President Biden’s chief medical adviser Anthony Fauci said in an interview that it is not clear yet if people will need yearly COVID-19 boosters, even as the chief executives of several drugmakers have indicated a fourth vaccine dose may be necessary.

“We’ve only recently boosted people. We will find out if the booster gives you a degree of durability of protection and actually should be the standard regimen of three doses of an mRNA and two doses of J&J,” Fauci said in an interview with NBC News published on Thursday.

“Or — and it’s a big ‘or’ right now — will we need to boost people every year or so?” he continued.

Fauci said that he while it was a good thing that the original ancestral strain of COVID-19 was used in the development of the COVID-19 vaccine — because “we were fortunate that even though [strains] were different, they were not so different that the vaccine didn’t cover it well” — omicron has muddled the situation.

“We were doing quite well with a primary vaccination and a boost with delta. Then all of a sudden omicron came along,” Fauci told the network. “And if you look at the efficacy against the delta versus omicron, it went down to around 30 percent.”

The leading infectious diseases expert said that he wants a vaccine that would ideally be effective against all kinds of COVID-19 variants.