Moderna said on Monday it plans to start clinical trials of an altered booster version of its COVID-19 vaccine aimed at the South African variant after tests showed its authorised vaccine may produce a diminished antibody response.

It will also test an additional booster shot of its authorised vaccine in trials to see if it boosts antibody reaction against the South Africa variant. The current regimen is for two shots four weeks apart.

The company said in a press release that it was being cautious and that the two-dose regimen of the vaccine was still expected to be protective against the South African and other variants detected to date.

The company said the vaccine did not see any impact from the U.K. variant – which has been shown to be more transmissible – in the tests.

The company said it plans to publish data from its tests against the South African and U.K. variants on the website bioRxiv.

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