, has so many infections behind them that there in the mucous membrane, immunity exists. That is why the adults in the population, and that is the vast majority of the population, are not so infectious.
Vaccines have been spectacularly effective at preventing severe disease and death, much less so at preventing transmission
It is this mucosal immunity that keeps influenza from spreading most of the year, with the disease’s effective reproduction number (the average number of people who will get it from each one who has it) surpassing one for only a few months in winter, when indoor crowding, drier air and other factors seem to lead to increased transmission.
Contrast that with Covid-19: vaccines generate some mucosal immunity but it fades quickly, and while there are nasal-spray vaccines in development that target the mucous membrane, they’re not ready yet, and this approach has been of only mixed effectiveness against influenza. Meanwhile, less than half the German population has been infected with Covid-19, Drosten said (in the US, according to a Centers for Disease Control and Prevention report this month, it’s 57.7%), so there probably isn’t nearly enough mucosal immunity out there to prevent the reproduction number from rising back to two or three in winter, bringing another huge wave of infections and concomitant stresses on hospitals and disruption of daily life.
One thing that could preclude this, Drosten speculated, might be a lot of young people (the “party generation”, he called it, in English) getting infected a second or third time over the summer, but he expressed doubt that this would be enough to make a difference in 2022.
How many times are people going to need to be infected to confer effective immunity against transmission, asked NDR science reporter and podcast moderator Korinna Hennig. Drosten’s reply: “My idea is that this is in the range of a number that you can count on one hand. But no-one can say for sure at the moment.”
The role of infection-conferred immunity in slowing the spread of Covid has been a sensitive topic. Early in the pandemic, it was emphasised by a few scientists (and a lot of non-scientists) who wildly underestimated the deadliness of the disease. Later, after vaccines became available, anti-vaxxers argued that natural immunity was superior to the sort conferred by shots. The latter claim isn’t entirely wrong — as might be expected from Drosten’s explanations, there’s some evidence that prior infection provides better protection against subsequent infection than current vaccines do (though there’s counter-evidence, too). But it’s far less dangerous to get a shot than to get Covid for the first time, and once you’ve been infected, vaccines add significant protection against reinfection.
Relegating SARS-CoV-2 to the status of an endemic virus like the flu or the several coronaviruses that cause common colds, though, may require lots and lots of us getting the disease, again and again. As Drosten put it in an interview in January: “Over the long run, we will not be able to vaccinate the population every few months. That won’t do. At some point, the virus itself will have to keep updating people’s immunity.”
Given the source, it’s hard to argue with this. As a guide to policy and behaviour, though, it’s not so clear. Going to great lengths to avoid infection makes less sense for most of us than it used to, and trying to maintain a zero-Covid policy as a nation, as China is doing, seems to make no sense at all. But should we be going out and trying to get infected?
Drosten certainly doesn’t subscribe to this view, instead expressing hope that the “Asian courtesy” of wearing a mask when ill and in certain other situations catches on in Germany. Wondering what the right balance might be, I asked my primary-care physician (and college classmate) Bertie Bregman, who has been treating Covid patients in New York since the early days of the pandemic and contracted the disease early on, too. He had an interesting response: “In a nutshell, what I believe is that we have to stop being so neurotic about Covid and be more neurotic about everything else.”
That is, with Covid now manifesting itself among the vaccinated and those with prior infections (that is, almost everybody) mainly as a standard-issue upper-respiratory infection, we should probably just treat it as a standard-issue infection, albeit with a heightened awareness that the spread of such diseases can and should be slowed by simple measures such as staying at home and wearing a mask when sick.
The one “wild card”, Bregman allowed, is long Covid, the risk that even mild cases now could lead to complications later. But taking reasonable care around cold- and flu-like symptoms is likely to be more effective in curbing Covid, he thinks, than the widely followed approach of taking rapid Covid tests and going about life as normal if they come back negative — “then half the time a week later they turn out to be positive”.
What about building immunity? Exposing children early on to germs and allergens pays dividends later, Bregman said, but for adults “the costs of getting sick outweigh the benefits”. So yes, most of us will probably get Covid, repeatedly. No need to rush it, though.
Bloomberg News. For more articles like this please visit bloomberg.com
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