Extending the interval between the first two doses of the most widely used COVID-19 vaccines in the country to eight weeks for young men can reduce the rare risk of heart inflammation, U.S. health officials said.

U.S. health officials on Feb. 4 said they are considering lengthening the recommended interval between the first two doses of the most widely used COVID-19 vaccines to eight weeks to lower the risk of heart inflammation and improve their effectiveness.

The U.S. Food and Drug Administration on Jan. 31 gave full approval to Moderna Inc.’s COVID-19 vaccine for people ages 18 and older, making Spikevax the second fully approved vaccine for the virus.

The use of Pfizer Inc. and German partner BioNTech SE’s widely used Covid-19 vaccine marginally increases the risk of heart inflammation, but the risk is higher among those infected with the coronavirus, a study published on Aug. 25 in the New England Journal of Medicine showed.

Three new conditions reported by a small number of people after vaccination with Covid-19 shots from Pfizer and Moderna are being studied to assess if they may be possible side effects, Europe’s drugs regulator said on Aug. 11.

Members of the U.S. military who were vaccinated against Covid-19 showed higher-than-expected rates of heart inflammation, although the condition was still extremely rare, according to a study released on June 29.

Rare cases of heart inflammation in adolescents and young adults is likely linked to vaccination with the Pfizer/BioNTech and Moderna Covid-19 shots, a group of doctors advising the U.S. Centers for Disease Control and Prevention (CDC) said in a presentation released on June 23.

Europe’s drug regulator on June 11 identified another rare blood condition as a potential side effect of AstraZeneca’s Covid-19 vaccine and said it was looking into cases of heart inflammation after inoculation with all coronavirus shots.

Preliminary findings from two vaccine safety monitoring systems suggest a higher-than-expected number of cases of heart inflammation after the second dose of mRNA Covid-19 vaccines in young men, the U.S. Centers for Disease Control and Prevention (CDC) said on June 10.

Some teenagers and young adults who received Covid-19 vaccines experienced heart inflammation, a U.S. Centers for Disease Control and Prevention advisory group said, recommending further study of the rare condition.