FRANCESCO GUARASCIO THE World Health Organization (WHO) 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 programme 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…