Health agency officials said on Wednesday the decision was made for “precautionary reasons”.
They said they had seen data showing “signals” of an increased risk of side effects such as inflammation of the heart muscle or the pericardium.
The pericardium is the double-walled sac containing the heart and the roots of the main vessels.
“We are monitoring the situation closely and are acting rapidly to ensure that Covid-19 vaccinations are constantly as safe as possible, while also providing protection,” Anders Tegnell, Sweden’s chief epidemiologist, said.
Denmark has also temporarily stopped using the Moderna injection in people under the age of 18, citing similar reasons.
Earlier this year, the roll out of the Oxford-AstraZeneca jab was suspended in several European countries amid reports of blood clots.
Subsequent analysis showed the vaccine is associated with a slightly increased but very "rare" risk of some bleeding disorders.
Experts stressed, however, that the risks were rare and comparable with those of other vaccines against conditions such as hepatitis B, measles, mumps and rubella, and flu.
The Oxford-AstraZeneca shot has been approved by the UK’s Medicines and Healthcare products Regulatory Agency and is still used there.
It has not been approved in the US and was pulled from Denmark’s inoculation programme earlier this year.
Johnson & Johnson’s vaccine was also removed from Denmark’s jab roll out.
In July, the European Medicines Agency recommended authorizing Moderna’s Covid vaccine for children ages 12 to 17, the first time the shot has been authorized for people under 18.
Moderna’s vaccine was given the green light for use in anyone 18 and over across the 27-nation European Union in January.
It has also been licensed in countries including Britain, Canada and the US, but so far its use hasn’t been extended to children.
To date, the Pfizer/BioNTech vaccine is the only one approved for children under 18 in Europe and North America.
Millions of Moderna doses have already been administered to adults. In a study of more than 3,700 children ages 12 to 17, the vaccine triggered the same signs of immune protection, and no Covid diagnoses arose in the vaccinated group compared with four cases among those given dummy shots.
Sore arms, headache and fatigue were the most common side effects in the young vaccine recipients, the same ones as for adults.
US and European regulators caution, however, that both the Moderna and Pfizer vaccines appear linked to a rare reaction in teenagers and young adults — chest pain and heart inflammation.
The Swedish health authorities said that the heart symptoms "usually go away on their own," but they must be assessed by a doctor.
The conditions are most common among young men, in connection with, for example, viral infections such as Covid. In 2019, approximately 300 people under the age of 30 were treated in hospital with myocarditis.
Data point to an increased incidence also in connection with vaccination against Covid, mainly in adolescents and young adults and mainly in boys and men.
New preliminary Nordic analyzes indicate that the connection is especially clear when it comes to Moderna’s vaccine, especially after the second dose, the agency said.
"The increase in risk is seen within four weeks after the vaccination, mainly within the first two weeks," it said.
The Swedish agency said the vaccine from Pfizer is recommended for these age groups instead. Its decision to suspend the Moderna vaccine is valid until 1 Dec.
Additional reporting by Associated Press
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