Moderna filed an application with the U.S. Food and Drug Administration (FDA) on Thursday to authorize a fourth dose of the vaccine for all adults, a broader application than the Pfizer/BNT filing. Anthony Fauci, the top White House anti-epidemic expert, is worried that confirmed cases in the United States may rise again in the short term like the United Kingdom, and high-risk groups may need a fourth dose.

While the debate over the vaccine’s protection and the need for a fourth dose is inconclusive, a handful of countries, such as Israel, have begun vaccinating adults with a fourth dose of the Covid-19 vaccine.

Moderna’s (MRNA-US) FDA-approved fourth dose is intended for all adults, with the hope that a medical practitioner will assess on an individual basis who could benefit from it. The company said that the application was based on data released by the United States and Israel after the Omicron variant appeared.

Pfizer (PFE-US) recently applied for a fourth dose for high-risk seniors over the age of 65, mainly based on Israeli research data.

On the other hand, Fauci said on Thursday that judging from the trajectory of the British epidemic, the United States may soon see an increase in the number of confirmed cases, and high-risk groups may need a fourth dose of the vaccine.

The Covid-19 outbreak in the U.K. typically develops weeks earlier than in the U.S., and U.K. officials have warned Fauci that Omicron BA.2 has led to an increase in the number of confirmed cases in the U.K., easing travel restrictions and declining vaccine protection are also possible factors.

“We have all three factors,” Fauci said. “I’m predicting a slight increase in the number of cases, or at least a flattening of the decline curve. The question is how do we respond.”

The White House warned on Tuesday that the U.S. could be forced to stop supplying more boosters and monoclonal antibody drugs as soon as May as Congress refrains from pumping more money. The White House has asked Congress to immediately provide $22.5 billion in emergency funding to fight the outbreak.