Johnson & Johnson asked US drug regulators to clear its experimental Covid-19 vaccine for emergency use, setting up what is likely to be a fast-moving review process that could lead to millions more doses becoming available to step up a stumbling immunisation drive. The drugmaker said on Thursday that it had filed an application for emergency-use authorisation with the US Food and Drug Administration (FDA). If cleared, the shot would give the US a third vaccine to try to halt a pandemic that has killed more than 450,000 people in the country. The process is likely to take weeks. Paul Stoffels, the company's chief scientific officer, said that the company would be ready to begin shipping vaccines upon receiving authorisation. "With our submission to the FDA and our ongoing reviews with other health authorities around the world, we are working with great urgency to make our investigational vaccine available to the public as quickly as possible," Mr Stoffels said. Shares of the company gained 1.5 per cent in after-hours trading in New York. Over the past 12 months, the stock has advanced 6.85 per cent. Vaccines from Moderna and partners Pfizer and BioNTech SE have already been given similar clearance and are the only two vaccines available to most Americans. The Moderna and Pfizer-BioNTech vaccines, which in clinical studies were each found to be more than 90 per cent effective, should be given in two doses spaced several weeks apart, according to their authorisations. Johnson & Johnson's vaccine <a href="https://www.thenationalnews.com/world/europe/johnson-johnson-single-dose-vaccine-is-effective-against-covid-19-1.1156096">was found to be 72 per cent effective</a> in preventing moderate to severe Covid-19 after a single shot, and 66 per cent effective overall in a global trial. It was 100 per cent effective in preventing hospital admission and death. Officials at the agency will now review the company’s trial data. The agency is also expected to convene a committee of outside experts to evaluate the trial findings. The panel will then make a recommendation on whether the shot should be allowed on to the US market. The group’s findings are not binding on leadership, but it is unusual for the agency to reject their advice. One question likely to be in focus as experts consider the vaccine’s potential authorisation is its effectiveness against new variants of the coronavirus. While Johnson & Johnson’s shot was 85 per cent effective across the board in preventing severe disease, there were indications it could be less potent against new viral mutations that have caused infections to rise in some countries. In South Africa, where a variant called B.1.351 is circulating widely, the vaccine was only 57 per cent effective. And the shot was 66 per cent effective in Latin America, where another mutation caused cases to climb in Brazil. Both recently surfaced in the US, although there is not yet a clear indication that any are widespread. The FDA said on Thursday that it has been communicating with drugmakers and developing guidelines for vaccine developers as they evaluate how their products will be affected by variants. The agency is “currently deliberating and discussing the types of data needed to support changes in the composition of the vaccine”, said acting agency commissioner Janet Woodcock. US officials last week emphasised the shot's proficiency at preventing the worst forms of Covid-19. “If you can prevent severe disease in a high percentage of individuals, that will alleviate so much of the stress and human suffering” of the pandemic, said Dr Anthony Fauci, the top US infectious disease official. Johnson &Johnson previously indicated that it expected an emergency clearance as soon as March and that it would have millions of doses ready to ship upon receiving a nod from regulators. It vowed to deliver 100 million doses to the US by the end of June and maintains that it will be able to meet all other supply commitments.