Pregnant women are being warned not to take the Moderna vaccine by the World Health Organization (WHO).
Experts at the WHO have urged pregnant women to avoid the vaccine unless they are health workers or at high risk, according to new recommendations.
WHO officials also propose the Moderna jab should be administered in two doses at an interval of 28 days, following a review of vaccine data.
This interval can be extended to 42 days under exceptional circumstances in a country hard hit by coronavirus, the experts added.
The WHO said it does not recommend halving the dose of the Moderna vaccine and also recommended it only be administered in a setting where an allergic reaction can be treated.
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The Moderna vaccine is due to arrive in the UK by spring - however it may be less effective against South African variant.
The pharma giant is looking to develop a booster shot to increase its effectiveness against the mutant form of the virus.
Moderna announced the result of tests saying its vaccine offers protection against all mutations of coronavirus.
Lab tests found that vaccination with its jab produced no significant impact on antibodies against the UK variant.
However there was a six-fold reduction in neutralising antibodies produced against the South African variant.
The UK Government has purchased 17 million doses of the Moderna vaccine - enough to vaccinate 8.5 million people.
