Social media posts claim an article warning about an increased risk of heart issues during cold weather is part of a conspiracy to cover up rare cardiovascular illness caused by Covid-19 vaccines. But several studies have shown that falling temperatures can cause stress on the heart, and health authorities and experts say people who remain unvaccinated are at greater risk of contracting the virus and suffering related heart complications.
"Clearly pre conditioning to ignore Adverse Reactions... Don't be fooled," said a December 5, 2021 Facebook post that is no longer available, referring to Covid-19 vaccines and sharing a screenshot of an article headlined: "Researchers Warn That Cold Weather Can Cause Blood Clots & Heart Attacks."
Similar posts appeared on Facebook here, on Instagram here and on Twitter here.
For some, hesitancy to receive a Covid-19 vaccine has been compounded by a wave of misinformation, and user comments on the posts suggest that the shots are unusually dangerous or part of a larger conspiracy theory.
The image shared on social media comes from a December 2 article by NEWS PUNCH warning readers that cold weather can have an impact on a person's health, potentially triggering blood clots or heart attacks.
But contrary to the posts' assertions that the health issues are a cover for problems from vaccination, experts say there is evidence to back up the article's assertions of ties to weather.
"We see several studies with strong correlations to cold weather heart health concerns," Comilla Sasson, vice president for science and innovation for emergency cardiovascular care at the American Heart Association (AHA), said on December 7. "Cold also tends to increase the formation of blood clots."
Sasson explained that there are several reasons the two can be linked, noting that "cold makes arteries constrict," which can "decrease blood flow and delivery of oxygen or raise blood pressure," a risk factor for stroke or cardiac distress.
"Winter also is flu season, and studies have shown an increase in heart attacks shortly after people get the flu," she said, adding that seasonal factors such as stress, overindulgence and seasonal depression can come into play.
According to a December 7 AHA statement, "more people die from heart attacks between December 25th and January 1st than at any other time of the year."
AHA has also reported that "every 1-degree Celsius drop in temperature (that's 1.8 degrees Fahrenheit) came with a 0.49 percent increase in deaths from all causes. Other studies have shown that when temperatures go down, strokes increase."
Several more studies that pre-date the Covid-19 pandemic and have found a link between cold weather and serious heart-related illness can be found here, here and here. And a 2020 study published in the Journal of the American Heart Association found that plaque rupture was highest in winter and lowest in summer.
Myocarditis and pericarditis risk
Rare cases of heart inflammation (myocarditis and pericarditis) following vaccination with mRNA-based jabs such as Pfizer-BioNTech's or Moderna's have been reported. The cases have occurred more often in male adolescents and young adults, but remain a rare adverse event.
The US Centers for Disease Control and Prevention said that it is carefully monitoring the reports, and found that "most patients with myocarditis or pericarditis who received care responded well to medicine and rest and felt better quickly."
Boback Ziaeian, assistant professor in the division of cardiology at the David Geffen School of Medicine at the University of California, Los Angeles said on December 7 that cardiac events are much more likely to happen when an individual is infected with SARS-CoV-2, and that the vaccines help decrease the risk.
"The magnitude of harm from being exposed to the virus whether unvaccinated or immune-suppressed are far higher for the unvaccinated," Ziaeian said. "The risks from Covid infection is 11 times -- sometimes 30 times -- as high of you having cardiovascular complications, so blood clots, even myocarditis, the risk of are far higher for getting the virus than the vaccines," he said.
AFP Fact Check previously examined false claims about the risk of heart inflammation following a Covid-19 vaccine. A study by the University of Ottawa Heart Institute was withdrawn and its authors said incorrect data "vastly" inflated the incidence of post-vaccine myocarditis.