Pfizer and its partner BioNTech have said they will apply for emergency authorisation in the US for their Covid-19 vaccine on Friday.

It will be the job of the US Food and Drug Administration (FDA) to decide if the vaccine is safe to roll out.

It is not clear how long the FDA will take to study the data. However, the US government expects to approve the vaccine in the first half of December.

Data from an advanced trial showed the vaccine protects 94% of adults over 65.

Covid vaccine: Pfizer to apply for authorisation in US https://t.co/m1yGl3Hy0P

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The trial involved 41,000 people worldwide. Half were given the vaccine, and half a placebo.

The UK has pre-ordered 40 million doses and should get 10 million by the end of the year.

Last week, Pfizer and BioNTech published preliminary data suggesting the vaccine offered 90% protection against Covid-19 and said there were no safety concerns. Subsequent data released on Wednesday suggested 95% effectiveness.

This was followed by data on a vaccine made by US company Moderna suggesting nearly 95% protection and similarly promising results from trials of another developed in Russia, called Sputnik.

Prof Stephen Evans, professor of pharmacoepidemiology at the London School of Hygiene & Tropical Medicine (LSHTM), said both the FDA and the European Medicines Agency (EMA) would need to approve the Pfizer data.

"We can expect both agencies to conduct a very careful evaluation and we can rely on their conclusions," he said.

But BBC health correspondent Naomi Grimley says this vaccine is still a long way off widespread use as regulators need to be absolutely sure that it's safe - not least because Moderna and Pfizer both use an experimental technology that has never been approved before.