At an online press conference, from the organization's headquarters in Geneva, in addition to condemning the lack of global solidarity in the administration of vaccines, several officials stressed that there is no scientific data to indicate that an extra dose of the vaccine is needed.

“There is no evidence to indicate the need for a (third) booster dose”, stressed Ann Lindstrand, one of the WHO officials responsible for overseeing vaccination against the new coronavirus, calling on countries considering doing so to think in a global perspective and deliver these doses to countries that have not yet started vaccination.

The official admitted that the vaccine, like any other, can reduce the effects over time, but stressed that there is not enough data yet to indicate that this boost is necessary.

Soumya Swaminathan, WHO's chief scientist, warned that people are considering mixing vaccines and said that there is still little information about the effects (only the use of AstraZeneca vaccine followed by Pfizer is being studied) and that this could result in a “chaotic situation”.

There are four countries that want to do this booster and that requires another 800 million vaccines, said the official, also noting that there is no scientific evidence that this booster is necessary.

"Reinforcement may be needed, in a year or two, but in six months we have no indications," added the chief scientist, urging countries not to trust on statements from pharmaceutical companies, who say a third booster dose is now needed.

Michael Ryan, executive director of the WHO Health Emergencies Program, pointed out that vaccines must be given as a priority to health workers and the most vulnerable populations, because there is a global crisis and it is time to protect these most vulnerable populations.

The global difference in terms of vaccination against Covid-19, with countries already thinking about booster doses and with others where no vaccines have even arrived, also led WHO director-general, Tedros Adhanom Ghebreyesus, to lament: "If solidarity is not working I just find a word for it, greed".

The official said that it is natural that individual interests exists, but he stressed the need for countries to understand that the vaccines they share are also helping them, because that is the only way to put an end to the pandemic.

"We don't understand why the world isn't sharing vaccines, because that was in everyone's interest," he said, adding that what we see is "disappointing" with countries saying they want to buy vaccines that they have money, and where vaccines do not reach.

Tedros Adhanom Ghebreyesus also said that the G20 countries (the world's largest economies) could do more on the issue of vaccines and that they should take this lead.

And he warned that countries that have already vaccinated the population and believe they are safe may be wrong. “When they think it's ok to ignore the rest of the world and the virus continues to circulate, it prolongs the agony of the world,” he said, adding that it was possible to quickly end the covid-19 pandemic, because there are tools for that, like the world did for it.