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  • People who have recovered from a coronavirus infection can develop a reinfection with the Omicron variant.
  • Many experts think two doses of a COVID-19 vaccine will protect against severe illness, even against Omicron.
  • Boosters may hold up better than a previous infection or a two-dose vaccine regimen, according to data from Pfizer and BioNTech.

Preliminary results from lab studies were released this week showing that the Omicron coronavirus variant is able to evade some of the protection against infection offered by COVID-19 vaccines.

Boosters, though, may hold up better, according to data from Pfizer and BioNTech. Many experts also think two doses of a vaccine will protect against severe illness, even against Omicron.

“Early information definitely supports that there are enough mutations in the right place in the Omicron variant to escape the maximal benefits of the vaccine,” said Dr. Shira Abeles, an infectious disease specialist at UC San Diego Health.

“But we are optimistic there will be partial protection. So yes, we may be more easily infected, but we remain optimistic that it won’t result in [a large increase in] hospitalizations and deaths.”

But how well will a previous coronavirus infection protect against this new variant?

One study suggests that, in the face of Omicron, people who’ve recovered from a prior infection have a significant risk of reinfection — much higher than with earlier variants.

A preprint study from South Africa found that the risk of reinfection during the recent Omicron wave is substantially higher than the risk seen during the country’s earlier Beta and Delta surges.

Researchers used the country’s extensive records of COVID-19 tests from March 2020 through late November 2021 to estimate the reinfection risk with Omicron.

They found that the risk of infection remained stable during the earlier surges caused by Beta and Delta, but increased dramatically since the arrival of Omicron.

“We find evidence of increased reinfection risk associated with emergence of the Omicron variant, suggesting evasion of immunity from prior infection,” study author Juliet Pulliam, PhD, who directs the South African DSI-NRF Centre for Excellence in Epidemiological Modelling and Analysis at Stellenbosch University, wrote on Twitter.

Recent reinfections occurred in people whose original bout with the virus happened during the previous waves, but mostly from people who had a previous infection during the Delta wave.

The reinfection rates that Pulliam and her colleagues saw in South Africa may not be the same in other countries, which have different levels of COVID-19 vaccination, boosting, and age distributions.

In addition, other factors can affect a person’s risk of reinfection, including personal behaviors, public health measures such as mask mandates, and people’s specific immune profiles.

So it’s difficult to draw too many conclusions from the South Africa data.

In addition, Pulliam and her colleagues didn’t have information about the vaccination status of the people included in their data set, so they can’t tell “whether Omicron also evades vaccine-derived immunity,” Pulliam wrote on Twitter.

But recent preliminary data from Pfizer and BioNTech and other research groups have found a reduction in the level of neutralizing antibodies against Omicron in people who have been vaccinated.

Shelley M. Payne, PhD, a professor of molecular biosciences at the University of Texas at Austin, said these kinds of laboratory studies compare how well antibodies generated in response to the vaccine or prior infection can neutralize the Omicron variant.

“This will give researchers a good idea of what levels of antibodies will prevent the virus from infecting cells,” she said.

A higher level of neutralizing antibodies is better, but it’s not clear yet what level is needed to provide a certain amount of protection.

Or how the level of neutralizing antibodies translates to the real world.

“If there is no neutralization in the laboratory tests, we would expect the variant to cause disease, even in vaccinated individuals,” said Payne. “However, antibody neutralization of the virus in the laboratory doesn’t ensure that disease won’t occur.”

While neutralizing antibodies are a key measure of the immune response to vaccination and prior infection, they are not the only one.

“T cells, the general health of the person or underlying conditions, for example, will also influence whether a person will be infected and, if infected, how severe the disease may be,” said Payne.

Some research also suggests that the variant that people initially contract can shape their immunity in such a way that they have different levels of protection against different variants.

Additional real-world studies are needed to determine the Omicron reinfection risk as well as the risk of severe illness and death.

This includes looking at the risk for different immunity subgroups, such as people who’ve had two doses of a vaccine, two doses plus a booster, prior infection and two doses, or prior infection and three doses.

As Omicron continues to spread, these kinds of studies will be easier to carry out.

“As more people are infected with the Omicron variant, the clinical and epidemiological data will show whether vaccination or previous infection protects against severe illness or hospitalization,” said Payne.

As we wait for the results from additional studies on Omicron, experts say the benefits of the COVID-19 vaccines are clear.

Unvaccinated people are 14 times more likely to die from COVID-19, compared with fully vaccinated individuals, according to data from the Centers for Disease Control and Prevention (CDC).

“As far as people who had COVID prior, they should get vaccinated, and vaccinated persons should get boosted,” said Abeles.