WASHINGTON: The United States on Saturday (Feb 27) authorised Johnson & Johnson's COVID-19 vaccine for emergency use, giving the nation a third shot to battle the outbreak that has killed more than 500,000 Americans.
The single-shot vaccine is highly effective in preventing severe COVID-19, including against newer variants, the Food and Drug Administration (FDA) said before approving it.
"The authorisation of this vaccine expands the availability of vaccines, the best medical prevention method for COVID-19, to help us in the fight against this pandemic," said the US regulator's acting director Janet Woodcock.
The FDA announced the emergency use authorisation for adults aged 18 and older following Friday's unanimous endorsement by the agency's panel of outside experts.
In large clinical trials, the vaccine's efficacy against severe disease was 85.9 per cent in the United States, 81.7 per cent in South Africa, and 87.6 per cent in Brazil.
Overall, among 39,321 participants across all regions, the efficacy against severe COVID-19 was 85.4 per cent, but it fell to 66.1 per cent when including moderate forms of the disease.
Crucially, analyses of various demographic groups revealed no marked differences across age, race or people with underlying conditions.
US President Joe Biden hailed the "exciting" announcement but warned the nation could not let its guard down.
"This is exciting news for all Americans, and an encouraging development in our efforts to bring an end to the crisis," Biden said in a statement after the J&J vaccine got the green light.
"But we cannot let our guard down now or assume that victory is inevitable."
HOW DOES IT DIFFER FROM THE PFIZER AND MODERNA VACCINES?
The Pfizer-BioNTech and Moderna vaccines use new messenger RNA technology to create an immune response and both require two shots. The J&J vaccine involves a more conventional approach, using a common cold virus to introduce coronavirus proteins into cells to trigger an immune response.
The vaccine remains stable for at least three months at normal refrigerator temperatures, while the Moderna vaccine must be shipped frozen and the Pfizer-BioNTech option must be shipped and stored at even colder sub-Arctic temperatures.
These factors make it easier to vaccinate larger numbers of people, even in areas with poor transportation and storage infrastructure.
Pfizer-BioNTech and Moderna vaccines were about 94 per cent to 95 per cent effective in trials conducted in the United States where variants were not circulating.
READ: US$1.9 trillion COVID-19 plan clears US House, heads to Senate
Both mRNA vaccines showed higher efficacy rates in their trials than J&J's vaccine, but experts cautioned against drawing too much of a distinction between the vaccines because the trials had different endpoints and J&J's was conducted while highly transmissible new variants of the virus were circulating.
Novavax, which is testing its vaccine in South Africa, said it was 60 per cent effective at preventing mild, moderate and severe COVID-19 in patients who did not have HIV. It said about 90 per cent of cases in the study involved the new South African variant. The mid-stage South Africa trial included 4,400 patients.
The vaccine developed by AstraZeneca with Oxford University provided only minimal protection against mild-to-moderate COVID-19 from the South African variant in a relatively small trial. There was no data yet on its effectiveness in preventing severe disease in people who were infected by the variant because the study involved mostly young adults not considered to be at high risk for serious illness.
J&J expects to produce at least a billion doses of its vaccine in 2021 and has signed supply deals for most of that.
The United States agreed to pay more than US$1 billion for 100 million doses and may purchase an additional 200 million doses.
Other deals include 22 million doses for Mexico, 9 million for Colombia, 30 million to the UK, 4 million to South Korea and 400 million for the European Union. It plans to supply 500 million to poorer countries, working with the COVAX alliance.