Moderna defends its vaccine amid questions over heart risks in youth

NEW YORK • Moderna has defended the safety of its Covid-19 shot from questions about associated heart risks in young people.

Chief medical officer Paul Burton acknowledged during a brief conference call on Thursday that its vaccine does appear linked to increased chances of an inflammatory heart condition known as myocarditis in young men.

Moderna maintains that the shot's benefits continue to outweigh the extremely rare risk of myocarditis, he said. The biotech firm's market value has taken a blow on the heart-risk concerns, along with a forecast cut. Its shares plummeted 34 per cent this month through Wednesday's close.

Sweden and Denmark have halted use of Moderna's shot in younger people as they monitor the risk of heart inflammation, while Germany has favoured the vaccine from Pfizer and BioNTech over Moderna's in younger and pregnant people.

Moderna has fallen behind those main rivals in clearances for booster shots and use in children.

Meanwhile, the US Food and Drug Administration has required more time to assess Moderna's emergency request to approve the vaccine in adolescents aged 12 to 17 as it examines the myocarditis risk. The regulatory review may not be completed until January.

That has conceded the US adolescent market largely to Pfizer-BioNTech, which won clearance for those age 12 and up in May.

About 60 per cent of teens have had at least one shot of the Pfizer-BioNTech vaccine, data from the Centres for Disease Control and Prevention shows.

Compared with the Pfizer-BioNTech shot, Moderna's has led to only 10 additional cases of myocarditis per 100,000 inoculations among males age 12 to 29, Mr Burton said in the conference call. The occurrence of the side effect in males suggests the hormone testosterone may be important, he said.

Moderna is also in a legal tussle with the US National Institutes of Health over who gets credit for inventions related to the firm's Covid-19 vaccine.

BLOOMBERG