There were fewer heart attacks and strokes in England, adjusting for risk factors like age, after people were vaccinated against COVID-19 than before, a nationwide study has found. Moreover, the benefits increased with second vaccinations and booster shots. Although the study cannot completely refute the claim that vaccination is associated with an increase in both events, it makes it staggeringly unlikely.

When the conspiracy theory of vaccines containing microchips proved a bit too much for most of the public to fall for, those opposed to vaccines on principle turned to heart attacks and strokes as their main form of fearmongering. Like all the best lies, this had a tiny kernel of truth: A very small number of incidents such as thrombocytopenia did occur soon enough after vaccination that it was considered likely the AstraZeneca vaccine was a cause. The UK restricted vaccinations for most under-40s to Pfizer's one as a result.

Even from the start, the evidence was strong that any risks caused by the vaccines were far outweighed by the risk of the virus itself. This was true even when looking at heart attacks and strokes alone while excluding all the other devastating consequences of infection. Nevertheless, the claim that vaccines are killers has refused to die, resurfacing most recently when AstraZeneca announced they would stop making their vaccine for entirely different reasons.

No amount of evidence will be sufficient for some people, but a new study involving three of the UK’s leading universities has examined the deidentified health records from 45.7 million adults in England to test this myth. The data used covered the period from December 8, 2020, when only a tiny number of people in clinical trials had been vaccinated against COVID-19, and January 23, 2022.

Incidence of arterial thromboses, which covers both heart attacks and strokes, was 10 percent lower in the 13-24 weeks after the first dose of either vaccine used in the UK. This is consistent with widespread previously published evidence, but there has been less research on subsequent vaccinations.

After second and subsequent doses, arterial thromboses fell even more compared to the unvaccinated – by 20 percent for the Pfizer/BioNTech vaccine, and 27 percent for the AstraZeneca vaccine. Similar results apply to other events such as deep venous thrombosis. Whether this makes the decision to not use AstraZeneca among younger people a mistake will require further work to establish.

With almost 97,000 thrombotic events in the average of six months between the start of the study period and first vaccination, reductions like these mean many saved lives.

Studies such as these could always be affected by confounding factors. The authors acknowledge provision of the vaccine to the most vulnerable first might have distorted their results somehow. The odds against such an alternative explanation must be astronomical, however.

"We studied COVID-19 vaccines and cardiovascular disease in nearly 46 million adults in England and found a similar or lower incidence of common cardiovascular diseases, such as heart attacks and strokes, following each vaccination than before or without vaccination,” said study co-first author Dr Samantha Ip of the University of Cambridge in a statement. “This research further supports the large body of evidence on the effectiveness and safety of the COVID-19 vaccination programme, which has been shown to provide protection against severe COVID-19 and saved millions of lives worldwide."

Previously reported increases in myocarditis and pericarditis shortly after receiving the Pfizer/BioNTech vaccine, and the cases of thrombotic thrombocytopenia from AstraZeneca, were real, the study found – but very rare. They were also usually restricted to the first four weeks or less after vaccination. By comparison, severe cardiovascular disease increased after COVID-19 infection. The authors are cautious about concluding that COVID-19 prevention is the reason for the fall in cardiovascular events, but it is certainly the most obvious conclusion.

Failing to get vaccinated out of fears of myocarditis or similar conditions is equivalent to not wearing a seatbelt because of a handful of cases where people became trapped by one, ignoring the demonstrated benefits.

Study co-author professor William Whitely of the University of Edinburgh said; "This England-wide study offers patients reassurance of the cardiovascular safety of first, second and booster doses of COVID-19 vaccines. It demonstrates that the benefits of second and booster doses, with fewer common cardiovascular events including heart attacks and strokes after vaccination, outweigh the very rare cardiovascular complications."

The study is published open access in the journal Nature Communications