Pfizer has cleared the next hurdle in the race to get its Covid-19 vaccine approved for emergency use  after the US Food and Drug Administration (FDA) released documents that raised no new issues about its safety or efficacy.

Pfizer and German partner BioNTech submitted data to the FDA last month about their coronavirus vaccine based on data showing the two-dose regimen was 95% effective against Covid-19 and had no major safety issues.

The vaccine's efficacy data met its expectations for emergency use authorisation, FDA staff said in documents released ahead of a Thursday meeting of outside experts to the FDA who will discuss whether to recommend the Pfizer shot for people aged 16 and older.

The agency typically follows the recommendations of its advisory panels but is not required to do so.

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Data from the trial showed that the vaccine began conferring some protection to recipients even before they received the second shot. The agency's staff noted that more data would be needed to assess the potential of a single dose shot.

A two-dose vaccination was highly effective in preventing confirmed cases of Covid-19 at least seven days after the lastdose, FDA staff said.

The experts will discuss whether it was reasonable to believe that the shot may be effective in preventing Covid-19, the briefing documents showed.

The documents were released on the day people in the UK began getting the Pfizer/BioNTech vaccine, the world's first recipients outside of clinical trials.

The FDA staff said there was currently insufficient data to make conclusions about the safety of the vaccine in those less than 16 years of age, pregnant women and those whose immune systems were compromised.

There were a total of six deaths in Pfizer's late-stage trial of the vaccine, with two deaths among patients receiving the vaccine and the rest in those on a placebo, the documents showed.

All deaths represent events that occur in the general population at a similar rate, FDA staff said.

The FDA is expected to decide on whether to authorise the vaccine within days or weeks.