The government of Singapore has become the first to recommend that people who've received the Pfizer or Moderna vaccine should avoid strenuous physical activity after getting their shots, something of urgent importance to gym operators as vaccine programmes continue to roll out around the world.

The warning follows a number of people – mostly young men – suffering from myocarditis (an inflammation of the heart muscle) shortly after receiving the jab.

Singapore’s Health Ministry has now urged residents to avoid strenuous exercise for a week after receiving the first and second dose of all mRNA COVID-19 vaccines.

In a statement, the ministry said: "Given the emerging data on the small risk of myocarditis and pericarditis observed after vaccination with mRNA COVID-19 vaccines, the Expert Committee on COVID-19 Vaccination recommends that all vaccinated persons, in particular adolescents and younger men, who have received any dose of the mRNA COVID-19 vaccines, should avoid any exercise or strenuous physical activity for one week after vaccination.

"During this time, the vaccinated persons should seek medical attention promptly if they develop chest pain, shortness of breath or abnormal heartbeats.

"All doctors should also be vigilant around such clinical presentations after vaccination."

Separately, Israel’s health ministry has said it too has found a small number of heart inflammation cases in young men who had received Pfizer’s COVID-19 vaccine.

In a statement, The European Medicines Agency said heart inflammation was a "very rare" side-effect of the COVID-19 vaccines, but that the benefits of having the jab continue to far outweigh any risks.

"EMA confirms that the benefits of all authorised COVID-19 vaccines continue to outweigh their risks, given the risk of COVID-19 illness and related complications and as scientific evidence shows that they reduce deaths and hospitalisations due to COVID-19," the EMA said.

Myocarditis and pericarditis are inflammatory conditions of the heart.

Symptoms can vary, but often include breathlessness, a forceful heartbeat that may be irregular (palpitations), and chest pain.