Severe allergic reaction to Moderna's Covid-19 vaccine is “rare,” US health authorities have said, with only 10 cases arising from more than four million first doses.

The Centres for Disease Control and Prevention also emphasised that widespread vaccination was critical to fighting the coronavirus pandemic, according to an AFP report.

“Based on this early monitoring, anaphylaxis after receipt of Moderna Covid-19 vaccine appears to be a rare event,” the CDC said in a report, indicating that none of the reactions resulted in death.

“The clinical and epidemiologic characteristics of anaphylaxis case reports after receipt of Moderna Covid-19 vaccine are similar to those reported after receipt of the Pfizer-BioNTech Covid-19 vaccine,” the CDC said.