A prolific Twitter account posted Anastasia’s name and smiling dance portrait in a tweet with a syringe emoji. A Facebook user messaged her mother, Jessica Day-Weaver, to call her a “murderer” for having her child vaccinated.

In reality, the Ohio kindergartner had experienced lifelong health problems since her premature birth, including epilepsy, asthma and frequent hospitalizations with respiratory viruses. “The doctors haven’t given us any information other than it was due to all of her chronic conditions. … There was never a thought that it could be from the vaccine,” Day-Weaver said of her daughter’s death.

But those facts didn’t matter online, where Anastasia was swiftly added to a growing list of hundreds of children, teens, athletes and celebrities whose unexpected deaths and injuries have been incorrectly blamed on COVID-19 shots. Using the hashtag #diedsuddenly, online conspiracy theorists have flooded social media with news reports, obituaries and GoFundMe pages in recent months, leaving grieving families to wrestle with the lies.

There’s the 37-year-old Brazilian television host who collapsed live on air because of a congenital heart problem. The 18-year-old unvaccinated bull rider who died from a rare disease. The 32-year-old actress who died from bacterial infection complications.

The use of “died suddenly” — or a misspelled version of it — has surged more than 740% in tweets about vaccines over the past two months compared with the two previous months, the media intelligence firm Zignal Labs found in an analysis conducted for The Associated Press. The phrase’s explosion began with the late November debut of an online “documentary” by the same name, giving power to what experts say is a new and damaging shorthand.

“It’s kind of in-group language, kind of a wink wink, nudge nudge,” said Renee DiResta, technical research manager at the Stanford Internet Observatory. “They’re taking something that is a relatively routine way of describing something — people do, in fact, die unexpectedly — and then by assigning a hashtag to it, they aggregate all of these incidents in one place.”

The campaign causes harm beyond just the internet, epidemiologist Dr. Katelyn Jetelina said.

“The real danger is that it ultimately leads to real world actions such as not vaccinating,” said Jetelina, who tracks and breaks down COVID data for her blog, “Your Local Epidemiologist.”

Rigorous study and real-world evidence from hundreds of millions of administered shots prove that COVID-19 vaccines are safe and effective. Deaths caused by vaccination are extremely rare and the risks associated with not getting vaccinated are far higher than the risks of vaccination. But that hasn’t stopped conspiracy theorists from lobbing a variety of untrue accusations at the vaccines.

The “Died Suddenly” film features a montage of headlines found on Google to falsely suggest they prove that sudden deaths have “never happened like this until now.” The film has amassed more than 20 million views on an alternative video sharing website, and its companion Twitter account posts about more deaths and injuries daily.

An AP review of more than 100 tweets from the account in December and January found that claims about the cases being vaccine related were largely unsubstantiated and, in some cases, contradicted by public information. Some of the people featured died of genetic disorders, drug overdoses, flu complications or suicide. One died in a surfing accident.

The filmmakers did not respond to specific questions from the AP, but instead issued a statement that referenced a “surge in sudden deaths” and a “PROVEN rate of excess deaths,” without providing data.

The number of overall deaths in the U.S. has been higher than what would be expected since the start of the COVID-19 pandemic, in part because of the virus, overdoses and other causes. COVID-19 vaccines prevented nearly 2 million U.S. deaths in just their first year of use.

Some deaths exploited in the film predate the pandemic. California writer Dolores Cruz published an essay in 2022 about grieving for her son, who died in a car crash in 2017. “Died Suddenly” used a screenshot of the headline in the film, portraying his death as vaccine related.

“Without my permission, someone has taken his story to show one side, and I don’t appreciate that,” Cruz said in an interview. “His legacy and memory are being tarnished.”

Others featured in the film survived — but have been forced to watch clips of their medical emergencies misrepresented around the world. For Brazilian TV presenter Rafael Silva, who collapsed while reporting on air because of a congenital heart abnormality, online disinformation prompted a wave of harassment even before the “Died Suddenly” film used the footage.

“I received messages saying that I should have died to serve as an example for other people who were still thinking about getting the vaccine,” Silva said.

Many of the posts online cite no evidence except that the person who died had been vaccinated at some point in the past, using a common disinformation strategy known as post hoc fallacy, according to Jetelina.

“People assume that one thing caused another merely because the first thing preceded the other,” she said.

Some claims about those who’ve suffered heart issues also weaponize a kernel of truth — that COVID-19 vaccines can cause rare heart inflammation issues, myocarditis or pericarditis, especially in young men. Medical experts say these cases are typically mild and the benefits of immunization far outweigh the risks.

The narrative also has leveraged high-profile moments like the collapse of Buffalo Bills safety Damar Hamlin as he suffered cardiac arrest during a game last month after a fierce blow to his chest. But sudden cardiac arrest has long been a prominent cause of death in the U.S. — and medical experts agree the vaccine didn’t cause Hamlin’s injury.

For some families, the misinformation represents a sideshow to their real focus: understanding why their loved ones died and preventing similar tragedies.

Clint Erickson’s son, Tyler, died in September just before his 18th birthday while golfing near their home in Florida. The family knows his heart stopped but still doesn’t know exactly why. Tyler wasn’t vaccinated, but his story appeared in the “Died Suddenly” film nonetheless.

“It bothers me, him being used in that way,” Erickson said. But “the biggest personal issue I have is trying to find an answer or a closure to what caused this.”

Day-Weaver said it was upsetting to see people exploiting her daughter’s death when they knew nothing about her. They didn’t know that she loved people so much she would hug strangers at Walmart, or that she had just learned how to snap.

Still, Day-Weaver said, “I wouldn’t wish the loss of a child on anybody. Even them.”

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Natália Scarabotto in Río de Janeiro contributed to this report.