A massive US-based study involving tens of thousands of veterans has concluded that there is a negligible risk of developing a blood clot from a COVID-19 vaccine.
While the results do little to convince many anti-vaccine supporters of the relative safety of vaccinations, they will hopefully bolster community confidence that vaccines are far safer than the disease they serve. are believed to prevent, which is known to increase the risks of developing venous thromboembolism (VTE).
“This population-based study found only an insignificant risk of VTE after COVID-19 vaccination,” says Peter L. Elkin, MD, first author of the paper as well as professor and chair of the Department of biomedical informatics from the University at Buffalo. .
“Given the significant risk of VTE due to COVID-19 infection, the risk-benefit ratio strongly favored vaccination,” Elkin said.
This has always been the general consensus of experts, and fortunately it has resonated across much of the world, with 9.23 billion doses of COVID-19 vaccines administered worldwide so far.
Of course, negligible does not mean that the risk is zero. Yet any chance of getting blood clots is orders of magnitude higher if you are unvaccinated and infected with SARS-CoV-2, an outcome that is incredibly likely in an unvaccinated population with measures of minimum security in place.
Vaccines are widely credited with helping to mitigate the ongoing COVID-19 pandemic, saving countless lives, and there is ample evidence of their safety and effectiveness.
Yet they have drawn suspicion from anti-vaccine advocates, many of whom point to news that emerged in 2021 about a possible link between COVID-19 vaccines and blood clots.
This concern persists, despite the scant evidence of any significant risk from vaccines, and its prevalence on social media and other public forums suggests that greater clarity could be helpful.
“There were concerns that vaccination against COVID-19 would cause undue harm and that VTE was one of the mechanisms implicated by anti-vaxxers,” Elkin said. “We wanted to know the truth.
To do this, Elkin and his colleagues studied data from 855,686 people, all US military veterans at least 45 years old who had received at least one dose of a SARS-CoV-2 vaccine at least 60 days earlier.
The control group included 321,676 people, also all US veterans of the same age group, but still unvaccinated.
The data comes from the US Department of Veterans Affairs’ National Surveillance Tool and covered a period from January 1, 2020 – which was just before the first known US case of COVID-19 – to March 6, 2022.
The researchers took into account a range of known risk factors for VTE, including age, race, gender and body mass index, to help zero in on any effect of the vaccines.
Vaccinated subjects had a VTE rate of 1.3755 per 1,000 people, according to the study, which is 0.1% higher than the baseline VTE rate of 1.3741 per 1,000 in unvaccinated people.
“The excess risk was about 1.4 cases per million vaccinated patients,” Elkin said. “Given that the rate of VTE with COVID-19 is orders of magnitude higher than the insignificant risk of vaccination, our study reinforces the safety and importance of staying current with COVID-19 vaccinations.”
The slightly higher risk could come from vaccine-induced immune thrombotic thrombocytopenia (VITT), the researchers note, an immune response that alters the quantity and quality of platelets, possibly leading to VTE.
“VITT is now recognized as a rare complication of SARS-CoV-2 vaccines based on adenoviral vectors,” they write, referring to a category that includes COVID-19 vaccines from Janssen (Johnson & Johnson) and AstraZeneca.
The study suggests that this slight increase in risk applies to both adenoviral vector vaccines and mRNA vaccines, including those produced by Moderna and Pfizer. In both cases, according to the researchers, the risk is “insignificant”.
The risk of VTE from actual COVID-19 infection, on the other hand, is not.
VTE is an important consequence of COVID-19, the researchers note, occurring in about 8% of hospitalized patients and 23% of intensive care patients.
Based on 28 days of data from June 21, 2021, these figures suggest that at least 3,203 excess VTE cases related to COVID-19 would have occurred out of the 257,125 new cases of COVID-19 recorded during this period. But if all these people had been vaccinated, the expected number of excess VTE cases becomes less than one (0.36).
“This study shows the power of big data, where we can use electronic health record data in a rigorous way to answer questions that would never be possible to answer properly with a randomized controlled trial, due to the small size of the data. the effect and the need to enroll millions of trial patients,” Elkin said.
“This is an example of how biomedical informatics answers important clinical questions,” he adds, “that can help people recognize the benefits of vaccination against COVID-19 and improve the compliance with this approved clinical guideline”.
The study was published in the Journal of Clinical and Translational Sciences.