COVID-19 patients to be given 2 doses of Pfizer-BioNTech vaccine within 21-28 days period: WHO

The FDA warned that there was a "potential for harm" if people believed they were protected against Covid-19 by a first dose of Pfizer's vaccine for longer than available data demonstrate.

Any dose adjustments could be evaluated in clinical trials, FDA Commissioner Stephen Hahn and Peter Marks, the director of the Center for Biologics Evaluation and Research, said in a statement.

"However, at this time, suggesting changes to the FDA-authorised dosing or schedules of these vaccines is premature and not rooted solidly in the available evidence," they said.

Moderna's Covid-19 vaccine takes two doses given 28 days apart, and the Pfizer/ BioNTech Covid-19 includes two doses given 21 days apart, till now.

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In the US, over 15 million doses of the Covid-19 vaccines have been distributed, but only 4.5 million people have received their first dose.

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