Vaccine shortages are likely to cause problems for "several months", England's chief medical officer has warned, amid fears that emergency healthcare staff at COVID "battle stations" are at risk of burnout.

Professor Chris Whitty said the UK needs to urgently maximise the number of people who are vaccinated, as he defended a shift to prioritize first doses for as many at-risk people as possible.

But he said a lack of global supplies will likely hamper efforts to protect the nation in the first part of 2021.

A letter signed by Professor Whitty and the chief medical officers for Scotland, Wales and Northern Ireland, said: "We have to ensure that we maximise the number of eligible people who receive the vaccine."

"Currently the main barrier to this is vaccine availability, a global issue, and this will remain the case for several months and, importantly, through the critical winter period."

"Vaccine shortage is a reality that cannot be wished away."

The makers of the Pfizer/BioNTech vaccine said they are working flat out to boost production of their COVID-19 vaccine, but they warned there will be gaps in supply until other vaccines are rolled out.

(With input from agencies)