Almost a quarter of the world's population will not have access to a Covid-19 vaccine until 2022, according to new research.
Experts from the Johns Hopkins Bloomberg School of Public Health in the US said high-income countries have already secured billions of doses, with uncertainty around access for middle and low-income countries.
Writing in the British Medical Journal (BMJ), they noted that, of the 48 Covid-19 vaccines currently in development or approved, 13 manufacturers have entered into agreements for at least 7.48 billion doses.
"High-income countries, including the European Union bloc, have reserved 51% of these doses, or around 3.85 billion doses, though they comprise only 13.7% of the world's population," they said.
"Of the 13 manufacturers, only six have sold to low and middle-income countries."
They said these six include AstraZeneca/Oxford University and Novavax.
The experts warned that, even if manufacturers meet all their production goals, people in poorer countries could face a long wait.
"By the end of 2021 up to 40% of Covid-19 vaccine courses from leading manufacturers might potentially remain for low and middle-income countries - less if high-income countries scale up existing purchases, more if these countries share what they have procured," they said.
"Even if these leading manufacturers were all to succeed in reaching their projected maximum production capacity, nearly a quarter of the world's population would not have access to a vaccine until at least 2022."
The uncertainty over global access to Covid-19 vaccines stems not just from the fact vaccines are still being tested, but from a "failure of governments and vaccine manufacturers to be more transparent and accountable over these arrangements, from fair pricing to equitable allocation", they added.
Covax is an international drive which aims to boost equitable access to Covid-19 tests, treatments and vaccines.
According to the Johns Hopkins researchers, Covax has made initial purchases of 300 million vaccine doses from AstraZeneca/Oxford University, plus an additional 200 million doses from either AstraZeneca/Oxford University or Novavax, all with a ceiling price of $3 (€2.46) per dose.
But this adds up to only a quarter of the at least two billion doses sought by Covax by the end of 2021, they said.
"This study provides an overview of how high-income countries have secured future supplies of Covid-19 vaccines, but that access for the rest of the world is uncertain," the researchers said.
"Governments and manufacturers might provide much needed assurances for equitable allocation of Covid-19 vaccines through greater transparency and accountability over these arrangements."
A second study in the BMJ estimates that 3.7 billion adults worldwide are willing to have a Covid-19 vaccine.