Giving booster jabs to people who are already fully vaccinated against coronavirus is like handing out extra life jackets to some while leaving others to drown, a global health leader has warned.
The US has announced a plan to start giving third doses next month.
But millions are being left without any protection while rich countries are preparing to hand out third doses, Dr Michael Ryan of the World Health Organisation (WHO) said.
The science is not yet certain on any potential benefit of third doses, he said, while the organisation’s chief scientist said the “right thing to do” is to wait for the evidence to determine who might need boosters.
The UK Government has said it is awaiting advice from the Joint Committee on Vaccination and Immunisation (JCVI) on any need for booster doses, but Health Secretary Sajid Javid has previously said he anticipates a programme beginning in early September.
Experts have said they are still assessing data before they confirm whether all over-50s and the clinically vulnerable will need a third jab.
America’s Centres for Disease Control and Prevention (CDC) said on Wednesday that it has a plan to start administering booster jabs, subject to an independent evaluation of the safety and effectiveness of a third dose of the Pfizer and Moderna vaccines and recommendations from its Advisory Committee on Immunisation Practices.
In a statement, the CDC said: “We are prepared to offer booster shots for all Americans beginning the week of September 20 and starting eight months after an individual’s second dose.”
It said boosters will likely also be needed for people who had the one-shot Johnson & Johnson vaccine.
The CDC said the data currently available makes “very clear” that protection against the virus begins to decrease over time.
The organisation added: “Based on our latest assessment, the current protection against severe disease, hospitalisation, and death could diminish in the months ahead, especially among those who are at higher risk or were vaccinated during the earlier phases of the vaccination rollout.
“For that reason, we conclude that a booster shot will be needed to maximise vaccine-induced protection and prolong its durability.”
Dr Ryan, who is executive director of the WHO’s health emergencies programme, said: “The reality is right now today, if we think about this in terms of an analogy, we’re planning to hand out extra life jackets to people who already have life jackets, while we’re leaving other people to drown without a single life jacket.
“That’s the reality.
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“Science is not certain on this, there are clearly more data to collect.
“But the fundamental ethical reality is we’re handing out second life jackets while leaving millions and millions of people without anything to protect them.”
WHO chief scientist Dr Soumya Swaminathan said that if all high-income countries decide to give boosters to those in their population who are aged over 50 that will amount to “close to a billion doses”.
She said the “right thing to do” is to “wait for the science to tell us” which groups of people might need boosters and when.
There is a distinction to be made about people who are immunocompromised needing a third dose, she noted, but she said this is a small number of people who “should be protected”.
Of the idea of everyone in high-income countries getting a booster jab, she said: “This is an impossible situation and I’m afraid this will only lead to more variants, to more escape variants, and perhaps we are heading into even more dire situations.”