The UN health agency's Strategic Advisory Group of Experts on Immunisation (SAGE) also said over-60s who have been fully immunised with China's Sinovac and Sinopharm vaccine should be offered an additional third Covid-19 vaccine dose.
The experts stressed they were not recommending an additional so-called booster dose for the population at large.
Several Covid-19 vaccines have been given WHO approval for emergency use during the pandemic: Pfizer-BioNTech, Janssen, Moderna, Sinopharm, Sinovac and AstraZeneca.
It is on the verge of deciding whether to give emergency use listing to India's Bharat Biotech jab.
SAGE held a four-day meeting last week to review the latest information and data on a range of vaccines for Covid-19 and other diseases.
"SAGE recommended that moderately and severely immunocompromised persons should be offered an additional dose of all WHO EUL (emergency use listing) Covid-19 vaccines as part of an extended primary series," the group said.
"These individuals are less likely to respond adequately to vaccination following a standard primary vaccine series and are at high risk of severe Covid-19 disease."
It also said that for people fully immunised with Sinovac and Sinopharm vaccines, an additional third dose of the same jab "should be offered to persons aged 60 and above".
A different vaccine "may also be considered based on vaccine supply and access considerations".
SAGE added that when implementing this recommendation, countries should initially aim at maximising two-dose coverage in that population, and thereafter administer the third dose, starting in the oldest age groups. - AFP