Boris Johnson is to urge other countries to pledge billions of pounds to fund vaccinations in the poorest countries in the world.
As he opens the Global Vaccine Summit, Mr Johnson will say the move would save millions of lives and protect the world from future outbreaks of infectious diseases.
At least 35 heads of state or government, as well as leaders of private sector organisations and civil society, will take part in the event, designed to raise funds for Gavi, the Vaccine Alliance.
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The summit aims to raise at least £6 billion, to immunise 300 million children by 2025.
The funding will protect children from deadly diseases like polio, diphtheria and measles, as well as help ensure the world can fight coronavirus.
Experts say that vaccinating millions of children against other deadly diseases can free up vital space in healthcare systems to battle the global pandemic. Allowing the virus to spread in developing countries could lead to future waves of infection around the world, reaching countries including the UK, they caution.
Opening the summit, Mr Johnson will express his hope that it becomes “the moment when the world comes together to unite humanity in the fight against disease”.
The UK will contribute £1.65 billion to Gavi over the next five years.
Anne-Marie Trevelyan, the international development secretary, said “The world is quite rightly focusing on responding to the invisible killer that is coronavirus. But we cannot allow this pandemic to disrupt routine immunisation in some of the world’s poorest countries and cause other deadly diseases to spread across the globe.
“We know vaccines work, which is why at today’s summit we need others to step up and pledge funds to Gavi, so it can continue to save the lives of millions of children and protect everyone from infectious diseases.”