Speaking to Reuters news agency, the head of the National Institute of Allergy and Infectious Diseases advised against rushing out a Covid-19 vaccine before it has been proven to be safe and effective, reports BBC.

"The one thing that you would not want to see with a vaccine is getting an EUA before you have a signal of efficacy," he said, noting that one of the potential dangers of prematurely letting a vaccine out is that it would make it difficult, if not impossible, for the other vaccines to enroll people in their trial.

"To me, it's absolutely paramount that you definitively show that a vaccine is safe and effective," he added.

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Oxford vaccine triggers immune response

The Oxford vaccine is one of dozens currently under development. Major pharmaceutical companies have launched huge trials to test the effectiveness of their drugs in recent weeks.

Previously the FDA issued an EUA for the drug hydroxychloroquine to treat the virus. But in July officials withdrew the EUA, saying clinical studies suggested the anti-malaria drug was ineffective in treating the virus and failed to prevent infection among those exposed to it.

President Donald Trump is reportedly considering plans to put out a vaccine before it has been fully tested. Such a move could boost his chances of re-election in November's presidential election.

Trump has touted the benefits of the medicine, directly contradicting the advice of his medical experts.

The Financial Times reported the Trump administration was exploring granting emergency use authorisation (EUA) to a vaccine currently under development by the University of Oxford and drug manufacturer AstraZeneca.

Some 10,000 people have volunteered for trials of the drug, but US agencies require trials involving 30,000 people for a vaccine to be authorised.

The US has suffered more confirmed cases and deaths from the coronavirus than any other country. According to Johns Hopkins University, it has recorded more than 5.7 million infections and over 177,000 deaths so far.