Reinfection in Omicron patients unlikely for now: Experts

SINGAPORE - The chances of someone who had the Omicron variant of Covid-19 getting reinfected are quite slim at present, experts told The Straits Times.

The experts also said that reinfection in someone who had Omicron is less likely than in someone who had another, earlier variant of the virus, and that time plays an important factor in determining reinfection risk. But either way, vaccines remain key to reducing risk of severe illness and death, they said.

Associate Professor Hsu Li Yang, vice-dean of global health at the National University of Singapore (NUS) Saw Swee Hock School of Public Health, said the risk of getting reinfected with the BA2 subvariant - one of the two major Omicron subvariants - is extremely low at the moment. 

“The Omicron variant has been in Singapore for only a few months, so anyone here would at most have gotten infected with Omicron only two to three months ago. The risk of a Covid-19 reinfection within six months is generally extremely low,” he explained.

The risk of getting reinfected by the same strain of Omicron is also likely to be negligible within the first year, added Prof Hsu, but he cautioned that there is currently not enough evidence to be sure of this.

Professor Dale Fisher, senior consultant at the National University Hospital's Division of Infectious Diseases, said recent studies had shown reinfections in patients with Omicron are uncommon within the first two months.

But the risk does rise in the case of someone who previously had another strain of the coronavirus and is now exposed to Omicron.

Prof Hsu said that this is because in general, the likelihood of reinfection rises over time, as someone's level of protective antibodies will fall as time passes.

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Newer variants are less vulnerable to the antibodies produced against prior variants, he added.

"The Omicron variant does show some immune escape, whether from vaccines or from prior infection with a different variant," said Prof Fisher.

Professor Paul Tambyah, deputy director of the Infectious Diseases Translational Research Programme at the NUS Yong Loo Lin School of Medicine, said that data from Britain had shown a "small but real" risk of reinfection in a minority of patients.

But he added that the risk is still "very unlikely - about the same likelihood that someone can get chicken pox twice".

Both he and Prof Fisher said it is also unlikely at the moment that someone who had Omicron will get reinfected with another variant.

"Omicron is so transmissible it is the dominant variant globally now, so being infected by another variant is unlikely at the moment. It's also difficult to imagine Omicron being replaced," said Prof Fisher.

But he added that it is possible for Omicron to mutate into another form which evades the immunity provided by today's version of Omicron.

Prof Hsu said: "I have no doubt that people infected with Omicron will eventually be susceptible to infection by newer variants in the future - that is consistent with what we have seen to date, and also with what has been shown for other human coronaviruses."

Prof Tambyah pointed out, however, that because Omicron has evolved to not produce very severe illness in people, it will most likely provide broad protection against other variants, including future even milder and more transmissible ones.

"The milder the virus, the more likely we are to go out and be exposed to multiple individuals who could also infect us with different strains of the virus," said Prof Tambyah.

This exposure will allow people to become immune to the new strains without severe illness. So in such cases, even though Omicron may not necessarily protect against reinfection, it will guard against the severe consequences of Covid-19.

And although Omicron has been able to infect people despite them being vaccinated, the experts all agreed that vaccines continue to be effective against severe disease and death.

"Deaths have probably been reduced eight to tenfold compared with unvaccinated or partially vaccinated persons," said Prof Hsu.

Prof Fisher said: "The most important point is the effectiveness against severe disease. And this fortunately has been a constant so far. If the vaccines and boosters lose their effectiveness against severe disease, we would have a concern, but so far the primary disease and reinfections are mild in the vast majority of those vaccinated."

This article was first published in The Straits Times. Permission required for reproduction.