Johnson & Johnson's single-dose COVID-19 vaccine has an overall efficacy of 66 percent, the company said after a huge multi-continent trial, but the shot does not protect as well against a variant first detected in South Africa.
Encouragingly, the vaccine was able to prevent 85 percent of severe COVID-19 cases across all geographical regions – a key indicator lauded by experts.
Its effectiveness against all forms of the disease – mild, moderate and severe – was as high as 72 percent in the United States, but fell to 57 percent in South Africa, where a more transmissible new variant is dominant. In Latin America it was 66 percent effective.
"We're proud to have reached this critical milestone and our commitment to address this global health crisis continues with urgency for everyone, everywhere," the company's CEO Alex Gorsky said.
White House spokeswoman Jen Psaki said President Joe Biden was "encouraged" by the data and the Food and Drug Administration would carry out its own evaluation.
J&J said it would apply for US emergency authorization in early February, and the vaccine will then likely become the third available in the world's hardest-hit country.
The Pfizer and Moderna vaccines were the first to be authorized in the US, and both have efficacies of around 95 percent.
Berlin eyes legal action over vaccine 'favoritism'
Germany's government on Sunday threatened legal action against laboratories failing to deliver coronavirus vaccines to the European Union on schedule, amid tension over delays to deliveries from AstraZeneca.
"If it turns out that companies have not respected their obligations, we will have to decide the legal consequences," Economy Minister Peter Altmaier told German daily Die Welt.
"No company can favor another country over the EU after the fact," he added.
AstraZeneca said it could now only deliver a quarter of the doses originally promised to the bloc for the first quarter of the year because of problems at one of its European factories.
Brussels has implicitly accused AstraZeneca of giving preferential treatment to Britain in the delivery of its vaccine, at the expense of the EU.
Perth under snap lockdown
The Australian city of Perth will begin a snap five-day lockdown after a security guard at a quarantine hotel tested positive for COVID-19, authorities announced Sunday.
Roughly two million residents of the city must stay at home as of Sunday evening, as will those living in the nearby Peel and South West regions.
A scheduled return of schools on Monday will be delayed, with locals only permitted to leave their homes for exercise, medical care, essential work or to buy food.
The new rules follow the first case of community transmission in Western Australia state for 10 months, officials said.
"Our model is to deal with it very, very quickly and harshly… so that we can bring it under control and not have community spread of the virus as you have seen in other countries around the world," state Premier Mark McGowan said.