Drugmakers Pfizer and Moderna are looking to fine-tune their existing coronavirus vaccines against new variants of the virus, with Pfizer studying whether to add another dose.
Pfizer said Thursday it will test a booster shot on an earlier group of volunteers who already received its two-dose vaccine to determine how well it responds to mutated coronavirus strains.
The company, which developed the vaccine with its German partner BioNTech, said it will offer the third dose to 144 participants from its U.S. early-stage testing last year, The Associated Press reported.
Meanwhile, Moderna announced Wednesday that an updated version of its two-dose vaccine has been sent to the National Institutes of Health for a clinical study, CNN reported.
The vaccine was tweaked in response to the B.1.351 variant first seen in South Africa. That variant and several others that have cropped up worldwide in recent weeks are thought to be more contagious than the initial strain, but whether they are more virulent hasn’t yet been determined.
A third vaccine candidate developed by Johnson & Johnson was found this week to be safe and effective by the Food and Drug Administration, which is likely to authorize the company’s one-dose vaccine for emergency use in the coming days.
As of Thursday, the U.S. has administered roughly 66.4 million of its available 88.7 million vaccine doses, according to the Centers for Disease Control and Prevention.