Moderna is asking the US Food and Drug Administration (FDA) to authorize a third booster shot of its COVID-19 vaccine at half of the previously administered dosage.

"Our submission is supported by data generated with the 50 micrograms dose of our COVID-19 vaccine, which shows robust antibody responses against the Delta variant," Moderna CEO Stéphane Bancel said Wednesday.

Moderna will submit the data to the European Medicines Agency (EMA) and other regulatory authorities around the world in the coming days, the company said.

Moderna said its study showed that antibodies had waned significantly after approximately six months following the second shot. A booster dose of 50 micrograms achieved a more robust level of antibody than that observed previously for two doses, Moderna said, and the booster shot significantly increased protection against the current wide-spreading Delta variant by 42-fold.

The company also has completed submission to the FDA for the full licensure of the Moderna COVID-19 vaccine for individuals 18 years of age and older. Pfizer and BioNTech have got such FDA approval over a week ago for their mRNA COVID-19 vaccines.

Some in the government are leaning toward authorizing the 100-microgram dose because of concerns a lower-dose booster might not offer a durable enough boost to counter the fast-spreading Delta variant, The Wall Street Journal reported Thursday. However, one possible benefit of a lower dose is fewer side effects, said the Journal.

Currently, the FDA has recommended a third booster shot of the vaccine for the immunocompromised population only and is still considering the booster shot for the general population.

While a large part of the population is still hesitant to get vaccinated, eager booster seekers are crossing state lines, listing autoimmune disorders they don't have on pharmacy forms and asking healthcare workers to bend rules, the Journal reported.

Those looking to get the additional shots as soon as possible cite factors including the high transmissibility of the Delta variant, the new school year and some employers' return-to-office plan, according to the Journal.

Meanwhile, a new large-scale study showed that fully vaccinated adults are at much lower risk of severe illness and hospitalization, including long-lasting COVID symptoms.

The study, published Wednesday in The Lancet Infectious Diseases journal, used data from more than 1.2 million partially and fully vaccinated adults in the UK from December 2020 to July 2021. Fourteen days or more after the first dose of the Pfizer-BioNTech, Oxford-AstraZeneca or Moderna vaccines, 0.5 percent reported a breakthrough infection. After the second dose, that number dropped to less than 0.2 percent.

"We are at a critical point in the pandemic as we see cases rising worldwide due to the Delta variant,"' study co-lead author Dr Claire Steves said. "Breakthrough infections are expected and don't diminish the fact that these vaccines are doing exactly what they were designed to do — save lives and prevent serious illness."

The odds of experiencing long COVID, or symptoms after 28 days of infection, dropped by 50 percent after two vaccine doses, according to the study.

"Our findings highlight the crucial role vaccines play in larger efforts to prevent COVID-19 infections, which should still include other personal protective measures such as mask-wearing, frequent testing and social distancing," Steves said.