Brazil approved Johnson & Johnson's single-dose COVID-19 vaccine for emergency use Wednesday, the fourth vaccine to get regulatory approval in the hard-hit country.

Federal health regulator Anvisa said its board had unanimously approved the vaccine for use on priority groups such as health providers and the elderly.

Brazil signed a deal with the US pharmaceutical giant two weeks ago for 38 million doses of the vaccine, but they will only start arriving in August.

The South American country is struggling to secure enough vaccine doses to immunize its 212 million people, even as an explosion of Covid-19 pushes hospitals to the breaking point.

Brazil also has a deal with Pfizer for 100 million vaccine doses, due to start arriving between April and May.

Brazil is currently applying two vaccines, Oxford/AstraZeneca's and Chinese-developed CoronaVac, both of which require two doses.

With just eight percent of the population having received a first dose and 2.3 percent a second, the country is far off pace to meet the health ministry's goal of immunizing all adults by the end of the year.

That has fueled criticism of far-right President Jair Bolsonaro, who has downplayed the coronavirus threat, refused to purchase various vaccines and said he does not plan to be vaccinated himself.

COVID-19 has claimed more than 321,000 lives in Brazil, second only to the United States, and only shows signs of intensifying until enough vaccines arrive.

Brazil's average daily death toll has more than quadrupled since the start of the year, to 2,976 this week, the highest by far worldwide.

March was Brazil's deadliest month in the pandemic yet by a long shot, with 66,573 people killed by Covid-19, according to health ministry figures.

That was more than double its previous record of 32,881 deaths in July 2020.