The World Health Organization forecasts that people most vulnerable to COVID-19, such as the elderly, will need to get an annual vaccine booster to be protected against variants, an internal document seen by Reuters shows. The estimate is included in a report, which is to be discussed on Thursday at a board meeting of Gavi, a vaccine alliance that co-leads the WHO’s COVID-19 vaccine program COVAX. The forecast is subject to changes and is also paired with two other less likely scenarios. Vaccine makers Moderna Inc and Pfizer Inc, with its German partner BioNTech, have been vocal in their view that the world will soon need booster shots to maintain high levels of immunity, but the evidence for this is 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 general population. It does not say how these conclusions were reached, but shows that under the base scenario new variants would continue to emerge and vaccines would be regularly updated to meet these threats.