Top officials at the World Health Organization (WHO) on Tuesday called for COVID-19 vaccines to be shared with poor countries that haven't immunized their people rather than used as booster shots in rich countries.

The WHO also said there's not enough evidence to show that third doses of COVID-19 vaccines are necessary.

At a press briefing, WHO Director-General Tedros Adhanom Ghebreyesus said the world's vaccine disparity was driven by "greed," as he called on drugmakers to prioritize supplying their COVID-19 vaccines to poor countries instead of lobbying rich countries to use even more doses. 

His plea comes as pharmaceutical companies seek authorization for third doses to be used as boosters in some Western countries, including the U.S.

"We are making conscious choices right now not to protect those in need," Tedros said, adding the immediate priority must be to vaccinate people who have yet to receive a single dose.

He called on Pfizer and Moderna to "go all out to supply COVAX, the Africa Vaccine Acquisition Task Team and low and middle-income countries with very little coverage," referring to the U.N.-backed initiative to distribute vaccines globally.

After a 10-week drop in global coronavirus deaths, Tedros said COVID-19 deaths are again beginning to climb and that the extremely infectious Delta variant is "driving catastrophic waves of cases." 

The rich countries have occupied the majority of the vaccines from Pfizer and Moderna as the two companies only agreed to donate small amounts of the doses. About 60 poor countries have encountered stagnant vaccination progress whereby the vaccine suppliers can only provide vaccines for them by the end of the year.

Pfizer met with top U.S. officials on Monday to discuss its plans to seek authorization for a third dose. Last week, the company said the booster could dramatically ramp up immunity and perhaps help ward off worrisome variants – even as U.S. health authorities stressed that fully vaccinated Americans are strongly protected and don't need boosters yet.

"Both Pfizer and the U.S. government share a sense of urgency in staying ahead of the virus that causes COVID-19, and we also agree that the scientific data will dictate next steps," the company said in a statement late Monday.

It's not unusual for manufacturers to brief regulators before filing new data, and a U.S. government spokesperson said the information is just one piece of evidence authorities will use in deciding if, when and for whom a booster might be necessary.

Britain is also considering a possible booster vaccination plan in the fall, which would likely target those over 50 and the most vulnerable.

But WHO's top experts disputed the need for a booster in fully immunized people.

"At this point ... there is no scientific evidence to suggest that boosters are definitely needed," said Dr Soumya Swaminathan, the WHO's chief scientist. Swaminathan said the WHO would make recommendations on booster doses if they were needed, but that any such advice "has to be based on the science and data, not on individual companies declaring that the vaccines should now be administered as a booster dose."

Tom Hart, acting CEO of the ONE campaign, an advocacy group, noted that just one percent of people in poor countries have received even one COVID-19 vaccine dose.

"The idea that a healthy, vaccinated person can get a booster shot before a nurse or grandmother in South Africa can get a single jab is outrageous," he said.

(With input from AP)