The World Health Organisation (WHO) has said that people who are most vulnerable to COVID-19, like the elderly, will need to get a booster shot annually, to be protected against the variants, Reuters reported.

The document does not say how the conclusions were reached but come under the context that under the base scenario new variants would continue to emerge. As a result, vaccines would need to regularly updated to steer clear of the infection.

The forecast is to be discussed at a board meeting of Gavi, a vaccine alliance that co-leads the WHO's COVID-19 vaccine programme COVAX.

Global vaccine makers, including Moderna and Pfizer, have been vocal about the need for booster shots across the world to maintain high levels of immunity, but there is not much evidence to support it.

The document, dated June 8 and still a "work in progress," also says under the base case that 12 billion COVID-19 vaccine doses will be produced globally next year, Reuters reported.

The forecast is slightly higher than the 11 billion doses for this year cited by the International Federation of Pharmaceutical Manufacturers & Associations (IFPMA).

The document also predicts issues in manufacturing, regulatory approvals and transition away from some technology platforms.

However, the forecast is subject to changes and is also paired with two other less likely scenarios.

The forecasts may change as new data emerges on the role of boosters and duration of vaccine production, Reuters reported quoting Gavi.

But less than 1 percent have been vaccinated in poor countries, according to Gavi's estimates.

This gap could widen next year amid the need for vaccine booster shots.

In its worst-case scenario, the UN agency says the production would be 6 billion doses next year, due to manufacturing problems and regulatory hurdles.

In the more optimistic scenario, all the vaccines would get authorised and the production capacity would be scaled up to about 16 billion doses. The vaccines would also be shared equitably among all countries.

The boosters might not be required if the vaccines show strong efficacy against new variants and provide longer protection.

(With inputs from Reuters.)