Pfizer and German partner BioNTech said on Thursday that their vaccine to prevent flu and COVID-19 generated a strong immune response against strains of the viruses in an early- to mid-stage trial.

The companies said they plan to start a late-stage trial in the coming months.

"This vaccine has the potential to lessen the impact of two respiratory diseases with a single injection and may simplify immunization practices," Annaliesa Anderson, Pfizer's head of vaccine research and development, said in a statement.

In the trial, the vaccine candidates were compared to a licensed influenza vaccine and the companies' updated COVID-19 vaccine given at the same visit.

The data from the trial showed that the flu-COVID vaccine demonstrated robust immune responses to influenza A, influenza B and SARS-CoV-2 strains, the companies said.