Coronavirus vaccine update | Don't expect first COVID-19 vaccinations until early 2021: WHO

"We're making good progress," Ryan said, noting that several vaccines were now in phase 3 trials and none had failed, so far, in terms of safety or ability to generate an immune response.

"Realistically it is going to be the first part of next year before we start seeing people getting vaccinated," he told a public event on social media.

WHO was working to expand access to potential vaccines and to help scale-up production capacity, Ryan said.

"And we need to be fair about this, because this is a global good. Vaccines for this pandemic are not for the wealthy, they are not for the poor, they are for everybody," he said.

The United States government will pay $1.95 billion to buy 100 million doses of a COVID-19 vaccine being developed by Pfizer Inc and German biotech BioNTech if it proves safe and effective, the companies said.

Ryan also cautioned schools to be careful about re-opening until community transmission of COVID-19 is under control. Debate in the United States over restarting education has intensified, even as the pandemic flares up in dozens of states.

"We have to do everything possible to bring our children back to school, and the most effective thing we can do is to stop the disease in our community," he said. "Because if you control the disease in the community, you can open the schools."

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