A review by US regulators of the single-shot Johnson & Johnson coronavirus vaccine finds it is safe, especially against severe cases.
It paves the way for a third Covid-19 vaccine to be authorised in the US, possibly as early as this weekend.
The vaccine could be a cost-effective alternative to Pfizer and Moderna, as it can be stored in a refrigerator instead of a freezer.
The review was largely positive but more nuanced than for the other two.
The Food and Drug Administration found the Johnson & Johnson vaccine has “known benefits” in reducing both symptomatic and severe illness.
Results from vaccine trials conducted in the US, South Africa and Brazil found its efficacy against the worst outcomes of the virus was “similarly high” but overall protection was lower in South Africa and Brazil, where virus variants have become dominant.
Data showed it was more than 85% effective at preventing serious illness, but only 66% effective overall, when moderate cases were included.
Notably, there were no deaths among participants that received the vaccine and no hospitalisations after 28 days post-vaccine.
An external committee of experts will meet on Friday to recommend whether the FDA should authorise the vaccine, possibly adding to a coming surge in vaccine availability in the US.
On Tuesday, Johnson and Johnson said it could hand over four million doses upon approval of the vaccine.
The company plans to deliver 20 million doses in total by late March, in line with an agreement to supply the US with 100 million doses by the end of June.
Not only will the vaccine require fewer doses than its two-shot Pfizer and Moderna counterparts, it will also require fewer vaccine appointments and medical staff as a result.
Over 65 million Americans have already been vaccinated and about 1.3 million doses are being administered across the country each day.
New cases, hospitalisations and deaths from Covid-19 in the US have all been on the decline over the past few weeks.
Top public health experts, however, continue to warn that mutations of the virus can still threaten progress.