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Pfizer Covid vaccine safe for teens – social media posts mangle study results

“A new study has found cardiovascular adverse effects in around a third of teens following Pfizer vaccination, reads a message circulating on social media in August 2022.

It ends with: “This is beyond concerning.”

One version on Facebook has been viewed more than 3,400 times. 

It seems to have originated with a 13 August Twitter post, apparently by a medical doctor, that’s been retweeted more than 11,000 times. The doctor, in turn, appears to have sourced the claim from a Daily Sceptic article posted on 12 August.

Screenshots of the tweet can be seen here, here, here and here on Facebook.

Differently worded versions of the claim can also be found elsewhere on Facebook. One reads: “The Pfizer vaccine is not safe for teens or anyone in my opinion.”

Most of the posts link to a preprint of an academic paper, published online on 8 August, that describes a recent study. The paper is headlined “Cardiovascular Effects of the BNT162b2 mRNA COVID-19 Vaccine in Adolescents”.

Cardiovascular refers to the heart and circulatory system, or blood vessels.

Does the Pfizer-BioNTech mRNA vaccine against Covid-19 really cause adverse cardiovascular effects in a third of teens? And does this mean it is unsafe for them? We looked into it. 


Heart problems after Covid vaccine rare and usually mild

The study described in the preprint was later published, on 28 August, in the journal Tropical Medicine and Infectious Disease.

The study was conducted among 301 students from two schools in Thailand. It found “cardiovascular manifestations” in around a third of the sample who had received the Pfizer Covid vaccine. The social media posts suggest that this means the vaccine is unsafe and should be avoided. That’s not true.

The Thailand study is part of a larger set of research looking at the effects of Covid vaccines on cardiovascular health in teenagers. This comes after the US Centres for Disease Control (CDC) reported in 2021 that there may be a link between mRNA vaccines and effects on the heart, particularly among adolescent males. But the CDC added that although the link exists, these complications are extremely rare. 

Two cases of myocarditis per 100,000 people

Parents may be alarmed at the idea that their children’s heart health could be at risk from the vaccine, but it is important to see study results in context. 

For example, this 2021 study looked at the health records of over 2.5 million vaccinated people in Israel. Only 54 people met the criteria for myocarditis, a kind of inflammation of the heart. Its effects range from no symptoms at all to mild symptoms, and sometimes severe symptoms.

Overall, the study reported that there were 2.13 cases of myocarditis per 100,000 people. To put this in context, the biggest stadiums in the world (like here, here and here) can accommodate around 100,000 people. So if we apply the study’s numbers, two people in an entire stadium might get this complication. And both cases would likely be mild, with the patients recovering quickly. 

The study from Thailand found a higher prevalence of heart complications than the Israeli study. But this also needs a closer look. 

The study reported that “Cardiovascular manifestations were found in 29.24% of patients” – around a third, as claimed in the social media posts. These “manifestations'' included effects like myocarditis, but also tachycardia – the technical term for a fast heart rate – and palpitations – “the feeling of a fast-beating … or pounding heart”, both of which are generally harmless. 

Looking at the numbers, effects like myocarditis and pericarditis (another kind of inflammation of the heart) occurred in just seven of the participants in the study. All seven had “mild symptoms”, and all recovered quickly. 

Contrary to the social media claims being circulated, this data is not anything “concerning”. 

Known Covid health risks outweigh rare vaccine risks

But what is concerning, according to researchers and healthcare organisations around the world, is the effect of Covid infection on the heart. 

“A young person is much more likely to get myocarditis or pericarditis from Covid-19 itself than they would from a Covid-19 vaccine,” said Dr Michelle Johnson, cardiologist at Memorial Sloan Kettering Cancer Center in New York

Researchers in the Thai study also made this point, saying the occurrence of heart issues associated with Covid infection is “much higher, estimated to be 100 times higher” than with mRNA vaccines. 

The CDC constantly monitors cases of cardiovascular and other effects after Covid-19 vaccines. Based on the latest available data, they conclude that the vaccines are safe for all age groups, including adolescents.

They also note that although cardiovascular effects have been reported, these rare effects are far more rare than the heart complications that Covid-19 infection causes. 

“The known risks of Covid-19 illness … far outweigh the potential risks of having a rare adverse reaction to the vaccination."

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