• People, especially adolescents and younger men, should avoid strenuous activity after either the first or second dose of mRNA vaccines
• The updated advice came from the expert committee on Covid-19 vaccination
• The committee previously issued this advice in relation to the second dose only
• The updated advice came as MOH investigated the collapse of a 16-year-old male six days after he got his first Pfizer-BioNTech dose
• The youth, who engaged in a strenuous gym workout just prior to his collapse, is in critical condition at National University Hospital

SINGAPORE — The expert committee on Covid-19 vaccination is now advising people, especially adolescents and younger men, to avoid exercise or strenuous physical activity for one week after getting any mRNA vaccine dose.

The move comes as the Ministry of Health (MOH) probes the collapse of a 16-year-old male six days after his first Pfizer-BioNTech jab, just after a strenuous gym workout.

He is in critical condition in hospital after suspected cardiac arrest.

Previously, on June 11, the committee had stated that adolescents and younger men should avoid strenuous physical activity for a week after their second dose of the mRNA vaccines. The earlier advice did not relate to the first dose.

The two mRNA vaccines in use here are the Pfizer-BioNTech and Moderna vaccines.

This change has come about due to the “small but nevertheless statistically significant risk” of myocarditis and pericarditis, types of heart inflammation, observed after vaccination with both the first and second mRNA vaccines, the expert committee added in a statement on Monday (July 5). Both the committee and MOH, in a separate release, also noted the case of the 16-year-old.

The youth received his first dose on June 27. On July 3, he worked out with heavy weights above his own body weight prior to what has been preliminarily diagnosed as a cardiac arrest.

The youth is being warded in the intensive care unit at the National University Hospital (NUH), MOH said.

In updating its advice, the expert committee cited a Health Sciences Authority (HSA) update on Monday which said that as of June 30, the authority had received 12 reports of myocarditis and pericarditis occurring in individuals following their vaccinations with mRNA vaccines.

Of the 12 cases, seven of them involved males aged under 30, which was “higher than expected for this age group based on background incidence rates”.

While most of the cases reported had occurred after the second dose, HSA has also started to receive reports of some cases that occurred after the first dose.

The update related to cases reported prior to the 16-year-old who collapsed on Saturday morning and was then taken to Khoo Teck Puat Hospital’s emergency department.

He was transferred to NUH that evening.

Giving more details on the case, MOH said the teenager was "assessed by trained healthcare personnel to be suitable for Covid-19 vaccination, observed on-site for about 30 minutes post-vaccination and was well".

“He was also well for the following five days after vaccination. Prior to his collapse on 3 July, he did weight lifting at the gym. MOH understands that he trains with very heavy weights which were above his body weight,” the statement said.

The ministry said it was in contact with the medical team in NUH, adding that the preliminary diagnosis of his condition is an out-of-hospital cardiac arrest.

“Clinical and laboratory tests are in progress to understand the underlying cause. We will also work with the medical team in NUH to determine if this might be linked to his Covid-19 vaccination,” it added.

“This will include a thorough consideration of whether there was acute severe myocarditis, which is severe inflammation of the heart muscles affecting the heart function, as a possible diagnosis.”

The expert committee said that while most people with vaccine-related myocarditis, both locally and internationally, have mild symptoms and make an uneventful recovery, “it is possible that the condition may be aggravated by factors or strenuous activities that may affect the heart”.

Individuals who are vaccinated are also advised to seek medical attention promptly if they develop chest pain, shortness of breath or abnormal heartbeats, the committee added.