Britain called for temporary ceasefires in wars around the globe to allow millions of the most vulnerable people to receive Covid-19 vaccine injections.
Foreign Secretary Dominic Raab, who led a meeting of the UN Security Council on Wednesday, said 160 million people could miss out on vaccination because of conflict in countries including Yemen, Syria, Somalia and South Sudan.
Failure to inoculate the most at-risk populations could allow the virus to spread and new variants to take hold, making Covid-19 harder to contain.
"Local ceasefires are essential to enable life-saving vaccinations to take place," Mr Raab said.
"And they are essential to protect the brave health workers and humanitarian workers working in incredibly challenging conditions in conflict zones who are striving to deliver that help, that vital lifesaving help to those who need it most.
"Ceasefires have been used to vaccinate the most vulnerable communities in the past, there is no reason we can’t do this, there’s no reason why we can’t with the will that we can muster come together to overcome the challenges."
British officials said a two-day ceasefire in Afghanistan in 2001 allowed thousands of health workers and volunteers to vaccinate 5.7 million children under the age of 5 against polio.
Mr Raab said that it was the responsibility of individual countries to ensure refugees and vulnerable groups were not overlooked. He also pressed for improvements in the storage, delivery and approval of vaccines.
Britain is seeking a UN resolution in coming weeks to support the ceasefire programme, which would include measures to protect people from violence during the process.
“Global vaccination coverage is essential to beating coronavirus,” Mr Raab said.
“That is why the UK is calling for a vaccination ceasefire to allow Covid-19 vaccines to reach people living in conflict zones and for a greater global team effort to deliver equitable access.
“We have a moral duty to act and a strategic necessity to come together to defeat this virus.”
UN Secretary General Antonio Guterres described vaccine equity as “the biggest moral test before the global community” but said distribution had so far been “wildly uneven and unfair”.
“We must ensure that everybody, everywhere can be vaccinated as soon as possible,” he told the online meeting.
Mr Guterres said that those affected by conflict and insecurity were at a particular risk of being left behind.
The coronavirus has infected more than 109 million people and killed at least 2.4 million, but many countries are yet to start vaccination programmes.
About $2.4 billion was raised for the UN-backed Covax campaign to help developing countries that are unable to afford their own stockpiles. But the programme is behind schedule while shots are available to richer nations.
The UK announced on Sunday that it had administered 15 million doses among its population.
The World Health Organisation on Monday granted emergency authorisation for Oxford-AstraZeneca's vaccine to become part of the Covax programme.
The shot developed by Pfizer and BioNTech was approved in December.
The Oxford-AstraZeneca vaccine is authorised in more than 50 countries, including Britain, India, Argentina and Mexico, and is cheaper and easier to distribute than the Pfizer-BioNTech vaccine, which requires ultra-cold storage.