Moderna has said it asked US regulators to authorise its Covid-19 vaccine for children under the age of six.

If approved, it would make it the first jab against the coronavirus available for those under five years old.

The Covid-19 vaccine from Pfizer/BioNTech is authorised for children five and older. But their trial results for two to four-year-olds showed a weaker immune response than in adults, forcing the study to be extended to test a third dose. Pfizer has said that data would come this month.

"This does represent an important area of unmet need," Moderna Chief Medical Officer Paul Burton said.

"There's no other vaccine, no other therapy, that these little kids can have," Mr Burton said.

"If they do judge the data to be sufficient, I think from a public health perspective, offering it to these children as quickly as possible is the best thing."

Moderna released trial data in March showing that its vaccine was safe and generated a similar immune response in young children as for adults, which was the goal of the study.

The Omicron variant of the coronavirus, which has been shown to evade vaccine immunity compared with earlier versions, was predominant during the pediatric trial.

The pharmaceutical company said two doses were around 37% effective in preventing infections in two to five-year-olds and 51% effective for children ages six months to two years.

Mr Burton did not disclose a time frame for when the US Food and Drug Administration (FDA) was expected to consider the authorisation request.

Top US infectious disease expert Dr Anthony Fauci suggested last week that the FDA hopes to review data from the Pfizer/BioNTech vaccine in the age group alongside the Moderna data.

It is not clear how many U.S. parents of will want to vaccinate their children in the age group.

Only 28% of US children in the five to 11 age group are fully vaccinated, and Covid-19 is often more mild in children than adults.

The US Centers for Disease Control and Prevention (CDC) released data on Tuesday showing that 75% of US children had evidence of prior Covid infection in their blood, much of which occurred during the Omicron surge from December until February.

Still, Mr Burton urged parents to vaccinate their children.

"Covid is a bad disease. These variants now are highly transmissible," he said.

"I do believe that getting vaccinated now should protect these kids: protect them against severe disease, hospitalisation, protect them against the long-term effects of Covid. So it makes sense to get vaccinated," Mr Burton added.

The American Academy of Pediatrics last week urged a swift review of the data in a Twitter post, noting declines in other protections such as masking.

"With no known date for an authorised under five vaccine, we urge data once available to be submitted and reviewed ASAP so that we can offer a safe, effective vaccine to our littlest children."