What to know about the mRNA Covid vaccines and risk of heart inflammation in children

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  • Children 12 years and older will be eligible for Covid-19 vaccination from 20 October.
  • They will only receive one dose of the Pfizer vaccine, after international reports suggest a very rare risk of myocarditis after the second jab.
  • This side effect has mostly been seen in male teens and young adults, and the majority of cases were mild and short-lived.

Covid-19 vaccinations will open to children 12 years and older from 20 October, the Department of Health announced during a digital briefing on 15 October.

Increasing South Africa’s vaccination drive to include the 12–17 years age group will add another six million people to the programme, health minister Joe Phaahla said. The department is hoping to vaccinate at least half of these by the start of the school holidays, News24 reported.

However, this age group will receive only one dose of Pfizer's two-dose series, said Phaahla, while experts assess information suggesting that a small number of short-lived cases of myocarditis (inflammation of the heart muscle) occurs after the second dose.

"We can assure parents and young people that even where [cases of myocarditis] have been noticed, there has been no permanent risk. We’re just taking precautions in this case,” said Phaahla.

The South African Product Health Regulatory Authority (Saphra) approved the use of the Pfizer jab in children aged 12 years and older in September 2021, after receiving updated safety and efficacy information from its manufacturers.

The programme will not be rolled out at schools this year. Instead, children older than 12 years will be eligible for vaccination at all public and private vaccination sites.

We take a look at the safety data on vaccine-induced myocarditis in the younger age group.

What is myocarditis?

Myocarditis is an uncommon disease, according to the National Institute of Health (NIH). It occurs in around 23 per 100 000 people worldwide each year, independently of the jabs.

It is marked by inflammation of the heart muscle as well other changes to the heart muscle cells.

The disease can affect small or large sections of the heart muscle, making it harder for the heart to pump blood normally. This, in turn, can lead to arrhythmias (irregular heartbeat), cardiomyopathy, or heart failure, explains Johns Hopkins Medicine.

What are the causes?

It can be caused by viral or bacterial infections; medicines; or damage to the heart’s tissue or muscle from autoimmune diseases, medicines, environmental factors, or other triggers, notes the NIH.

Research indicates that the SARS-CoV-2 virus, which causes Covid-19 disease, may cause myocarditis. In an article for The Conversation, Australian scientists explain that the inflammation the immune system generates to combat these infections can inadvertently lead to inflammation of the heart.

They add that in the very rare cases of myocarditis observed after Covid vaccination, it’s possible a similar thing might be happening.

“That is, the vaccine causes the immune system to generate some level of inflammation, so it’s prepared to mount a response against SARS-CoV-2, and this inflammation is partially misdirected to the heart. But the risk is very small, and the conditions are treatable,” they wrote.

Fortunately, myocarditis can be treated with medicine (anti-inflammatory drugs such as aspirin and corticosteroids), or surgery. However, mild cases of myocarditis may resolve without treatment.

The link to the vaccine

The mRNA vaccines may be linked with a small increase in the risk of this extremely rare condition. Cases have emerged in the US, UK and Israel where the vaccines have been rolled out to teenagers and adolescents.

The cases have been predominantly seen in young male adolescents and young adults, and more often following the second dose (both vaccines require two doses to offer the best protection against Covid), Health24 reported in May 2021.

Reports suggest that it generally occurs three to four days following vaccination. The majority of cases have been mild and short-lived, where patients recover with simple treatment and rest.

For every million Pfizer second doses given to 12 to 17-year-old boys in the US, around 60 had myocarditis, according to the Centers for Disease Control and Prevention (CDC).

One study, published in September 2021, found that the Pfizer vaccine was associated with an excess risk of myocarditis (one to five events per 100 000 people), Health24 reported. The study was based on the electronic health records of around two million people, aged 16 years and older. But the authors cautioned that the risk of myocarditis was substantially increased with Covid infection itself.

Another recent preprint US study suggested Covid infection could be six times more likely to trigger myocarditis in young men than the vaccine – around 450 cases per million infections.

By 11 June 2021, the CDC had received just over 1 200 reports of myocarditis following the administration of 296 million doses of the mRNA vaccines, which equates to a risk of around one in 240 000 doses. This suggests the risk is extremely rare.

Two latest studies from Israel echoes this, with one suggesting the chance of developing the condition to be about one in 50 000, Nature reported. The study researchers noted that the vast majority of cases were mild, including those in teenage boys and young men.

*For more Covid-19 research, science and news, click here. You can also sign up for our Daily Dose newsletter here.

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