How often can you be reinfected with the coronavirus?

A virus that shows no signs of going away, variants that are adept at bypassing the body’s defenses, and waves of infections occurring two or possibly three times a year. Some scientists fear that now is the future of Covid-19.

The fundamental problem is that the coronavirus has become more adept at reinfecting people. People who have contracted the first variant of omicron already report second infections with newer versions of the variant: BA.2 or BA2.12.1 in the United States, BA.4 and BA.5 in South Africa.

Scientists have said in interviews that these people could be infected for a third or even a fourth time this year. And a small portion of them may have symptoms that continue for months or years, a condition known as persistent Covid.

“I think this is likely to become a long-term pattern,” commented epidemiologist Juliet Pulliam of Stellenbosch University in South Africa.

“The virus will continue to evolve. And there will likely be many people who will be reinfected many times over their lifetime.”

It is difficult to quantify how often people are reinfected, in part because today so many Covid cases go unreported. Pulliam and his colleagues have already collected enough data in South Africa to say that the rate of reinfection is higher with the omicron than with previous variants.

It is not what was predicted. At an earlier stage of the pandemic, experts thought that immunity achieved through vaccination or previous infection with the coronavirus would prevent reinfections.

The omicron threw those hopes to the ground. Unlike earlier variants, the omicron and its many descendants appear to have evolved in ways that partially circumvented immunity. This leaves everyone vulnerable to multiple infections, even those who have received multiple doses of vaccine.

“If we continue to manage the problem as we are doing now, most people will be infected at least twice a year,” said virologist Kristian Andersen of the Scripps Research Institute in San Diego. “I’ll be very surprised if that’s not what will happen.”

The new variants have not changed 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 shot, like a previous infection, does seem to reduce the chances of reinfection — but not by much.

When the pandemic began, many experts based their expectations of the coronavirus on influenza, the viral adversary they knew best. They predicted that, as with the flu, there could be a major outbreak every year, probably in the fall. The best way to minimize the spread of the virus would be to vaccinate the population before it arrives.

Instead, however, the coronavirus is behaving more like four of its closest “cousins” that circulate and cause colds year-round. When he studied the coronaviruses that cause the common cold, said Jeffrey Shaman, an epidemiologist at Columbia University in New York, “we saw people with multiple infections within a year.”

If reinfection ends up becoming the usual pattern, he said, the coronavirus “is not just going to be this once-a-year, winter thing, and it’s not just going to be a mild little problem in terms of the morbidity and mortality it causes.”

With earlier variants, including delta, reinfections did occur but were relatively infrequent. In September, however, the frequency of reinfections in South Africa appears to have gone up, and by November, when the omicron was identified, it was clearly high, Pulliam said.

Re-infections may draw even more attention in South Africa, as well as in the United States, because so many people in these countries have already been immunized or infected at least once.

“Perception amplifies what is actually happening biologically,” Pulliam said. “It’s just that there are more people who can be reinfected.”

Omicron was different enough from delta, and delta different enough from earlier versions of the virus, that some reinfections were predictable. But now the omicron appears to be developing new forms that penetrate immune defenses with relatively few changes to its genetic code.

“That surprised me, actually,” commented virologist Alex Sigal, from the Africa Institute for Sanitary Research. “I thought we would need an entirely new variant to escape this one. But in reality, it appears that this is not the case.”

An infection with the omicron causes a weaker immune reaction that appears to lose strength in a short time, compared to infections with earlier variants. Although the newer versions of the variant are closely related, they are sufficiently different from an immune perspective that infection with one of them does not protect a person much against the others — and certainly not after three or four months.

Even so, the good news is that most people reinfected with new versions of the omicron will not become seriously ill. At least for now, the virus hasn’t figured out a way to bypass the immune system completely.

“I think it’s the best we can hope for for now,” Sigal said. “The great danger can come when the variant is completely different.”

Even so, each infection can bring the possibility of lingering Covid, the constellation of symptoms that can persist for months or years. It is still too early to know how often an omicron infection leads to persistent Covid, especially in vaccinated people.

To keep up with the virus, other experts said, Covid vaccines need to be updated faster, even faster than annual flu shots. Even an imperfect match with a new version of the coronavirus will boost immunity and bring some protection, they say.

“Every time we think we’ve got this problem behind us, every time we think we’ve mastered the problem, the virus trips us up,” Andersen said. “The way to get this under control is not to say, ‘Let’s all get infected a few times a year and hope everything goes well’.”

_{Translation by Clara Allain}