OSLO, Oct 22 (Reuters) - Norway will hold off giving children aged 12-15 a second dose of a vaccine against COVID-19 until it has gathered more research, partly due to a rare side effect involving inflammation of the heart, health authorities said on Friday. The Nordic country has so far only recommended using the Pfizer (PFE.N)/BioNTech (22UAy.DE) vaccine to minors. The health ministry said there was no urgency given that children have a low risk of falling seriously ill from COVID-19 and because a single dose of a vaccine offered a protection rate of 85% against the disease for up to 16 weeks. "A second vaccine dose is also linked with a higher risk of pericarditis and myocarditis, especially among young men and boys," the Norwegian Institute of Public Health (FHI) said in a statement. Pericarditis is inflammation of the outer lining of the heart, while myocarditis is inflammation of the heart muscle. The FHI will assess the situation again in early 2022 after it has gathered more information from studies currently being conducted in the Nordics, it said.Norway"s move is akin to Britain"s, which decided in September that this age group would only receive one dose for now. Separately, Norway said it would donate more than 620,000 doses of Moderna (MRNA.O) vaccines it has no use for. The doses will not be given via the COVAX mechanism but via the European Union to third countries. Non-EU member Norway is part of the single European market and has received its vaccines against COVID-19 via the EU.