The World Health Organization is calling for a moratorium on COVID-19 vaccine boosters until at least the end of September, its head Tedros Adhanom Ghebreyesus said on Wednesday.

The move was to enable that at least 10% of the population of every country was vaccinated, Tedros said.

"I understand the concern of all governments to protect their people from the Delta variant. But we cannot accept countries that have already used most of the global supply of vaccines using even more of it," Tedros added.

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Last week, Israeli President Isaac Herzog received a third shot of coronavirus vaccine, kicking off a campaign to give booster doses to people aged over 60 as part of efforts to slow the spread of the highly contagious Delta variant in the country.

The United States in July signed a deal with Pfizer Inc and German partner BioNTech to buy 200 million additional doses of their COVID-19 vaccines to help with pediatric vaccination as well as possible booster shots.

"We need instead to focus on those people who are most vulnerable, most at risk of severe disease and death, to get their first and second doses," Katherine O'Brien, director, immunization vaccines and biologicals at the WHO, told reporters.