How often can you get infected with the coronavirus?

A virus that shows no signs of going away, variants that are adept at dodging the body’s defenses, and waves of infections twice, maybe three times a year: this may be the future of Covid-19, some scientists now fear.

The core problem is that the coronavirus has become more adept at reinfecting people. Those infected with the first Omicron variant are already reporting second infections with the newer versions of the variant: BA.2 or BA2.12.1 in the United States, or BA.4 and BA.5 in South Africa.

Those people may have a third or fourth infection, even within this year, the researchers said in interviews. And a small fraction may have symptoms that persist for months or years, a condition known as prolonged Covid.

“It seems likely to me that this will be a long-term pattern,” said Juliet Pulliam, an epidemiologist at the University of Stellenbosch in South Africa.

“The virus is going to continue to evolve,” he added. “And there are probably going to be a lot of people who get many, many reinfections throughout their lives.”

It’s hard to quantify how often people get reinfected, in part because many infections now go unreported. Dr. Pulliam and her colleagues have collected enough data in South Africa to say that the rate is higher with Omicron than with previous variants.

This is not how it was supposed to be. Early in the pandemic, experts thought that immunity from vaccination or previous infection would prevent most reinfections.

The Omicron variant shattered those hopes. Unlike previous variants, Omicron and his many descendants appear to have evolved to partially bypass immunity. That leaves everyone, even those who have been vaccinated multiple times, vulnerable to multiple infections.

“If we handle it like we do now, most people will get infected at least a couple of times a year,” said Kristian Andersen, a virologist at the Scripps Research Institute in San Diego. “I would be very surprised if that’s not how it’s going to play out.”

The new variants have not altered the fundamental utility of Covid vaccines. Most people who have received three or even just two doses will not get sick enough to need medical attention if they test positive for the coronavirus. And a booster dose, like a previous bout with the virus, seems to lower the chance of re-infection, but not by much.

At the start of the pandemic, many experts based their expectations of the coronavirus on influenza, the viral enemy most familiar to them. They predicted that, as with the flu, there could be a big outbreak every year, most likely in the fall. The way to minimize their spread would be to vaccinate people before they arrive.

Instead, the coronavirus is behaving more like four of its closely related cousins, circulating and causing colds throughout the year. While studying common cold coronaviruses, “we saw people with multiple infections in the space of a year,” said Jeffrey Shaman, an epidemiologist at Columbia University in New York.

If reinfection turns out to be the norm, coronavirus is “not just going to be a once-a-year thing over the winter,” he said, “and it’s not going to be a mild nuisance in terms of the amount of morbidity and mortality.” cause.”

Reinfections with earlier variants, including Delta, did occur but were relatively rare. But in September, the rate of reinfections in South Africa seemed to pick up and was notably high in November, when the Omicron variant was identified, Dr Pulliam said.

Reinfections in South Africa, like in the United States, may seem even more noticeable because many have already been vaccinated or infected at least once.

“Perception magnifies what is actually happening biologically,” said Dr. Pulliam. “It’s just that there are more people who are eligible for reinfection.”

The Omicron variant was different enough from Delta, and Delta from previous versions of the virus, to expect some reinfections. But now, Omicron appears to be developing new forms that penetrate immune defenses with relatively few changes to their genetic code.

“This is really a bit of a surprise to me,” said Alex Sigal, a virologist at the African Health Research Institute. “I thought we’re going to need some sort of completely new variant to escape this one. But in fact, it seems you don’t.

An infection with Omicron produces a weaker immune response, which appears to decline rapidly, compared to infections with earlier variants. Although the newer versions of the variant are closely related, they vary enough from an immunological perspective that infection with one doesn’t leave much protection against the others, and certainly not after three or four months.

Still, the good news is that most people who get reinfected with new versions of Omicron will not get seriously ill. At least for now, the virus hasn’t found a way to completely bypass the immune system.

“That’s probably the best there is for now,” Dr. Sigal said. “The big danger could arise when the variant is completely different.”

Each infection can bring with it the possibility of a long Covid, the constellation of symptoms that can persist for months or years. It is too early to know how often an Omicron infection leads to prolonged covid, especially in vaccinated people.

To keep up with the evolution of the virus, other experts said, Covid vaccines need to be updated more quickly, even faster than flu shots each year. Even an imperfect match with a new form of coronavirus will still amplify immunity and offer some protection, they said.

“Any time we think we’re over this, every time we think we have the upper hand, the virus tricks us,” Dr. Andersen said. “The way to control it is not, ‘Let’s get infected a few times a year and then hope for the best.'”

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