Moderna CEO Stefan Bansel believes existing vaccines will be much less effective against the Omicron strain and warned that it could be months before pharmaceutical companies could produce more vaccines that would work against a new variant of the coronavirus.

Bansel said the large number of Omicron mutations and the rapid spread of the variant in South Africa suggest that existing vaccines may need to be modified next year.

"I do not think there is a chance that the efficiency will be at the same level as we had with the Delta variant. I think there will be a decline. We do not know just how much because we have to wait for the data. "But all the scientists I've talked to say something like 'this is not going to be good.'" Bansel said in an interview with the Financial Times.

Moderna's boss's comments come at a time when public health experts and politicians are trying to get a more optimistic tone about the effectiveness of existing Omicron vaccines.

Bansel says scientists are concerned that 32 of the 50 mutations in the Omicron variant have been found in a "spike protein" that focuses on existing vaccines to boost the immune system against Covid-19.