Adults are at a greater risk of developing inflammation of the heart after catching Covid than from a vaccine, research suggests.
A real-world study of more than 2million Israelis found the risks of developing myocarditis following a Covid jab were outweighed by the risks from the virus itself.
Researchers said the condition occurred among fewer than three per every 100,000 patients who got the vaccine and would not have otherwise developed it.
That rate was much higher – 11 per 100,000 – among people infected with the virus, they said.
People who caught the coronavirus were at a much higher risk of developing an irregular heart beat, kidney damage and blocked lung vessels compared to vaccinated participants.
The study warned that the risk of heart inflammation risk was boosted slightly by vaccination, but the complications are still incredibly rare.
The findings only apply to adults. Children on the other hand have been shown to be at a vanishingly small risk of getting sick with Covid in any way.
This is why the UK’s vaccine advisory group has ruled against routinely jabbing young people under 16. They say the tiny risk of side effects is still greater than the risk of Covid.
Researchers in Israel spotted 2.7 extra cases of myocarditis per 100,000 people who were injected with the Pfizer vaccine, but this shot up to 11 additional cases for every 100,000 individuals who caught the virus
The graph shows the number of extra cases of each adverse effect per 100,000 people after a Pfizer injection (grey bars) and a Covid infection (orange bars)
The Covid vaccines went through extensive safety tests before being rolled out to the public, but because trials involve small groups, they often fail to detect extremely rare side effects.
Tests did not pick up cases of myocarditis, but cases of the side effect was recorded in Israel, the US and UK after the countries began vaccinating their populations in the millions.
Most myocarditis cases after Covid vaccines have been identified in young men, which seems to be supported by the study.
Researchers at the Clalit Research Institute in Ramat Gan in Israel examined health records of 2.1million over-16s in Israel to gather data on the real-world cases of adverse effects after a vaccine or a Covid infection.
The country exclusively used the Pfizer jab in its world-leading vaccination drive and was the first to reach 50 per cent uptake.
The experts compared around 880,000 people who were double-jabbed by May 24 with the same number of unvaccinated individuals who had a similar age and health background.
WHAT IS MYOCARDITIS?
Myocarditis is an inflammation of the heart muscle. There are no specific causes of the condition but it is usually triggered by a virus.
Some of the most common infections which cause myocarditis, are those called adenovirus and Coxsackie B.
It can be caused by the common cold, hepatitis B and C, and herpes simplex virus.
The most common symptoms of the condition include chest pain, a fever, a fast heartbeat, tiredness and shortness of breath.
If the inflammation damages the heart muscle or the fibres that conduct electrical pulses to the heart, complications can develop.
They can develop quickly, and include sudden loss of consciousness, an abnormally fast, slow or irregular heartbeat.
In very severe cases the condition is fatal, causing heart failure or sudden death. The inflammation enlarges the heart and creates scar tissue, forcing it to work harder and therefore making it weaker.
In most cases of viral myocarditis, the illness goes away and there are no complications.
But in rare cases when inflammation is severe, there can be damage to the heart which needs monitoring and possibly a heart transplant.
Myocarditis can reoccur, but there is no known way to prevent this. The risk of recurrence is low, around 10 to 15 per cent, according to Myocarditis Foundation.
It is difficult to gauge the prevalence of myocarditis because there is no widely available test for it.
In 2010, approximately 400,000 people died of heart muscle disease – cardiomyopathy that includes myocarditis – worldwide.
Expert consensus opinion estimates that up to 40 per cent of dilated cardiomyopathy results from myocarditis, according to the National Organisation for Rare Disorders.
Their study, which was published yesterday in the New England Journal of Medicine, calculated how many cases of 25 different side effects there were in each group.
They compared these findings to incidences of the adverse effects among 170,000 people who tested positive for Covid and a control group of the same size who did not have the virus.
They spotted around three extra cases of myocarditis per 100,000 people 42 days after they received a second dose of Pfizer.
But among those who tested positive for Covid, the risk shot up to 11 extra cases for every 100,000 individuals.
Myocarditis is usually triggered by a virus and can be fatal in very severe cases, but most of those linked to Covid jabs have been mild.
As of July 28, the UK recorded 256 cases of the condition after dishing out 46.7million jabs.
It is unclear how many cases of the condition there are usually in the general population, because most cases are mild and not well investigated, according to Public Health England.
But among the control group in the study, there was six cases of myocarditis, compared to 21 in those who received a Pfizer jab.
The average age of those who developed the condition after a Pfizer injection was 25, while 91 per cent were male.
The researchers concluded that the Pfizer jab was not associated with an elevated risk of most of the side effects they examined.
There was a chance of developing myocarditis after a Pfizer jab, but this risk was much higher after a Covid infection, they said.
Meanwhile, there was 11 more cases of pericarditis per 100,000 people after a Covid infection, while there was just one extra case per 100,000 people after the Pfizer jab.
Dr Ben Reis, co-author of the study and head of predictive medicine at Boston Children’s Hospital, told the New York Times: ‘Coronavirus is very dangerous, and it’s very dangerous to the human body in many ways.
‘If the reason that someone so far has been hesitating to get the vaccine is fear of this very rare and usually not very serious adverse event called myocarditis, well, this study shows that that very same adverse event is actually associated with a higher risk if you’re not vaccinated and you get infected.’
The study also calcualted there to be 166 extra cases per 100,000 people of arrhythmia – an irregular heartbeat.
Viral illnesses are a common cause of the condition, which can lead to strokes and cardiac arrest.
Meanwhile, researchers spotted six less cases of this condition than they expected among people who got the Pfizer jab.
People who caught the virus were also 125 times more at risk of developing kidney damage.
Researchers also identified 62 more cases of a pulmonary embolism per 100,000 than expected after catching Covid, which is a blocked blood vessel in the lung.
And there was 43 more cases of blood clots in the vein – called deep-vein thrombosis – per 100,000 after testing positive.
Adverse effects linked with the Pfizer jab include 78 more cases than expected of swollen lymph nodes per 100,000 people, which is a common side effect from vaccines.
It comes as the Joint Committee on Vaccination and Immunisation (JCVI), which advises the Government on the vaccine rollout, is determining whether the jabs should be rolled out to younger groups.
Over-16s were invited to get a jab earlier this month, but the scientists are yet to decide whether any younger groups should be offered the vaccine.
But NHS England have been told to prepare to rollout jabs to all over-12s in the coming weeks.
Professor Lawrence Young, a virologist at the University of Warwick, told MailOnline: ‘It’s important to recognise that Covid is a very nasty disease that not only affects your breathing but also your body’s blood clotting system.
‘This can affect other organs such as your heart and kidneys which can lead to long-term damage.
‘The risk associated with Covid infection far outweigh the rare myocarditis associated with the Pfizer vaccine.
‘Most of the reported cases of myocarditis after infection are mild and individuals respond well to standard therapy.’
Professor Robert Storey, an expert in infection, immunity and cardiovascular disease at the University of Sheffield, told MailOnline: ‘Many decisions we make in life influence our health risks and gains.
‘The best chance of a healthy life comes from making decisions that improve our chances of remaining healthy.
‘Covid vaccines are a good example of this.
‘There appear to be very small risks associated with these vaccines with less than roughly 1 in 30,000 risk of heart inflammation with the Pfizer vaccine or 1 in 100,000 risk of blood clots with the AstraZeneca vaccine.
‘These risks of cardiovascular complications are tiny compared to the much higher risks of Covid infection and the rapid spread of the delta variant is clearly a huge danger to people who aren’t vaccinated.
‘Covid infection carries far greater risk and a much higher number of unpleasant complications, including much higher risks of heart inflammation or blood clots.
‘Interestingly, the recent study showed a lower risk of brain haemorrhage amongst other things in people who received the vaccine. So it really emphasises the importance of vaccination in improving your chances of remaining healthy.’