The head of the World Health Organization called Wednesday for a moratorium on using coronavirus booster shots until the end of the year — or longer.

Dr. Tedros Adhanom Ghebreyesus said that low- and lower-middle-income countries cannot be “the second or third priority” for COVID-19 vaccines, saying their health workers, older people, and other at-risk groups have the same right to be protected as those in wealthier countries.

“I will not stay silent when the companies and countries that control the global supply of vaccines think the world’s poor should be satisfied with leftovers,” Tedros said.

He acknowledged that third doses may be necessary for the most at-risk populations, where there’s evidence of waning immunity – such as immunocompromised people who didn’t respond sufficiently to their initial doses or are no longer producing antibodies.

“But for now, we do not want to see widespread use of boosters for healthy people who are fully vaccinated,” Tedros said.