Only two cases of myocarditis were reported in Israel among 44,000 youngsters aged 12 to 15 who received a third dose of the Pfizer/BioNTech vaccine, the Health Ministry said on Wednesday.
The heart inflammations developed by two male teens were both mild, the ministry said.
Studies have shown that while the Pfizer/BioNTech COVID-19 vaccine marginally increases the risk of heart inflammation, the risk is higher among those infected with the coronavirus.
Israel has played a leading role in studying the effects of COVID-19 vaccines, as the fastest country to roll out two-dose inoculations to a wide population a year ago and one of the first to give third shots as boosters.
It is now administering fourth doses to people over 60, health workers and immunocompromised patients.
The data is being watched closely by other countries, including the United States, where the US Food and Drug Administration on Monday authorized the use of a third dose of the Pfizer and BioNTech COVID-19 vaccine for 12-15-year-olds.
An advisory panel to the US Centers for Disease Control and Prevention (CDC) is due to meet on Wednesday to discuss boosters for that age group.
Around 60% of Israel's 9.4 million population is fully vaccinated, nearly all with the Pfizer/BioNTech shot, meaning they have either had three doses or are within six months of their second dose.
The Health Ministry on Wednesday changed its testing and quarantine regulations in what it described as an effort to protect vulnerable populations as infections fueled by the Omicron coronavirus variant have soared.
Daily cases hit a record high on Tuesday with nearly 12,000 infections reported and they are expected to continue rising over the next few weeks. Hospitalizations have also climbed but at a slower pace.