WASHINGTON — A Food and Drug Administration vaccine advisory committee meeting that was set to discuss what flu strains to include in next season's flu vaccine has been canceled, multiple sources told ABC News, leaving some to wonder if the meeting cancelation will delay next year's flu vaccine delivery schedule.

The meeting was canceled in an email sent from the FDA to members who were planning to attend the annual meeting in about two weeks.

The high-profile, public meetings of the Vaccines and Related Biological Products Advisory Committee are where independent experts review scientific data and vote on a variety of vaccine related issues. Members of the March 13 meeting were set to vote on which flu strains would offer the most protection in next season's flu shot.

"Influenza vaccines aren't perfect and to get the best influence vaccine each year requires predicting the strain as best we can," said Dr. Andrew Pavia, professor of pediatrics and medicine at the University of Utah and a spokesperson for the Infectious Diseases Society of America. "There's a lot of complex data that needs to be reviewed and having a number of experts do it gives us the best chance of making the best prediction."

The meeting typically takes into consideration recommendations from WHO. It also receives input and data from the Centers for Disease Control and Prevention, the Department of Defense and vaccine manufacturers.

The timing of this meeting aligns with the six-month lead time typically required for vaccine manufacturing to ensure vaccines are ready for distribution in the fall -- before peak flu season hits in the United States.

"I can't think of any rational reason to do this other than to throw a hand grenade into vaccine production," Pavia said. "The impact is going to be felt in terms of our ability to reduce flu hospitalizations and flu deaths."

Earlier in the week, officials and specialists at the CDC virtually joined the annual WHO meeting to discuss the upcoming flu vaccine strain for next year, despite being previously ordered to halt all communication with the global health organization.

Typically, the Vaccines and Related Biological Products Advisory Committee meets after the WHO meeting to finalize recommendations.

It remains unclear what impact the meeting cancellation may have on next season's flu vaccine. But experts are concerned about the timing because flu vaccines are made using chicken eggs to grow and harvest the virus before processing it into a vaccine.

"It's a very very tight timeline because it takes a long time to create the template viruses and then grow them in eggs," Pavia said. "It is a many months long process and any delay means it will be difficult to have vaccine in time for the next season."

U.S. vaccine strains are usually picked by April. Manufacturing is completed over the summer and delivered for vaccination starting in September.

Sanofi, one manufacturer of flu vaccines, told ABC News the company has already started the initial steps of manufacturing.

"Just as every year, we have already begun production for the 2025-2026 flu season in the Northern Hemisphere and will be ready to support final strain selections in time for the season," a spokesperson for Sanofi told ABC News.

However, the FDA must approve the final strains for the shots to be legally marketed and distributed in the U.S.

ABC News has reached out to both the FDA and Health and Human Services for comment.

Dr. Paul Offit, a member of the FDA's independent committee who was planning on attending the meeting said, "Who canceled this meeting? Why did they cancel it? Will the vaccine makers turn to the World Health Organization to determine which strains to include in this year's vaccine?"

"It's very concerning with regard to the ability to produce enough vaccine in time for next year's flu season," Pavia added. "Hopefully, there will be workarounds that could be developed. But what they are -- we don't know yet."

Copyright © 2025, ABC Audio. All rights reserved.