Pfizer's COVID-19 vaccine may yield substantially fewer antibodies against the Omicron variant.
One study found the vaccine showed a 40-fold reduction in antibody levels in a study awaiting peer review.
Breakthrough infections still appear to be mild.
The Omicron variant substantially reduced antibody levels generated by the Pfizer-BioNTech COVID-19 vaccine, according to preliminary results from a South African study that's still awaiting peer review.
These are the first laboratory results to see how a COVID-19 vaccine holds up to Omicron. A team of researchers led by Africa Health Research Institute's Alex Sigal tested 14 blood samples from 12 people against a live sample of the Omicron variant. All 12 people were vaccinated, and six were previously infected.
Overall, the scientists found a roughly 40-fold reduction in the levels of neutralizing antibodies, the virus-fighting proteins that play a key role in our immune response, compared with the original version of the virus.
Omicron did not evade vaccine protection completely, Sigal wrote on Twitter, meaning there's still benefit to being vaccinated against this new variant. But the marked reduction in antibodies raises questions of how durable vaccine protection will be against Omicron - namely, whether booster shots will sufficiently ward off disease or if new vaccines may eventually be required. Sigal called it a "very large drop in neutralization of Omicron."
"A good booster probably would decrease your chance of infection, especially severe infection leading to more severe disease," Sigal said in an online presentation of his results on Tuesday, according to Bloomberg. "People who haven't had a booster should get one, and people who have been previously infected should be vaccinated."
Shortly after Sigal announced his team's results, another group of researchers at Sweden's Karolinska Institutet disclosed their own findings that suggested a substantial but less dramatic decline in antibody levels. The Karolinska team found a seven-fold reduction across 17 blood samples.
They noted the impact of Omicron varied greatly between samples, and they used a version of Omicron that was artificially made in a lab instead of the live virus. A lead researcher for that group said the findings make Omicron "certainly worse than Delta, but, again, not as extreme as we expected."
Other variants have also shown the ability to partially evade the vaccine's protection to a lesser degree. Previous lab tests showed the Delta variant led to a 2- to 3-fold reduction in antibodies compared with the original virus, while the Beta variant caused a 7- to 8-fold reduction.
The results are not finalized and have not been published in a medical journal. Sigal cautioned on Twitter that the findings "are likely to be adjusted as we do more experiments."
Drugmakers are working on variant-specific boosters
Pfizer Chief Scientific Officer Mikael Dolsten previously told Insider he'd be worried to see a 10-fold reduction in antibody levels. A decrease of that magnitude, he said, would make him concerned that current vaccines wouldn't offer sufficient protection and an Omicron-specific shot would be needed.
"If we exceed a 10-fold drop in neutralization of Omicron, I think we are starting to enter the yellow to red zone, when your immunity is likely lowered and there's limited time after your boost until waning," Dolsten said in a November 29 interview.
Several vaccine developers, including Pfizer, Moderna, and Johnson & Johnson, are already working on Omicron-specific shots. Dolsten said an updated version could be ready to start mass-producing as soon as March 2022.
The South African study only analyzed blood samples from people who got two shots of Pfizer's vaccine, not people who'd received a booster shot. Five of the six blood samples that came from people who were both vaccinated and previously infected showed relatively high levels of neutralizing antibodies against Omicron.
"Previous infection, followed by vaccination or booster is likely to increase the neutralization level and likely confer protection from severe disease in Omicron infection," the researchers wrote.
Even reduced antibody levels may still protect against severe disease
It's still unclear if Omicron will impact vaccine protection against severe disease.
Virologists are cautiously optimistic that the vaccines could still help prevent critical illness, despite significant drops in antibody levels. Vaccines also activate other parts of the immune system, particularly B- and T-cells that often confer protection against variants.
Anecdotally, disease experts in South Africa have suggested that vaccines still seem to reduce the risk of serious illness among Omicron cases.
"We are seeing breakthrough infections of people who have been vaccinated, but the infections we're seeing are very mild to moderate," Richard Friedland, chief executive officer of Netcare, which operates South Africa's largest private healthcare network, told Bloomberg on Friday. He added that "for healthcare workers who have had boosters, it's mostly mild."
But Omicron has also shown signs of being highly transmissible compared with other coronavirus strains. The variant has spread to more than 40 countries since it was first detected roughly a month ago.