The WHO's expert vaccine advisers said Wednesday they could recommend Johnson and Johnson's Covid-19 jab for use in countries where coronavirus variants of concern are circulating.

The vaccine has proven effective "in the countries where there is a high spread of the variants", Alejandro Cravioto, the chair of the World Health Organization's Strategic Advisory Group of Experts (SAGE) on Immunization, told reporters.

"After reviewing the evidence, we have a vaccine that shows to be safe and it shows to have the necessary efficacy to be recommended for use by us in people over the age of 18, without an upper age limit."

The WHO gave its seal of approval to the single-shot J&J vaccine on Friday.

It joins the two-dose Pfizer-BioNTech jab and the AstraZeneca-Oxford vaccines made in India and in South Korea as having been signed off by the WHO.

The jab won approval from the European Union on Thursday. It has also received the green light from regulators in the United States, Canada and South Africa.

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