- The UN health agency has so far approved only the Pfizer-BioNTech vaccine but it is expected to issue approval for the Moderna jab soon.
GENEVA: World Health Organization experts on Tuesday cautiously backed delaying second injections of the Moderna coronavirus vaccine in some situations, as they did for the Pfizer-BioNTech jabs.
The WHO's Strategic Advisory Group of Experts on Immunisation (SAGE) also insisted international travellers should not be prioritised for any Covid-19 jabs for the time being.
During a meeting last week, the experts discussed the Moderna vaccine which, like that of Pfizer-BioNTech, uses mRNA technology and is being rolled out across the world.
Both vaccines require boosters after three to four weeks, but several countries facing limited vaccine supplies have said they will delay administering the second injection so that more people can benefit from receiving a first dose.
The WHO's vaccine advisory group said it was best to respect the tested intervals between doses of 21 days in the case of the Pfizer-BioNTech vaccine and 28 days for Moderna.
But earlier this month, it said that in "exceptional circumstances" it was possible to wait for up to 42 days to administer the second dose of the Pfizer-BioNTech vaccine -- and on Tuesday, it said the same for the Moderna jabs.
Head of the SAGE, Alejandro Cravioto, warned in a virtual press briefing though that "the evidence we have does not go beyond that" six-week cut off.
The UN health agency has so far approved only the Pfizer-BioNTech vaccine but it is expected to issue approval for the Moderna jab soon.
"We're working with Moderna to go as quickly as possible," WHO's vaccines chief Kate O'Brien told the online briefing.
The two vaccines are very similar, the experts said, except for the storage requirements, with the Pfizer-BioNTech jab needed to be stored at -70 degrees Celsius (-94 degrees Fahrenheit), while Moderna doses can be stored at -20 C.
With vaccine supplies still limited, the WHO has called for health workers and the most vulnerable to be prioritised and SAGE reinforced the message on Tuesday.
"In the current period of very limited vaccine supply, preferential vaccination of international travellers would counter the principle of equity," SAGE said.
"Because of this, and the lack of evidence that vaccination reduces the risk of transmission, SAGE currently does not recommend Covid-19 vaccination of travellers."
SAGE also recommended Tuesday that the Moderna vaccine, like the Pfizer-BioNTech one, should only be administered in settings that can deal with potential anaphylactic reaction.
But the experts stressed this was the usual recommendation for most vaccination programmes, pointing to findings from US health authorities last week indicating that severe allergic reaction to the Moderna vaccine was "rare".
SAGE said there was not enough data to make recommendations on the use of the Moderna jab while breastfeeding or during pregnancy.
And the experts said in situations where there was a shortage of vaccines, people who had been infected with Covid-19 in the previous six months and therefore likely had immunity could opt to postpone vaccination.
But "we are not recommending that programmes exclude individuals on that basis", SAGE executive secretary Joachim Hombach told the briefing.