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Welcome to the Great Reinfection

Grace Browne wrote . . . . . . . . .

If you are unfortunate enough to have had an intimate encounter with the dreaded Sars-CoV-2 virus, I’m afraid your dalliance with it might not have been your last. Get ready for round two (and three, and maybe four—maybe ad infinitum). Welcome to the Great Reinfection.

In the early months of the pandemic, reinfections were a remarkable rarity, even making global news when discovered. “When the pandemic first started, everybody assumed that once you got it, you were done,” says Juliet Pulliam, director of the South African DSI-NRF Centre for Epidemiological Modelling and Analysis at Stellenbosch University.

Two years and some change in, that novelty has largely evaporated. A perfect storm of waning immunity, loosened restrictions, and an extremely transmissible variant making the rounds has meant reinfections are the new normal for many. But even setting aside these factors, it makes sense that there are now more reinfections than ever. At this stage of the pandemic, repeat infections would always have been more common than before, owing to the sheer number of people who’ve had Covid-19. You can’t get reinfected unless you’ve already been infected in the first place.

Beyond that basic math, it’s not really surprising that reinfections are happening, says Aubree Gordon, an infectious disease epidemiologist at the University of Michigan. “The virus has changed a lot,” she says. If you were infected with an earlier variant, Omicron is like that variety wearing a wig and makeup—making it largely unrecognizable to our bodies’ immune defenses and harder to stave off.

But if reinfections are now part and parcel of the future of the pandemic, just how common are they? An exact number is hard to pin down, thanks to a nosedive in testing and reporting that has made tracking all kinds of Sars-CoV-2 infections much trickier. Plus, not everyone defines a reinfection the same way; health authorities in the UK, for example, require at least 90 days to elapse between a first and second infection for this to count as a reinfection. Others, like the European Centre for Disease Prevention and Control, use a shorter 60-day minimum between infections.

In England, close to 900,000 possible reinfections have been identified since the beginning of the pandemic. Of those, over 10,000 were a third infection, and almost 100 were a fourth.

Pulliam’s own work has tried to put a number on how many infections are actually reinfections. She and her team found that as of last week, around 15 percent of current infections in South Africa are reinfections. “And that is almost certainly an underestimate,” she cautions, “because our surveillance isn’t great, and we probably missed a lot of people’s first infections.” But to answer just how prevalent reinfections are—in the grand scheme of things—Pulliam uses two words to sum it up: fairly rare.

She and her team have also investigated just how much Omicron has shaken things up. They started monitoring reinfections towards the end of the Beta wave in South Africa (which peaked in January 2021), looking at over 100,000 suspected reinfections. They found that the protection an initial infection offered against reinfection stayed the same all through the Beta wave and all through the Delta wave that peaked the following July. And then Omicron hit. The risk of reinfection steadily rose and stabilized at a higher number.

South Africa, Pulliam says, is uniquely placed to study reinfection, serving as a barometer for the rest of the world’s reinfection future, given that Omicron has already made its way through most of the population. “If what’s going on in South Africa is any indication, it’s that probably people are going to be reinfected over the course of years,” she says. Reinfection, Pulliam believes, is going to be a normal part of the way we live in the future.

Other studies have shown just how much Omicron has changed the reinfection calculation. According to data from the UK, the risk of being reinfected with Covid-19 was about eight times higher after Omicron became the reigning variant in the country compared with when Delta held the crown. Another paper from Imperial College London published in December 2021 found that Omicron was five times more likely to reinfect people than the previously dominant Delta variant.

Laith J. Abu-Raddad, an infectious disease epidemiologist at Weill Cornell Medical College in Qatar, has investigated how much a previous infection protects against a future one—and how much this has shifted because of Omicron. In a study published in March, he found that pre-Omicron, the effectiveness of a Covid infection against a reinfection hovered at about 90 percent—in both the vaccinated and unvaccinated. Post-Omicron that number dropped to about 50 percent. Reinfections, he says, “are becoming an accepted reality.”

It’s the sheer difference between Omicron and earlier variants that explains why the risk of reinfection has shot up. But the virus is still changing, so even if you’ve had Omicron, that doesn’t mean you won’t catch Covid again—and you can even get reinfected with the different manifestations of Omicron. A February preprint from researchers in Denmark suggests that the BA.2 sublineage of Omicron can reinfect people shortly after they’ve had the original BA.1 form, but the paper did conclude that such reinfections are rare. Some of those in the study were reinfected as quickly as 20 days after their initial infection, which, the authors write, calls into question just how suitable it is to use a minimum 60-day gap for classifying a case as a reinfection.

Similarly, Alex Sigal, a virologist at the Africa Health Research Institute in South Africa, has found a comparable pattern in his own research, which is also still in preprint. He and his team found that an infection with the original BA.1 version of Omicron offered little immune protection against the newer versions of Omicron, BA.4. and BA.5.

This could be a sign that the virus is beginning to mimic the natural rhythms of other coronaviruses, which infect and reinfect us many times in our lifetimes. We all come down with a coronavirus infection about every three years; sometimes even multiple times within the same year. Sars-CoV-2 could be no different. However, we don’t quite know whether these repeat infections are due to the fact that the initial infection gives us immunity that wanes posthaste, or if the viruses themselves evolve to outsmart our previously built immunological weaponry. Previous work that has attempted to answer this question leans towards the latter theory.

Knowing this, one solution to fighting all these reinfections, Sigal says, is to design a better vaccine. Moderna is already publishing data on a broader-type booster vaccine that mixes equal amounts of the spike proteins from the OG and Beta variants, which seems to work better at providing more universal coverage against the virus.

At the end of the day, the good news is, you’re not likely to get a severe case on your next tussle with the virus—in another study from Abu-Raddad, a reinfection was found to result in a 90 percent lower chance of ending up in the hospital or dying than your first infection. But you should still try not to repeat the experience. While your risk of severe disease or dying seems to be much less when reinfected, it doesn’t mean that there aren’t people who die on their second infection. “It’s not a gamble you really want to take,” warns Pulliam.

Plus, Sigal points out, “we don’t know what these repeated cycles of infection will do.” The more people harbor the virus, the more likely a variant we don’t like will emerge from the woodwork. And on an individual level, it’s possible that a second reinfection could be the one to cause long-term damage, like long Covid. Whether reinfection is, in fact, leading to long Covid is the really big question, says Pulliam. “It’s going to make a big difference in terms of whether we view it just as a cold virus going forward,” she says. “Or whether we view it as something that is really serious.”


Source : WIRED

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