The pharmaceutical giant expressed optimism that its new flu shot would be available this year, after approval concerns.

The federal agency tasked with regulating drugs in the United States has said it will review a flu vaccine application from the pharmaceutical giant Moderna, one week after it declined to do so in an unusual move.

Moderna announced on Wednesday that the Food and Drug Administration (FDA) had accepted a revised application seeking full approval for a new flu shot to be offered to patients between the ages of 50 and 64 and expedited approval for those over 65.

“Pending FDA approval, we look forward to making our flu vaccine available later this year so that America’s seniors have access to a new option to protect themselves against flu,” CEO Stephane Bancel said in a statement.

He also expressed thanks for the FDA’s “engagement” on the issue.

The FDA’s decision to accept Moderna’s application marked an abrupt reversal from its earlier stance. On February 10, Moderna revealed that the FDA had denied its application to review the new flu vaccine for use among older adults.

That announcement sparked concerns in the pharmaceutical industry about how new vaccines would be received under US President Donald Trump, whose administration has rescinded certain vaccine guidelines.

Some Trump officials, most notably Health and Human Services Secretary Robert F Kennedy Jr, have also spread false claims about vaccine safety.

At the time, Moderna called the agency’s rejection “inconsistent with previous written communications” with the FDA.

The decision, Bancel said in a statement, “did not identify any safety or efficacy concerns with our product” and “does not further our shared goal of enhancing America’s leadership in developing innovative medicines”.

The agency’s refusal to consider the company’s application was an unusual move.

In a “refusal to file” letter rejecting the initial application, the FDA’s vaccine director Vinay Prasad argued that Moderna should have included a high-dose brand for comparison in its trial process.

Moderna had undertaken a 40,000-person clinical trial, focused on adults age 50 and older, that concluded its new vaccine was more effective than a standard shot.

The company publicly responded that the FDA had itself recommended that approach when it approved the trial study.

In a compromise, Moderna agreed to conduct another study once the new flu shot is available. The FDA is aiming to reach a decision on the revised application by August 5.

The flu shot was created with mRNA technology, a subject of frequent criticism from Kennedy, who has promoted anti-vaccine views and replaced experts in the Health and Human Services Department with figures who share his scepticism.

Last June, Kennedy cancelled nearly $500m in federal research grants and contracts for research into mRNA vaccines.