It didn’t take long before a morale boost for AstraZeneca’s COVID-19 vaccine was overshadowed by disappointment over its waned protection against a newly emerged coronavirus variant.
A new study has found AZ’s COVID-19 shot offered “minimal protection” against mild to moderate disease caused by the B.1.351 variant, which was first identified in South Africa, the University of Oxford, the original developer of the vaccine, said Sunday.
The finding has prompted the pair to update their vaccine, dubbed AZD1222, to target variants of the coronavirus with mutations similar to B.1.351. In the meantime, South African authorities have halted rollout of the vaccine as they try to figure out the best way forward.
“Efforts are underway to develop a new generation of vaccines that will allow protection to be redirected to emerging variants as booster jabs, if it turns out that it is necessary to do so,” Sarah Gilbert, Ph.D., of the University of Oxford said in a statement. A modified version could be ready by fall, she said, according to the BBC.
The bad news came on the heels of another Oxford study showing AZD1222, also known as ChAdOx1 nCoV-19, remains effective against the B.1.1.7 variant, which was first spotted in the U.K. Both B.1.1.7 and B.1.351 are more contagious than the original SARS-CoV-2 virus, but it appears that B.1.351 is the tougher one to tackle for existing vaccines and antibody drugs.
In the current study, scientists analyzed data from 2,000 volunteers who got the AZ shot in a phase 1/2 clinical trial in South Africa. They found the vaccine was only 22% effective at protecting against mild to moderate COVID-19, according to multiple media reports. The vaccine’s neutralization titers against B.1.351 were “substantially reduced” when compared with those for the original version of the virus, according to Oxford. The full data haven’t been released.
Because the trial participants are mainly young and fit adults who were on average 31 years old, the study wasn’t able to assess protection against moderate to severe disease, hospitalization or death.
In a statement, an AstraZeneca spokesperson said the company believes AZD1222 can protect against severe disease caused by B.1.351, “as neutralizing antibody activity is equivalent to that seen with other COVID-19 vaccines that have demonstrated activity against more severe disease.” The spokesperson pointed out that no severe disease or hospitalization was recorded in the early-phase trial.
AZD1222 isn’t the only COVID-19 vaccine to have lost some of its power against the B.1.351 variant. Previously, Moderna reported a sixfold reduction in neutralizing titers for mRNA-1273 against B.1.351. While the Massachusetts biotech maintained that the shot was still able to protect people, it has started making a booster shot targeting the variant.
As is the case with AZD1222, Johnson & Johnson’s COVID-19 vaccine candidate also wraps a piece of the coronavirus’s DNA in an adenovirus vector. In its phase 3 trial, the J&J shot was found to be 72% effective at fending off moderate to severe disease in the U.S., whereas its protection fell to 57% in South Africa, where the B.1.351 variant is prevalent.
Novavax’s adjuvanted candidate NVX-CoV2373 also showed weaker efficacy in South Africa. In its phase 3 trial in the U.K., the protein-based vaccine demonstrated an efficacy of 89.3%. But in a phase 2b trial in South Africa, the number dropped to 60%, with 90% of confirmed infections attributed to B.1.351.
Amid rising concerns over new virus variants that could be resistant to existing vaccines, several companies have started to design booster shots. Besides Moderna and AZ, Pfizer and partner BioNTech are also working on an updated version of its mRNA vaccine Comirnaty, and CureVac has teamed with GlaxoSmithKline—with help from the U.K. government—to develop multivalent vaccines or potential booster shots to CureVac’s phase 3 candidate.