One Vaccine Dose May Not Protect Against Delta—'at All'

A single dose of the two-dose Pfizer or AstraZeneca vaccines is "poorly or not at all efficient" against the fast-spreading Delta variant, say French researchers in a peer-reviewed study published Thursday. The study identified mutations with the Delta and Beta variants of COVID that allow them to evade antibodies produced as a result of vaccines and even a prior infection, reports the Washington Post. Just 10% of participants who'd received one dose of the Pfizer or AstraZeneca vaccines neutralized the variants, per the New York Times. The "good news," according to lead author Olivier Schwartz of Paris' Pasteur Institute, is that figure climbed to 95% with a second dose. Another study by US scientists, published Wednesday, came to a similar conclusion, notes the Post.

“Please, get vaccinated," said Dr. Anthony Fauci on Thursday. "It will protect you against the surging of the Delta variant." This and similar research likely explains why the UK has seen a spike in recent cases, as it opted to delay second vaccine doses in a push to have more people receive an initial dose, says Monica Gandhi, an infectious diseases expert at the University of California at San Francisco. The more transmissible Delta variant was responsible for 51.7% of new infections in the US as of July 3, which is up five-fold in prevalence from a month ago. Some 48% of Americans are fully vaccinated, while 55% have at least one dose. (More COVID variants stories.)