Several countries with high rates of vaccination are already planning COVID-19 booster shots, but some scientists and global health officials believe vaccine supplies should be shared across the world first.
While some Americans may receive a third dose of Pfizer this month, 90 per cent of the entire population of the African continent is yet to receive one shot of vaccine.
There have been warnings about inequitable vaccine distribution since the start of the pandemic.
Experts said if rich countries only protected themselves, ultimately the world would struggle to contain COVID-19.
Now, some key statistics tell a very stark story about how those fears have played out.
- More than 5.7 billion doses of COVID-19 vaccines have been administered across the world, but 73 per cent of those shots have been in just 10 countries
- Just 3 per cent of people in low-income countries have received at least one dose, compared to 60 per cent of people in high-income countries
- The United States has produced enough vaccines to give every American five shots, but African countries are yet to secure enough vaccines for every person
- Among Africa's population of 1.3 billion people, only 4 per cent have been fully vaccinated
So when Africa is so far behind in the global vaccination race, how can some countries start another lap and administer booster shots?
That is a debate that has been playing out inside the White House.
Top US scientists quit over boosters
At a virtual COVID-19 summit at the UN General Assembly on Wednesday, Joe Biden pledged 500 million vaccines to lower-income nations from next year, bringing the total US commitment on vaccine sharing to more than 1 billion jabs.
The announcement came after weeks of debate within the US government about America's moral responsibility to share its abundant supplies with the world.
Top White House figures, including President Biden's chief medical advisor Dr Anthony Fauci, argued America must protect itself first if data showed a third booster shot would be required in the near future.
Dr Fauci wanted booster shots to be on offer to all Americans over 16 from this week, but the US Food and Drug Administration (FDA) only approved an extra jab for those over 65.
Two influential scientists with the FDA recently resigned from their positions amid disagreements with the White House over the need for boosters.
Philip Krause and Marion Gruber later published a scathing critique in academic journal the Lancet, arguing that scientific evidence does not yet justify giving most people third shots.
"The limited supply of these vaccines will save the most lives if made available to people who are at appreciable risk of serious disease and have not yet received any vaccine," they wrote.
"Even if some gain can ultimately be obtained from boosting, it will not outweigh the benefits of providing initial protection to the unvaccinated."
On Thursday, the Australian Technical Advisory Group (ATAGI) on Immunisations said severely immunocompromised people will likely need a third jab to get the full benefits of vaccination, but said this would be part of their primary vaccination program and not considered a "booster".
The debate over booster shots has become the ultimate symbol of inequality during this pandemic.
Africa's 'vaccine famine'
The goal is to vaccinate 40 per cent of people worldwide by the end of this year, and 70 per cent by mid-2022, according to targets set by the World Health Organization (WHO).
But Africa is very unlikely to have enough doses to reach 40 per cent of its population by the end of 2021.
African countries were promised 620 million doses under the COVAX facility by the end of the year, but the supply promise was slashed by 150 million doses.
The 470 million doses expected to arrive will be enough to protect just 17 per cent of the continent.
To reach the 40 per cent target, the number of doses pledged to African countries would need to double by the end of the year and that is assuming all existing promises are delivered on.
African CDC director Dr John Nkengasong said COVAX symbolised the power of global cooperation and "if it was to deliver on its promise, it would have been the best model".
"However, we know how challenging it has been," he said.
Dr Nkengasong said it was important to recognise the "limitations of the multilateral approach" and how regionalism was affecting the success of COVAX.
World Health Organization Africa regional director Matshidiso Moeti said the gap in vaccine equity "was not closing fast enough" and rich countries had a bigger and better role to play.
"Export bans and vaccine hoarding have a chokehold on vaccine supplies to Africa," she said.
Right now, African countries are running low on vaccine supply and many have already run out.
"There is an urgent crisis of vaccine famine on the continent," Dr Nkengasong said.
"You see long lines of people, meandering and winding, in sports stadiums waiting to be vaccinated, but there are no vaccines there."
Achim Steiner from the United Nations Development Program spoke at an event called Vaccines Delayed, Development Denied on the sidelines of the UN General Assembly.
"To date, African countries have expended over 70 per cent of their supply of COVID-19 vaccines and eight countries have exhausted their stocks," he said.
Even when doses do arrive in Africa, the reality is some COVAX shipments arrive with a very short shelf life and countries are forced to throw them away before they can be administered.
"Vaccine distribution has been affected by distribution and storage challenges. This has caused Malawi to destroy over 19,000 doses, for example," Mr Steiner said.
This week, UN secretary-general António Guterres reminded the international community "global vaccination is not philanthropy: it is self-interest" during an address at the General Assembly.
"The larger the pool of unvaccinated people, the more the virus will keep circulating and evolving into new variants — and the greater the economic and social disruption," he said.
"I repeat my call for a global vaccination plan to at least double vaccine production and ensure 2.3 billion doses are equitably distributed through COVAX."
WHO chief Tedros Adhanom Ghebreyesus said it was "unconscionable" some countries were now offering booster shots "while so many people remain unprotected."
As well as donating more doses, richer countries are being called upon to switch places with poorer countries on vaccine manufacturer waiting lists.
India to restart vaccine exports
The rate of serious illness from COVID-19 across Africa has not been as high as many may have predicted.
Experts suggest the younger population, lack of aged-care facilities and the experience the health systems have in dealing with infectious diseases are all a factor.
But Delta has been detected in at least 22 African countries and there are concerns the variant could behave differently.
America's pledge of 500m extra doses will help, but African nations need a lot more vaccines to protect their populations against the spreading virus and to prevent the development of new variants.
India is the world's largest vaccine producer and is a key COVAX supplier.
When the Indian government banned vaccine exports during the country's devastating second wave of infections earlier this year, doses pledged for Africa were not delivered.
That situation is now set to change after India's health minister announced the country would resume exports and donations of surplus COVID-19 vaccines in October.
It's another welcomed move, but several development bodies believe the COVID-19 pandemic has proven that Africa needs to be able to supply its own vaccines.
"We’ve got to build Africa's indigenous manufacturing capacity … we need to secure ourselves," African Development Bank president Akinwumi Adesina said.
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"Africa cannot outsource its health to the rest of the world."