Recipients of the one-shot Johnson & Johnson COVID-19 vaccine may need to get a second dose to protect against the Delta and Lambda coronavirus variants because its less effective against them, a new study suggests, per The New York Times

“The message that we wanted to give was not that people shouldn’t get the J&J vaccine, but we hope that in the future, it will be boosted with either one dose of J&J or a booster with [the Pfizer and Moderna COVID-19 vaccines],” Nathaniel Landau, a virologist at New York University’s Grossman School of Medicine who led the study, told the Times.

The study, which has not been peer reviewed, involvded Landau and his team looking at blood samples taken from 17 people who had received both doses of the Pfizer and Moderna vaccines and 10 people with one dose of J&J. The J&J vaccine started out with a lower efficacy rate, which dropped more sharply against the variants, the Times reports. However, because the study was based on lab experiements, the Food and Drug Administration is unlikely to change its single-dose recommendation because of it, the Times notes. Further, seperate small studies published by researchers affialiated with J&J found that the vaccine’s protection strengthened over time. Read more at The New York Times.