LONDON - The European Medicines Agency (EMA) is open to using next generation COVID-19 vaccines that target older offshoots of the Omicron variant this fall, an official said on Thursday, amid a rise in cases due to new Omicron subvariants.

While the existing coronavirus vaccines continue to provide good protection against hospitalisation and death, vaccine effectiveness has taken a hit as the virus has evolved. The EMA expects new COVID vaccine boosters to be approved by September.

Vaccines designed to target the newer BA.4 and BA.5 strains of Omicron, currently driving a surge in new infections globally, have only recently entered clinical development, so how quickly any such vaccine could be made available is also a consideration, said Marco Cavaleri, EMA's head of health threats and vaccines strategy.

"That's why for the time being we still think that it's very good to keep all options open and to not exclude any of these candidates from any potential approval," he told a press briefing.

In contrast to the EMA position, the U.S. Food and Drug Administration (FDA) has said that it would seek the inclusion specifically of the newer BA.4 and BA.5 strains of Omicron in any new shots used domestically.

"The problem is that nobody can predict what will be circulating in the fall and maybe BA.5 is not circulating anymore, then what are we going to do?," the EMA's Cavaleri added on Thursday.

"We should be extremely careful in not thinking about chasing the virus continuously and thinking that we can be ready with a vaccine composition that is exactly matching what will be in circulation in the future. That is simply impossible."

Vaccine makers, such as Moderna Inc and partners Pfizer Inc and BioNTech SE have been testing versions of their vaccines modified to combat the BA.1 Omicron variant.

Although they have said those vaccines generated a good immune response against BA.1 and the more recently circulating variants, they did see a lower response against BA.4 and BA.5.

Vaccine makers have indicated they could run two production lines for the adapted vaccines in case of differing regulatory requirements in Europe and the United States, EMA officials noted on Thursday.

Both the U.S. FDA and EMA have said recently they would also consider new booster shots based on non-Omicron variants such as Beta.

Sanofi SA and partner GSK Plc are working on protein-based vaccines that targets the Beta subvariant, which dominated for some time last year.

(Reporting by Natalie Grover in London and Ludwig Burger in Frankfurt Editing by Toby Chopra, Frances Kerry and Jonathan Oatis)