LOS ANGELES (NYTIMES) - The California state epidemiologist has recommended that the state pause the distribution of more than 330,000 doses of the Moderna vaccine after a "higher than usual" number of people showed signs of a possible severe allergic reaction.

The recommendation comes at a dire moment in California, which is experiencing one of the most acute outbreaks in the nation.

About 40,000 people are testing positive each day - the equivalent of the daily caseload for the entire United States as recently as September - and California's hospital beds are filling up.

The state epidemiologist, Dr Erica Pan, offered few details about what happened but made the recommendation "out of an extreme abundance of caution" after several people who received the vaccine at one community clinic needed medical attention in the span of 24 hours.

Each appeared to experience a possible "severe" allergic reaction, and officials recommended not using other vaccines from that batch until an investigation was completed, the health department said in a statement Sunday (Jan 17).

According to the Centres for Disease Control and Prevention, an example of a severe allergic reaction is if a patient needs to go to a hospital or be treated with epinephrine.

California health officials did not respond to a request for comment Monday, and it was not immediately clear how the delay would affect the state's overall rollout of vaccines, which has been choppy and plagued with confusion.

The possible allergic reactions had stemmed from the same batch of Moderna vaccines, which included more than 330,000 doses, among 3.5 million vaccines allocated to the state.

California has distributed less than a third of its allocated vaccines, below the national average, with 2.2 per cent of the state's population having received a first dose, according to a New York Times vaccine tracker.

Allergic reactions are a rare response to some vaccines. Some estimates suggest that for a similar type of coronavirus vaccine, made by Pfizer-BioNTech, the risk of severe allergic reaction is about 1 in 100,000.