The government announced earlier this month that practices whose supply of flu vaccine had been exhausted would be able to order top-ups from an 8m-dose supply that would be available for delivery in November.
Officials have now confirmed that this supply will include 2.15m doses of Flublok - a vaccine used in the US since 2016 but currently not authorised in the UK.
Government advisors on the joint committee on vaccination and immunisation (JCVI) revealed earlier this year that the government had 'considered products that were not currently licenced in the UK, but which may be gaining a licence in time' for the 2020 flu season as it sought to procude additional vaccine to support an expanded campaign this year.
The JCVI said in June that DHSC officials had informed them that 'final authorisation for Flublok was likely to be in November 2020'.
However, the government has announced that the vaccine has now been granted temporary authorisation by the MHRA. It added that a 'physically and biologically similar vaccine' was recommended for approval by the European Medicines Agency last month.
Deputy CMO Professor Jonathan Van Tam said: 'As we approach the winter and cases of COVID-19 continue to rise, it is crucial we double down on efforts to vaccinate as many people as possible from flu.
'We have increased the number of people eligible for free flu jabs this year to reduce all avoidable risks and protect people from illness.
'Flublok has been in regular use in the United States - and the evidence shows that it is an excellent product. I want to reassure everyone that all vaccines have undergone robust clinical trials and rigorous checks by the regulator to ensure they are safe, effective and of a high quality.'
The government has said it will roll out flu vaccination to more than 30m people this year - double the number usually offered vaccination on the NHS - in the biggest flu campaign in NHS history.
This would include rolling out vaccination to people aged 50-64 years old, but the government has said this cohort will only be offered vaccinations once higher-risk patients are covered and subject to vaccine supplies. GPs have been warned that decisions to roll out vaccination to patients in this age group could be made gradually - potentially one year group at a time.
More than 10m doses of flu vaccine are understood to have been delivered to providers across the UK to date, with the 8m-dose supply secured by the government to follow in November. Officials have said practices would be able to order from that supply in October - but the DHSC has yet to clarify how that will work. A spokesperson said details of how to access this additional stock would be published 'in due course'.