Governments around the world are warning their citizens that COVID-19 vaccines present heart risks in some populations. But if Twitter users try to look up similar research, they may receive a warning that the information is “unsafe.”

Japan’s Ministry of Health, Labor and Welfare “raised the alert level for ‘side reactions'” to the Pfizer and Moderna two-shot mRNA vaccines on Dec. 3, according to an English translation of a report by the Japanese Kyodo News Service. Just the News couldn’t find a native English version.

“Serious” symptoms of myocarditis and pericarditis are being reported among the vaccinated “more frequently in young men than usual,” the wire report said. But the ministry still generally recommends vaccination because the benefits outweigh the side effects. Conservative website American Thinker flagged the news.

The heart problem figures are much higher for Moderna than for Pfizer recipients, Japanese broadcaster NHK reported. The Japanese ministry said that as of Nov. 14, for every million males who took the Moderna vaccine, 81.79 ages 10-19 and 48.76 in their 20s developed such symptoms. For Pfizer, those figures are 15.66 and 13.32.

The ministry is requiring hospitals “to report in detail incidents involving people who developed the symptoms within 28 days after being vaccinated,” NHK said.

Japan’s action followed that of several Nordic countries specifically against Moderna vaccines this fall, with differing age and gender restrictions, the Associated Press reported at the time.

Sweden and Norway stopped offering Moderna to all people under age 30, while Denmark only restricted those under 18. Finland followed with a more narrowly tailored restriction for males under 18.

The European Medicines Agency acknowledged as early as June that it was reviewing myocarditis cases in Israel following vaccination with Pfizer’s Cominarty, the sole vaccine fully approved in the U.S. Heart problems generally started within several days of the second dose for males under 30. Similar problems were reported in Europe for “all” COVID vaccines.

The FDA added the heart-inflammation warnings to fact sheets for the mRNA vaccines around the same time.

Moderna disclosed in late October that the FDA was delaying emergency approval of its COVID vaccine for teenagers until early next year to study the heart problems reported in this age group. It won’t even seek emergency use authorization to vaccinate children 6-11 until the review for older children is finished.

It’s not clear that COVID vaccination provides a meaningful benefit for children without preexisting health conditions.

A German study of children’s hospitalization, intensive care unit (ICU) admission and death due to COVID-19 and pediatric inflammatory multisystem syndrome, published Nov. 30 as a preprint awaiting peer review, said it couldn’t calculate a case fatality rate for “primarily healthy children ages 5-11.”

The pediatric researchers couldn’t find any such deaths in Germany, while the ICU admission rate for that age group was 0.2 per 10,000.

Deadline passed to offer correction

Just a day before Japan’s announcement, Twitter started warning users not to read a research abstract on heart problems following mRNA vaccination that was published in the American Heart Association journal Circulation.

The abstract, submitted by California doctor and former cardiac surgeon Steven Gundry, found “dramatic changes” for most of his COVID-vaccinated patients in a blood test that measures early signs of heart problems. The patients’ so-called PULS score jumped from an 11% risk of “acute coronary syndrome” within 5 years to 25%.

Gundry presented his findings to an AHA conference last month, according to the trade publication Cardiology Advisor. The jump was notable because Gundry’s patients — more than 500 men and women ages 28 to 97 — had been taking PULS cardiac tests every three to six months for eight years.

The AHA was apparently spooked after former New York Times journalist Alex Berenson flagged the abstract Nov. 22, a week after the conference ended. (Days earlier, Berenson highlighted nearly 4,000 deaths among 4 million Swedes within two weeks of their second vaccination dose, which he claimed would translate into an annual mortality rate nearly three times the Swedish average.)

Circulation added an “expression of concern” to the abstract, the first step toward possible retraction, Nov. 24.

Beyond a typo misspelling “PULS” as “PLUS,” the abstract has no data on “myocardial T-cell infiltration, there are no statistical analyses for significance provided, and the author is not clear that only anecdotal data was used,” the editorial note says. The journal is working on a “suitable correction.”

AHA told Retraction Watch that it had asked Gundry to submit a correction by 6 p.m. Friday. These “brief summary documents” are just the starting point for “a scientific conversation on the findings, which may then, ultimately, result in a full manuscript published in a peer-reviewed scientific journal,” and AHA “makes no representation or guarantee as to their accuracy or reliability,” an AHA spokesperson wrote.

Dana Lewis, a representative for Gundry, told Just the News Friday afternoon, hours before his deadline, that he would not comment on the controversy.

Reuters purported to fact-check the abstract Nov. 26, claiming it lacked “reliable evidence of a link between mRNA vaccines and heart disease.”

By Dec. 2, Twitter was imposing an “unsafe” interstitial that warns readers the link is “potentially spammy or unsafe” for reasons including “misleading content that could lead to real-world harm.”

Only the link to the study’s main page, shared by verified newspaper columnists, a talk show host and “X Games medalist,” triggers the warning. An alternate link directly to the abstract, widely shared on Twitter by non-verified accounts, does not draw the warning.