Omicron is able to evade immunity significantly better than any other version of the coronavirus seen so far, according to the first laboratory experiments into the variant.
However, the research from South Africa also found that there were signs that those who had had boosters would still have reasonable protection.
Tests on the blood of people who were fully vaccinated showed that their antibodies were one-fortieth as capable of latching on to Omicron and preventing infection compared with the original strain.
Researchers cautioned that these laboratory findings did not translate precisely into real-world vaccine efficacy, and also that the experiments did not look at other immune responses that would be likely to protect against severe disease. This “robust, but not complete” immune evasion nevertheless showed the variant had “much more extensive escape” than previous variants, said Dr Alex Sigal, from the Africa Health Research Institute.
The “very large drop in neutralisation of Omicron”, he added, strongly suggested that it would be better at infecting people who were vaccinated.
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The work involved tests against blood sera taken from 12 people. Half had just been double vaccinated while half had also had an infection. In those with prior infection, there was still a significant drop in the ability of antibodies to neutralise the virus but from a high enough level that protection remained.
Sigal said that this was good news. “Previous infection, followed by vaccination or booster is likely to increase the neutralisation level and likely confer protection from severe disease in Omicron infection,” he wrote, in a preprint published before peer review.
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Work at Karolinska Institute in Sweden, which used “pseudoviruses” containing many of the relevant mutations, yesterday found a less severe but significant seven-fold drop in neutralisation.
The findings help to explain preliminary real-world studies in South Africa that found the variant appeared to be about two and a half times more likely to cause reinfections.
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Some immunologists had feared that the changes to the spike protein of the variant were so significant that it would evade immunity entirely or have a different mode of action. One of the tests in the experiment was to check that the virus still used the same entry point to cells, a route known as the ACE2 receptor. “This was better than I expected of Omicron,” Sigal said. “The fact that it still needs the ACE2 receptor and that escape is incomplete means it’s a tractable problem with the tools we’ve got.”
In the coming weeks epidemiologists will get a better understanding of how the mutations in the variant translate into real-world outcomes, and especially into disease severity. There have been very early suggestions from South African hospitals that it may not be causing as bad outcomes in patients.
Daniel Davis, professor of immunology at the University of Manchester, said that these larger-scale studies would be key, and that laboratory evidence would only show a certain amount. “This is an important study — but more ‘real-world’ data is still sorely needed,” Davis, author of The Secret Body, said. “Crucially, it’s hard to translate these lab tests into knowing what actually happens overall in people infected with Omicron, after vaccination or a real infection. The virus has complex effects on the body and immune response is multifaceted. So, what happens in people is the data we need and should be available soon. In the meantime, the evidence here is that Omicron can avoid immunity to some extent and it’s a vital judgement that society has to make about if and when we need to act.”
