The estimate is included during a report, which is to be discussed on Thursday at a committee meeting of Gavi, a vaccine alliance that co-leads the WHO's Covid-19 vaccine programme COVAX. The forecast is subject to changes and is additionally paired with two other less likely scenarios.
Vaccine makers Moderna Inc and Pfizer Inc, with its German partner BioNTech, are vocal in their view that the planet will soon need booster shots to take care of high levels of immunity, but the evidence for this is often still unclear.
The document shows that the WHO considers annual boosters for high-risk individuals as its "indicative" baseline scenario, and boosters every two years for the overall population.
It doesn't say how these conclusions were reached, but shows that under the bottom scenario new variants would still emerge and vaccines would be regularly updated to satisfy these threats.
The United Nations agency declined to discuss the content of the interior document while Gavi didn't immediately answer an invitation for comment.
The document, which is dated June 8 and remains "work in progress", also predicts under the bottom case that 12 billion Covid-19 vaccine doses are going to be produced globally next year.
That would be slightly above the forecast of 11 billion doses for this year cited by the International Federation of Pharmaceutical Manufacturers & Associations (IFPMA), signalling that the United Nations agency doesn't expect a big ramp-up of vaccine production in 2022.
The document predicts manufacturing problems, regulatory approval issues and "transition faraway from some technology platforms" as potential drags on supplies next year.
It doesn't signal which technologies might be phased out, but the ecu Union, which has reserved the world's largest volume of Covid-19 vaccines, has bet heavily on shots using messenger RNA (mRNA) technology, like those by Pfizer and Moderna, and has forgone some purchases of viral vector vaccines from AstraZeneca and Johnson & Johnson.
The scenarios are going to be wont to define the WHO's global vaccination strategy and therefore the refore the forecasts may change as new data emerge on the role of boosters and the duration of vaccine protection, Gavi says in another document, also seen by Reuters.
So far about 2.5 billion doses are administered worldwide, mostly in rich countries where over half the population has received a minimum of one dose, whereas in many poorer countries but 1% has been vaccinated, consistent with Gavi's estimates.
This gap could widen next year under the WHO's most pessimistic forecast, because the need for annual boosters could push once more poorer nations to the rear of the queue.
In its worst-case scenario, the United Nations agency says production would be 6 billion doses next year, because of stringent regulation for brand spanking new shots and manufacturing issues with existing ones.
That could be compounded by the necessity for annual boosters for the whole world, and not just the foremost vulnerable, to combat variants and limited duration of protection.
In the more optimistic situation, all vaccines within the pipeline would get authorised and production capacity would build up to about 16 billion doses to satisfy demand. Vaccines would even be shared equitably across the planet .
There would be no need for boosters as vaccines would show strong efficacy against variants and long protection.
