There’s a substantial decrease in effectiveness of the Pfizer and AstraZeneca coronavirus vaccines against the Omicron variant, according to a study from researchers at Oxford University.
The results suggest the Omicron variant may drive a new wave of coronavirus infections, the researchers said, although there’s no evidence it would lead to an increase in severe disease or deaths.
“Our findings show that vaccine effectiveness against symptomatic disease with the Omicron variant is significantly lower than with the Delta variant,” the researchers wrote. These findings align with other recently released studies looking at the effectiveness of vaccines against the Omicron variant.
The Oxford researchers used blood samples collected from people who had received two doses of the AstraZeneca or Pfizer Covid-19 vaccines. For the Pfizer vaccine, effectiveness was lower against Omicron than against Delta, except for two to nine weeks after the second dose. Among those who received two doses of the AstraZeneca vaccine, “there was no protective effect of vaccination against symptomatic disease with Omicron from 15 weeks after the second dose.”
These results may be due in part to differences in the populations who received the vaccines. The AstraZeneca vaccine was used early in the UK’s vaccination program, including in nursing homes and among older and higher-risk populations. The Pfizer vaccine’s high level of effectiveness against Omicron at two to nine weeks after the second dose is likely among recently vaccinated young adults and teens.
The study was released as a preprint, which means it has not been peer-reviewed or published.
The researchers noted they could not determine whether vaccines protect against severe disease because of the small number of Omicron cases and the lag between infection and severe illness. “It will be some time before effectiveness against severe disease with Omicron can be estimated but, based on experience with other variants, this is likely to be substantially higher than the estimates against symptomatic disease,” they wrote.
“These data are important but are only one part of the picture,” Matthew Snape, a co-author of the paper and professor in pediatrics and vaccinology at the University of Oxford, said in a statement. “They only look at neutralising antibodies after the second dose, but do not tell us about cellular immunity, and this will also be tested using stored samples once the assays are available.”
“Importantly, we have not yet assessed the impact of a ‘third dose’ booster, which we know significantly increases antibody concentrations, and it is likely that this will lead to improved potency against the Omicron variant.”