The variant’s swift rise in South Africa hints that it has some capacity to evade immunity. Around one-quarter of South Africans are fully vaccinated, and it’s likely that a large fraction of the population was infected with SARS-CoV-2 in earlier waves, says Wenseleers, based on heightened death rates since the start of the pandemic.in this context, Omicron’s success in southern Africa might be due largely to its capacity to infect people who recovered from COVID-19 caused by Delta and other variants, as well as those who’ve been vaccinated. A 2 December preprint1 from researchers at the NICD found that reinfections in South Africa have increased as Omicron has spread. “Unfortunately, this is the perfect environment for immune-escape variants to develop,” says Althaus.
how well the variant spreads elsewhere might depend on factors such as vaccination and previous infection rates, says Aris Katzourakis, who researches viral evolution at the University of Oxford, UK. “If you throw it into the mix in a highly vaccinated population that has given up on other control measures, it might have the edge there.”
researchers want to measure Omicron’s ability to evade immune responses and the protection they offer. For instance, a team led by Penny Moore, a virologist at the NICD and the University of the Witwatersrand in Johannesburg, is measuring the ability of neutralizing, or virus-blocking, antibodies triggered by previous infection and vaccination to stop Omicron from infecting cells. To test this in the laboratory, her team is making ‘pseudovirus’ particles — an engineered version of HIV that uses SARS-CoV-2’s spike protein to infect cells — that match Omicron, which harbours as many as 32 changes to spike.
another South Africa-based team, led by virologist Alex Sigal at the Africa Health Research Institute in Durban, is conducting similar tests of virus-neutralizing antibodies using infectious SARS-CoV-2 particles. So is a team led by Pei-Yong Shi, a virologist at the University of Texas Medical Branch in Galveston, who is collaborating with the makers of the Pfizer–BioNTech vaccine to determine how it holds up against Omicron. “I was really very concerned when I saw the constellation of mutations in the spike,” he says. “We just have to wait for the results.”
previous studies of Omicron’s spike mutations — particularly in the region that recognizes receptors on human cells — suggest that the variant will blunt the potency of neutralizing antibodies. For instance, in a September 2021 Nature paper2, a team co-led by Paul Bieniasz, a virologist at Rockefeller University in New York City, engineered a highly mutated version of spike — in a virus incapable of causing COVID-19 — that shares numerous mutations with Omicron. The ‘polymutant spike’ proved fully resistant to neutralizing antibodies from most of the people they tested, who had either received two doses of an mRNA vaccine or recovered from COVID-19. With Omicron, “we expect there to be a significant hit”, says Bieniasz.
Will current boosters improve protection against Omicron?
The threat of Omicron has prompted some rich countries, such as the United Kingdom, to accelerate and broaden the roll-out of COVID vaccine booster doses. But it’s not yet clear how effective these doses will be against this variant.
Third doses supercharge neutralizing-antibody levels, and it’s likely that this will provide a bulwark against Omicron’s ability to evade these antibodies, says Bieniasz. His team’s work on the polymutant spike found that people who had recovered from COVID-19 months before receiving their jabs had antibodies capable of blocking the mutant spike. To Bieniasz, those results suggest that people with repeated exposure to SARS-CoV-2’s spike protein, be it through infection or a booster dose, are “quite likely to have neutralizing activity against Omicron”.
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