Already, those infected with the first Omicron variant are 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 go on to have third or fourth infections, even within this year, researchers said in interviews.

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

It’s difficult to quantify how frequently people are reinfected, in part because many infections are now going unreported.

Pulliam and her colleagues have collected enough data in South Africa to say that the rate is higher with Omicron than seen with previous variants.

While studying common-cold coronaviruses, “we saw people with multiple infections within the space of a year,” said Jeffrey Shaman, an epidemiologist at Columbia University in New York.

But in September, the pace of reinfections in South Africa seemed to pick up and was markedly high by November, when the Omicron variant was identified, Dr.

An infection with Omicron produces a weaker immune response, which seems to wane quickly, compared with infections with previous variants.

Although the newer versions of the variant are closely related, they vary enough from an immune 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 are reinfected with new versions of Omicron will not become seriously ill.

It’s too early to know how often an Omicron infection leads to long Covid, especially in vaccinated people