Moderna works on booster jab to combat new strain

The drug company said tests showed no impact on results from the UK variant of Covid-19 announced in December but that a six-fold reduction in neutralising titers was found for the South African strain. Levels of titers were still above levels that would be protective, Moderna said.

Moderna said the two-dose application of its vaccine was expected to protect people against emerging strains but that it wanted to be "proactive" in dealing with the virus as it evolves.

The company said it would test a booster dose of its Covid-19 vaccine and was developing an emerging variant booster candidate against the South African strain. Moderna said it expected the boosters to increase neutralising titers for all of the leading vaccine candidates.

Moderna is the first vaccine maker to say it was testing a booster to fight a new variant of the disease after its jab was authorised across the world. The company's shares rose 10.4% to $144.87 at 15:19 GMT.

Stéphane Bancel, Moderna's chief executive, said: “Out of an abundance of caution and leveraging the flexibility of our mRNA platform, we are advancing an emerging variant booster candidate against the variant first identified in the Republic of South Africa into the clinic to determine if it will be more effective to boost titers against this and potentially future variants.”

The discovery of new Covid-19 strains in the UK and South Africa have raised fears that Covid-19 could mutate to become more virulent just as vaccine programmes are being rolled out. The UK said on Sunday the variant that was found in Kent may be more deadly as well as more contagious.

Bancel told the Financial Times he was preparing for a "worst-case scenario despite having no concerns about the vaccine's effectiveness in the next few months. "We cannot be late," he said.