Advisers to the U.S. Food and Drug Administration will vote whether to recommend that COVID-19 vaccines for 2024-25 should target the JN.1 variant, the most dominant this year, documents filed on Monday showed.

Shares of Novavax soared 11% in morning trade, after the documents were released. The company had said last month it would only be able to offer a COVID vaccine in the United States this autumn if regulators accept the shot it started manufacturing to target the JN.1 variant.

The FDA's staff in separate documents said vaccine makers developing the new booster shots may need to consider targeting one of the JN.1 subvariants such as KP.2, as further evolution of the virus could take it away from the older strain.

The documents were posted ahead of the advisers' meeting on Wednesday. The meeting was postponed from May 16 as the FDA sought more time to "obtain surveillance data and other information" on the circulating virus.

The FDA staff's review for updating viral strains for vaccines in the U.S. differs from that of the World Health Organization's advisers, who in April recommended targeting only the JN.1 strain.

Since then, the subvariant KP.2 has become the dominant strain in the U.S., estimated to account for about 28.5% of cases over a two-week period ended May 25, according to data from the U.S. Centers for Disease Control and Prevention.

"This change in epidemiology warrants consideration," the reviewers said.

A variation in vaccine strain from the global norm could also pose a challenge for COVID vaccine makers, especially Novavax as it makes a more traditional protein-based shot that takes longer to manufacture.

Vaccines based on messenger RNA (mRNA), like those from Moderna, or Pfizer and its partner BioNTech , can be developed more quickly. In the past, Pfizer had said it could make the shots in 100 days.