A major step towards launching a booster campaign to combat the newest members of the omicron family was taken by Pfizer on Monday when they asked US regulators to approve their combination COVID-19 vaccine. The Food and Drug Administration has ordered vaccine makers to modify their shots in order to counter BA.4 and BA.5, which are more effective than ever at suppressing immunity from earlier vaccinations or infections.

Boosters could be available within weeks if the FDA quickly approves the combo shots produced by Pfizer and its partner BioNTech. The U.S. has a contract to buy 105 million of the updated Pfizer doses when health authorities approve them, and the company said the doses are ready for shipment. Other vaccine makers are lagging behind, with Moderna still to file a similar application.