Vaccine makers are looking into whether booster doses could provide better protection against coronavirus variants, Andy Slavitt, the White House’s senior adviser for Covid response, said during an interview with the Washington Post on Thursday.

The White House official said Johnson & Johnson is already studying a second dose of its Covid-19 vaccine, and he noted that Moderna and Pfizer/BioNTech, which currently have vaccines authorized in the United States, “have plans to continue to update their vaccines and if need be, create boosters down the road if there continue to be additional mutants, as there likely will be.”

Johnson & Johnson has said it’s exploring whether to retool its Covid-19 vaccine to address the potential impact of new strains. In November, the company announced that it had started a large-scale Phase 3 trial for a two-dose regimen of its coronavirus vaccine.

“If you have the Johnson and Johnson vaccine, could you later have another vaccine?” Slavitt said. “And I will give you two parts to that answer quickly. One is: Johnson and Johnson, people may know, is currently evaluating whether — how their vaccine performs with two doses — in other words, with their own booster. So, pending the results on that, pending what the FDA has to say if the vaccine’s approved in the first place, there will be — there may be a second shot of Johnson and Johnson.”

“More broadly, can you mix and match? If you have one can you later take another? And the answer is, try to remember which one you had because that’s what’s been tested … but if you forgot, don’t panic. You can take another one and the CDC says that that’s fine in that case,” he continued.

A US Food and Drug Administration’s independent advisory committee will meet Feb. 26 to consider whether to recommend a single dose of the Johnson & Johnson vaccine for emergency use authorization.

The Johnson & Johnson’s Covid-19 single-shot vaccine was shown to be 66% effective in preventing moderate and severe disease in a global Phase 3 trial, but 85% effective against severe disease, the company previously announced.

“While a potentially safe and effective single-dose preventive COVID-19 vaccine would have significant benefits, particularly in a pandemic setting, Janssen’s COVID-19 vaccine program has been designed to be extremely thorough and driven by science. As such, we are investigating multiple doses and dosing regimens to evaluate their long-term efficacy,” a November statement from J&J said. 

Slavitt also said that the administration is working to ensure that the vaccines will work against variants. 

“We are testing right now in vitro. … The good news to start with is the most prominent strain that’s come here, the B.1.1.7, the vaccines work well for — the Pfizer and the Moderna. The South African, which is close to the Brazilian … they are … less effective, but above a threshold,” Slavitt said.