The World Health Organization changed its Covid vaccination recommendations on Tuesday, recommending that people in high-risk groups get an extra dose 12 months after their last “booster” dose, Reuters reported.

WHO defines high-risk groups as the elderly, as well as young people, who pose a significant health risk. For this group, the UN agency recommends an additional dose 6 to 12 months after the previous dose, depending on factors related to each person’s health, such as the level of immunity.

The WHO has identified a group that includes healthy children and adolescents as a “low priority” and urged countries to consider indicators such as disease burden before recommending vaccination for this group.

New guidelines have emerged as countries around the world have adopted alternative strategies for their populations.

Some wealthy countries, such as the UK and Canada, already offer ‘booster’ doses to people at high risk of dying if they contract the coronavirus, 6 months after their last Covid vaccination.

The WHO says this is an option for a special category of people at high risk, but its recommendations should become a global guide to good practice.

The agency also says its experts are no longer recommending additional doses of the vaccine after the initial two-dose regimen plus a “revaccination” for people at “moderate” risk.