The World Health Organization said Tuesday it is no longer recommending additional Covid-19 vaccine booster doses for regular, medium-risk adults as the benefit was marginal.
For such people who have received their primary vaccination course and one booster dose, there is no risk in having further jabs but the returns are slight, the WHO's vaccine experts said.
The UN health agency's Strategic Advisory Group of Experts on Immunisation (Sage) issued updated recommendations after its regular biannual meeting.
Sage's new advice reflects the impact of the dominant Omicron variant of the virus and high-level immunity now achieved in the population through infection and vaccination, the WHO said.
Sage came up with three new, simplified priority categories for Covid vaccination: high, medium and low, based on risk of severe disease or death.
Sage recommended additional booster shots after the first one only for people at the highest risk of developing severe Covid-19 disease.
They include older adults; younger adults with comorbidities such as diabetes, people with immunocompromising conditions like HIV, pregnant women, and frontline health workers.
The medium priority group includes healthy adults, usually under 60, and children and adolescents with comorbidities.
Sage recomends a primary series and a first booster dose.
"When it comes to the medium-risk group, additional booster doses... are no longer recommended," said Sage chair Hanna Nohynek.
"The vaccine is safe and it's efficient against serious disease and death," she said, but for this risk group, while there was no harm in having another shot, "the benefit of these additional boosters is actually quite marginal".
The low priority group includes healthy children and adolescents aged six months to 17 years.
While primary and booster doses are safe and effective for this group, considering the low burden of Covid disease, Sage said countries' vaccination decisions should be based "on contextual factors" such as health programme priorities and cost effectiveness.
Search for new vaccines
As for the impact of Covid-19 vaccines on Long Covid, or post-infection conditions, "the evidence on the extent of their impact is inconsistent", said Sage.
Nearly 13.3 billion Covid vaccine doses have been administered around the world.
WHO vaccines chief Kate O'Brien said that versus Omicron, the existing vaccines provide very good immunity against severe disease, but "frankly they don't last very long for the performance that they do have against mild disease or infection".
The WHO is looking for new Covid vaccines that cover a broad spectrum of variants, have longer durability and better performance against infection and transmission.
It is also seeking vaccines that are move on from injection methods and ultra cold chain storage, O'Brien said, citing nasal, oral and skin patch vaccine methods.
Speaking of two nasally-administered vaccines, particularly one being used in China, Sage executive secretary Joachim Hombach said: "We know that they are immunogenic... but what we really need is data that actually studies the impact on transmission – because that could indeed make a major difference."