Novavax vaccine prevents COVID-19 in studies, but less effective against new variants

Novavax on Thursday said its coronavirus vaccine was nearly 90% effective in preventing symptomatic COVID-19 when compared to a placebo in a large clinical trial in the U.K., a finding that should support clearances for emergency use as the world grapples with new, more infectious variants. 

The Maryland-based drugmaker has already begun the process of seeking authorization for the vaccine in Great Britain, and CEO Stanley Erck said in a call Thursday the company will discuss the same with the U.S. Food and Drug Administration and other regulators. 

A U.S.-based trial that aims to enroll 30,000 volunteers has so far recruited 16,000 people, although some participants who are eligible to receive currently authorized vaccines from Moderna and Pfizer have reportedly begun to drop out of the placebo arm, potentially complicating data collection.

The efficacy estimate announced Thursday was based on an early look at the U.K. trial, which involved some 15,000 people. Investigators recorded 62 cases of COVID-19, 56 of which were in participants given a saline injection. Only six who had received the vaccine got sick with COVID-19. 

Based on the split of cases between groups, Novavax’s vaccine is estimated to be 89.3% effective, close to the roughly 95% efficacy reported for Pfizer’s and Moderna’s shots. 

Volunteers in the Novavax trial were given two doses of vaccine, spaced three weeks apart, and COVID-19 cases were measured beginning seven days after the booster. One severe case was found among those COVID-19 patients, in a volunteer given a placebo. Five of the cases in the vaccine arm were judged to be moderate, compared with 40 in the placebo arm.

For the first time, Novavax provided clinical trial data on vaccine protection against more transmissible coronavirus strains recently observed in several countries around the world. Twenty-eight of the symptomatic cases in the placebo arm had the variant first identified in the U.K., compared with four among patients given a vaccine, suggesting a somewhat lower, but still high efficacy of 86%.

Because Novavax didn’t plan ahead of time to study rates of protection based on coronavirus strains, however, researchers can’t say definitively whether the protection was significantly different.

Novavax also disclosed results from a smaller, Phase 2 trial in South Africa that included data on the distinctive coronavirus variant there, which has mutations that could potentially interfere with immune responses to infection.

Among the 4,400 volunteers in the trial, researchers confirmed 29 cases of COVID-19 in the placebo group, compared to 15 in the vaccine arm, resulting in an efficacy rate of 49%. The rate was slightly higher, 60%, in patients who are HIV-negative. 

The lower effectiveness, albeit from a smaller number of cases, suggest the vaccine’s protection is weaker against the South Africa variant. Researchers were able to sequence viral DNA from 27 of the 44 people who had COVID-19. Of those, 25 were the South Africa variant. 

Still, Novavax is claiming its vaccine is protective against both U.K. and South Africa variants. ”The data have shown profound efficacy against COVID-19 in these trials and with both UK variants and the South Africa escape variants that you’ve been reading a lot about over the last few weeks,” Erck said in the call.

Novavax received $1.6 billion from the U.S. government to support pre-approval manufacturing through the COVID-19 response program formerly called Operation Warp Speed.

Besides the shots from Moderna and Pfizer, U.K.-based AstraZeneca has received authorization in some countries for a vaccine it developed with the University of Oxford, although not in the U.S.

Shares in Novavax rose 21% in post-market trading.