Pfizer and BioNTech said a late-stage trial of their experimental mRNA vaccine to protect against influenza and COVID-19 found the combination shot failed to meet one of the study's two main goals and they are evaluating next steps.

The drugmakers said on Friday the Phase 3 trial showed the vaccine elicited a robust influenza A immune response, compared to a standard flu vaccine, but showed weaker results against the influenza B strain.

The formulation showed similar responses against SARS-CoV-2 as the companies' COVID-19 vaccine.

"We remain optimistic about our combination COVID-19 and influenza program, for which we are evaluating the next steps," Annaliesa Anderson, Pfizer's head of vaccine research and development, said in a statement.

The companies said they are discussing the findings with health authorities and evaluating adjustments to the candidate.

The trial, which compared the experimental vaccine to a licensed influenza vaccine and the companies' COVID-19 vaccine given at the same visit, enrolled 8,000 healthy adults.

The drugmakers said no safety issues with the combination vaccine have been identified.

Pfizer also said a Phase 2 trial of its second-generation mRNA flu vaccine candidate showed that the formulation elicited robust influenza A and B responses, with no safety issues reported.

It said data from the 450-patient flu vaccine trial would be made available at a later date.