US biotech firm Moderna said Monday it was seeking conditional approval for use of its Covid-19 vaccine on teens in the European Union and Canada, in a boost for inoculation campaigns as the summer begins.

The firm said it also plans to file for emergency approval with the Food and Drug Administration in the United States, where the Pfizer/BioNTech jab is already being administered to adolescents age 12 and up.

"We are pleased to announce that we have submitted for conditional marketing approval of our Covid-19 vaccine with the European Medicines Agency for use in adolescents in the European Union," Moderna CEO Stephane Bancel said.

"We are encouraged that the Moderna Covid-19 vaccine was highly effective at preventing Covid-19 and SARS-CoV-2 infection in adolescents," he said in a statement.

"We have filed for authorization with Health Canada and we will file for an Emergency Use Authorization with the US FDA and regulatory agencies around the world for this important younger age population."

Teens are much less susceptible to Covid than older age groups, and the main reason to vaccinate them is to drive down transmission.

But extremely rare cases of severe Covid can still occur, as can a post-viral complication called multisystem inflammatory syndrome.

The two-shot Moderna regime is around 90 percent effective against symptomatic Covid-19 and 95 percent effective against severe disease.

The vaccine was "generally well tolerated" among adolescents, the company said, adding: "No significant safety concerns have been identified to date."

Last month, the American Academy of Pediatrics called the authorization of the Pfizer Covid vaccine for adolescents an important tool for more schools to return to in-person learning this fall.

Moderna has sought full approval of its vaccine for adults in the United States, joining Pfizer/BioNTech.