After endorsing both Moderna and Johnson & Johnson's COVID booster doses last week, the US Food and Drug Administration is now planning to grant a go-ahead for 'mix-and-match approach for the third jab.

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The FDA is expected to allow the mix-and-match approach by Wednesday evening, which will then be handed to the US Centers for Disease Control and Prevention (CDC) and its vaccine advisory committee, who will make their own decision, New York Times reported.

The CDC's next vaccine advisory meeting is scheduled for October 20-21 where it is expected to discuss the boosters. By the end of the week, more Americans could be eligible for extra shots, the report said.

Last week, FDA's Vaccines and Related Biological Products Advisory Committee conducted a two-day meeting to discuss data on the safety and effectiveness of Moderna and Johnson & Johnson's booster shot in adults and approved them. The US regulators had, earlier this month, authorised COVID booster shots of Pfizer. However, unlike Pfizer, Moderna has been recommended for only a half-dose booster to bolster protection against the virus.

The mix-and-match approach may help those who got the first COVID jab of Johnson & Johnson vaccine and provide flexibility to doctors and other vaccinators, NYT reported. Dr. Anthony Fauci, the government's top infectious disease expert, publicly suggested that the government was headed toward granting greater leeway, at least for Johnson & Johnson recipients. "I believe there's going to be a degree of flexibility of what a person who got the J&J originally can do, either with J&J or with the mix-and-match from other products," he said.

In the two-day meeting, the FDA panel also discussed the results of a preliminary study of a US trial on mixing COVID-19 vaccines as part of a booster programme -- a practice that some experts believe could boost a person's immune response and ease logistical challenges in rolling out boosters.

According to people familiar with the agency's planning, while the government will not recommend one shot over another, vaccine providers could use their discretion to offer a different brand, freedom that state health officials have been requesting for weeks, it added.

A study led by the US National Institutes of Health (NIH) presented to the FDA's advisory panel last week, showed that people who have taken Johnson and Johnson's COVID vaccine will have better results with a booster shot of either Pfizer or Moderna, more than the same vaccine.

Officials have noted that the federal government will cover the cost of a different vaccine as a booster only if the FDA authorises the approach, the report said.