New studies indicate mRNA vaccines provide limited protection against Omicron, but boosters and new shots may be crucial
The first substantial evidence for how mRNA vaccines will hold up against the new Omicron variant was released Tuesday night from scientists in South Africa.
The study, conducted by mixing sera from vaccinated individuals with live Omicron virus, showed that the variant could largely — but not entirely — dodge antibodies elicited by the Pfizer-BioNTech vaccine.
The result suggests that the vaccines will be less effective at preventing infection by Omicron. But because many antibodies do still bind to the virus, experts say, boosters should help stem the decline. And efficacy will likely hold up against the most important metric for vaccines: preventing severe disease.
On Wednesday morning, Pfizer added its own early data from internal studies, echoing the results from South Africa while providing evidence that boosters can improve efficacy.
“The important question is whether vaccines will maintain efficacy against severe disease, meaning disease that will cause you go to the doctor or a hospital” Paul Offit, director of the Vaccine Education Center at Children’s Hospital of Philadelphia, told Endpoints News. “And I think the answer to that is in all likelihood yes.”
Florian Krammer, a vaccinologist at Mt. Sinai School of Medicine, chimed in on Twitter, saying “Protection against severe disease may remain reasonably high in all individuals with baseline immunity,” though he cautioned it “was speculation.”
4)….will take a hit and will be strongly reduced. I think protection against infection will remain higher in convalescent vaccinated and 3x vaccinate individuals. I would also speculate, that protection against severe disease may remain reasonably high in all…
— Florian Krammer (@florian_krammer) December 8, 2021
Caveats about the early data abound. The study, led by Alex Sigal, a virologist at the Africa Health Research Institute in Durban, South Africa, only looked at the efficacy of antibodies from six people who had received two doses of the Pfizer shot. They found a 41-fold reduction in neutralization compared to previous versions of the virus.
In people who have received three doses, the quantity of the antibodies may compensate for some of the reduced quality. Indeed, Pfizer said its own data confirmed reduced efficacy for those who received two doses. But the company noted it found sera from individuals who received boosters one month prior can still neutralize the virus.
It remains unclear, though, how long that increased protection lasts, Walid Gellad, director of the University of Pittsburgh Center for Pharmaceutical Policy and Prescribing, said on Twitter. Antibody levels tend to climb substantially after every dose but then fall off.
New data from Pfizer.
We need to know how this differs by age, and by prior infection status. These data are 1 month after booster – what about 4 months after booster? How many times should we boost to increase neutralization if protection against severe disease is maintained? https://t.co/0rpuetXYCt
— Walid Gellad, MD MPH (@walidgellad) December 8, 2021
Antibodies are only one part of a complex and multi-pronged immune response. They are particularly affected by the new variant and its 30 spike protein mutations because to be effective, they need to latch onto the spike, at which point they either block its function or recruit other immune cells to gobble the virus.
T cells, though, don’t need to bind to the spike. They seek out infected cells, inducing any they recognize to self-destruct. Researchers expect these will remain effective against the variant, helping protect vaccinated individuals from severe disease.
In its statement, Pfizer said that 80% of spike epitopes — regions, basically — recognized by killer T cells are not affected by Omicron’s mutations. Offit noted these cells have maintained efficacy against every variant throughout the pandemic.
Nevertheless, these data suggest that Moderna and Pfizer should continue developing an Omicron-specific jab, Fred Hutch virologist Jesse Bloom told The New York Times.
“Given the very large drop in neutralizing antibody titers that are seen here with Omicron,” he said, “certainly in my view it would merit pushing forward as fast as possible with making Omicron-specific vaccines, as long as it seems like there’s a possibility it could spread widely.”
Pfizer, in its statement, indicated they were still evaluating whether such a shot would be necessary. But they are working on new sequences and, if needed, those will be ready for trials by March.
The question, Offit said, centers around precisely what the goal of new shots is. Officials can keep rolling out boosters, against the original virus or against the Omicron variant, to try and stop infection or mild disease. But he noted officials historically haven’t asked that of vaccines against flu, rotavirus or most other bugs, and he questioned how much of an impact such boosters, particularly for young people, would make on the course of the pandemic.
Variant-specific boosters will be needed in the unlikely event Omicron can still cause severe disease in vaccinated individuals, he said. Researchers should have more data on that soon.
“I think we should know that within weeks,” he said. “If Omicron is as contagious as is claimed, there are a lot of people out there who have been vaccinated who are going to be infected with this virus.”
How those patients fare could give researchers the best glimpse yet as to how much a threat Omicron is vaccinated. In the meantime, Offit said, the biggest need is to get more people — including kids — vaccinated for the first time.