(Reuters) -Shares of global vaccine makers were mixed on Tuesday, as investors assessed U.S. Health Secretary Robert F. Kennedy Jr.'s surprising decision to fire all 17 members of a key expert panel late on Monday.

Shares of U.S. vaccine maker Moderna ( MRNA ) fell 2%, while Novavax ( NVAX ) was down marginally. Merck ( MRK ) and Pfizer ( PFE ) rose between 1.4% and 2%. Shares of AstraZeneca ( AZN ) closed slightly higher, while BioNTech closed marginally lower.

Analysts and investors said that while the unprecedented dismissals of all members of the Advisory Committee on Immunization Practices (ACIP) represented a risk for vaccine makers, the weak performance of those stocks in 2025 suggested that Kennedy's skepticism around vaccines was already factored in.

Shares of most big drugmakers are down in 2025, compared with a 2% gain in the S&P 500 index.

Since his appointment as health secretary under President Donald Trump, Kennedy has made several changes to reshape the regulation of vaccines, food and medicine. However, firing members of the ACIP remains his most far-reaching move yet. 

"For vaccine makers, policy risk has already been cemented into share prices," Morningstar analyst Karen Anderson said, even though the move was sudden and went against the promises that Kennedy made to Senator Bill Cassidy before his appointment was confirmed.

Kennedy's decision comes less than three weeks before the next panel meeting, where the committee is slated to discuss recommendations for who should receive vaccines for diseases like respiratory syncytial virus, or RSV.

"It seems difficult to refill the panel with experts before the June 25th meeting," said Jeff Jonas, portfolio manager at Gabelli Funds.

"But it's clearly going to be more difficult and more expensive to get future vaccines approved, and I'd expect to see less industry focus and effort here," Jonas added, despite recent positive news such as the limited approval of Novavax's ( NVAX ) COVID shot and Merck's ( MRK ) RSV therapy.

Some analysts expressed concerns that the new committee members, who have not been named, might be more sympathetic to Kennedy's views on vaccines, an idea shared by scientific experts and doctors.

Although the makeup of a reconstituted ACIP is yet to be determined, "new members will likely be sympathetic to at least some of RFK's beliefs regarding alleged dangers of vaccines," Leerink analyst Daina Graybosch wrote in a note. 

Graybosch said that the move could negatively impact approved vaccine recommendations and increase the burden of evidence and costs for future vaccine development.

It is unclear when Kennedy will announce the new members, who the agency said are under consideration, or whether the agenda will follow the meeting description posted on the Federal Register on Monday.

(Reporting by Joel Jose, Bhanvi Satija and Sriparna Roy in Bengaluru; Editing by Anil D'Silva)