WASHINGTON (REUTERS) - Johnson & Johnson on Friday (Jan 29) said its single-dose vaccine was 72 per cent effective in preventing Covid-19 in the United States, but a lower rate of 66 per cent was observed globally in the large trial conducted across three continents and against multiple variants.

In the trial of nearly 44,000 volunteers, the level of protection against moderate and severe Covid-19 was 66 per cent in Latin America and just 57 per cent in South Africa, where a particularly worrying variant of the novel coronavirus is circulating.

Those results compare with the high bar set by two authorised vaccines from Pfizer-BioNTech and Moderna, which were around 95 per cent effective in preventing symptomatic illness in pivotal trials when given in two doses. Those trials, however, were conducted mainly in the US and before the broad spread of new variants now under the spotlight.

The top US infectious disease specialist Anthony Fauci said the variations in effectiveness around the world underlined the need to vaccinate as many people as quickly as possible to prevent new variants from emerging.

"It's really a wake up call for us to be nimble and to be able to adjust as this virus will continue for certain to evolve," Dr Fauci said.

J&J's main study goal was the prevention of moderate to severe Covid-19, and the vaccine was 85 per cent effective in stopping severe disease and preventing hospitalisation across all geographies and against multiple variants 28 days after immunisation.

That level of prevention "will potentially protect hundreds of millions of people from serious and fatal outcomes of Covid-19", Dr Paul Stoffels, J&J's chief scientific officer, said in a statement.

The company plans to seek emergency use authorisation from the US Food and Drug Administration next week. J&J has said it plans to deliver one billion doses in 2021 and will produce the vaccine in the US, Europe, South Africa and India.

Public health officials have been counting on the J&J vaccine to increase much-needed supply and simplify the US immunisation campaign.

The United States has an agreement to buy 100 million doses of J&J's vaccine for US$1 billion (S$1.3 billion) and an option of purchasing an additional 200 million doses.

The company said in a statement the vaccine would be ready immediately upon emergency approval but Dr Stoffels declined to specify how many doses.

"Right now, any protection and additional vaccine is great," Dr Walid Gellad, a health policy associate professor at the University of Pittsburgh said.

"The "South Africa" strain is still uncommon in the US and obviously we would want to see higher efficacy, but the key is not only overall efficacy but specifically efficacy against severe disease, hospitalisation, and death," Dr Gellad added.

None of the vaccine recipients in the J&J trial died from Covid-19, compared with five deaths in the placebo group, according to the National Institutes of Health. The NIH said there were three deaths in the vaccine group overall, but none were determined to be from the virus. That compares with 16 deaths overall in the placebo arm.

Unlike the Pfizer-BioNTech and Moderna vaccines, J&J's does not require a second shot weeks after the first or need to be kept frozen, making it a strong candidate for use in parts of the world with weak transportation infrastructure and insufficient cold storage facilities.

South Africa

Several studies have emerged this month showing that a South African variant of the coronavirus has mutated in areas of the virus that are key targets of vaccines, reducing their efficacy.

"What we are learning is there is different efficacy in different parts of the world," Dr Stoffels said in a telephone interview. Importantly, though, in a sub-study of 6,000 volunteers in South Africa, Dr Stoffels said, the J&J vaccine was 89 per cent effective at preventing severe disease.

Ninety-five per cent of cases in the South Africa portion of the trial were infections with the South African variant.

"I am overwhelmed by the fact that this vaccine protected against severe disease even in South Africa," said Professor Glenda Gray, the joint lead investigator of the South African vaccine trial.

Prof Gray, who is the chief executive of the South African Medical Research Council, said this is by far the best vaccine for South Africa to fight the mutant strain and can prevent a large number of hospitalisations and deaths.

A mid-stage trial of a Novovax coronavirus vaccine in South Africa also showed lower efficacy in the country. It proved to be 60 per cent effective among volunteers who didn't have HIV. In a separate, late-stage trial in the UK, the vaccine was 89.3 per cent effective.

In the J&J trial, which was conducted in eight countries, 44 per cent of participants were from the United States, 41 per cent were from Central and South America and 15 per cent were from South Africa.

Slightly more than a-third of the volunteers were over age 60.

There were no serious adverse events among those who received the shot, the company said. Full results will be published in a peer-reviewed journal.

J&J's vaccine uses a common cold virus known as adenovirus type 26 to introduce coronavirus proteins into cells in the body and trigger an immune response.

The Pfizer-BioNTech and Moderna vaccines use a new technology called messenger RNA (mRNA) that requires it to be stored in a freezer.

Vaccine targets

The news of another safe and effective vaccine comes as the US has surpassed 430,000 Covid-19 deaths and with hospitals in many states still struggling to keep up with patients despite recent declines in new infections.

Concerns about fresh surges in the US have also grown due to the presence of a more contagious coronavirus variant first discovered in the UK and news of the arrival of the South African variant on Thursday in South Carolina.

The US vaccination programme got off to a slow start in December and has accelerated to around one million shots per day nationwide.

US President Joe Biden has promised that at least 100 million shots will be administered in his first 100 days in office, but concerns about supply disruptions have added uncertainty to that target.

US trial results for the vaccine from AstraZeneca and Oxford University are expected in early February, opening up the possibility of a fourth vaccine option. It has already been approved in the UK, Europe and many countries based on results of a separate trial.

Novavax is also discussing with the FDA whether its data is sufficient to apply for emergency use authorisation.

J&J is studying the effects of its vaccine given in two doses at two months apart, but results of that trial won't be available until this summer, Dr Stoffels said.