Japan's health ministry Thursday gave fast-track approval to use U.S. biotechnology firm Moderna Inc.'s COVID-19 vaccine as booster shots as the country steps up efforts to keep new coronavirus infections at bay.

The approval came after the ministry gave the green light last month to use Pfizer Inc.'s COVID-19 vaccine as booster shots.

Health minister Shigeyuki Goto said before parliament that the rollout of booster shots using Moderna's vaccine is expected to start as early as next month.

The ministry decided to provide Moderna's booster shots for free at least six months after an individual aged 18 or older has received their second dose.

Japan has set an eight-month interval "in principle" between the second shot and a booster but has been working to bring forward the timing of the third shot following the emergence of the Omicron variant of the virus.

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The third dose will use half the 0.5 milliliter amount used for each of the first two shots.

In clinical trials, Moderna administered 0.25 milliliters for a third dose after a period of more than six months had elapsed since the second shot was administered and found that half of the amount is effective against COVID-19.

As for adverse reactions after receiving a booster dose, a clinical study has found that 83.8 percent of people complained of pain at the injection site and 55.1 percent headache. The percentages were about the same as those seen after the second dose was administered.

With the use of Moderna's vaccine, a few severe reactions, including myocarditis and pericarditis, have been reported among young men, and the ministry has said it will continue to warn about those potential side effects.

Meanwhile, Anthony Fauci, director of the U.S. National Institute of Allergy and Infectious Diseases, said Wednesday that although the two doses of Moderna's vaccine are less effective against Omicron, tests have shown that its booster shot significantly increases neutralizing activity against the variant.

"Our booster vaccine regimens work against Omicron. At this point, there is no need for a variant-specific booster," Anthony Fauci said in a press briefing at the White House.

With Japan planning to begin administering third shots for the elderly in January, following the start of the booster program for health care workers earlier this month, Takeda Pharmaceutical Co. submitted Thursday a new drug application for Novavax Inc.'s vaccine to the health ministry.

Takeda will handle distribution of the U.S. biotechnology firm's TAK-019, the first protein-based COVID-19 vaccine candidate for the application, in Japan.

The vaccine demonstrated a robust immune response and was well-tolerated with no serious adverse events after 0.5 milliliter was administered twice on healthy Japanese adults 21 days apart during a domestic clinical trial, according to an interim report analysis from Takeda.

The two companies are working to establish the capability to manufacture the vaccine at Takeda's facilities in Japan with an aim to start distribution in early 2022, if approved.

The health ministry has signed a deal to receive 150 million doses of the Novavax vaccine from as early as the beginning of 2022.