Citing the Delta Variant, Pfizer Will Pursue Booster Shots and a New Vaccine

Scientists were critical of the announcement, pointing to evidence that the current two-dose regimen is powerfully effective against the coronavirus.

Pfizer and BioNTech announced on Thursday that they were developing a version of the coronavirus vaccine that targets Delta, a highly contagious variant that has spread to nearly 100 countries. The companies expect to begin clinical trials of the vaccine in August. Pfizer and BioNTech also reported promising results from studies of people who received a third dose of the original vaccine. A booster given six months after the second dose of the vaccine increases the potency of antibodies against the original virus and the Beta variant by five- to tenfold, the companies said. Vaccine efficacy may decline six months after immunization, the companies said in a news release, and booster doses may be needed to fend off virus variants.