(CNN) — Covid-19 vaccines are known to be safe and effective, and they're available for free, but many Americans in the US refuse to get them — and a recent study suggests that celebrities may share some of the blame for people's mistrust.

Celebrities have long tried to positively influence public health, studies show, but during the Covid-19 pandemic, they also seemed to have a large influence on spreading misinformation.

Decades ago, in the 1950s, people could see stars like Elvis Presley, Dick Van Dyke, and Ella Fitzgerald in TV ads that encouraged polio vaccination. This celebrity influence boosted the country's general vaccination efforts, and vaccination nearly eliminated the deadly disease.

In 2021, US officials used celebrities in TV ads to encourage more people to get vaccinated against Covid-19. Big names like lifestyle guru Martha Stewart, singer Charlie Puth, and even Senate Minority Leader Mitchell McConnell showed up in spots that had billions of ad impressions.

The world isn't restricted to only three TV networks any more, so celebrities like actress Hilary Duff, actor Dwayne "The Rock" Johnson, singer Dolly Parton, and even Big Bird also used their enormous presence on Instagram and Twitter to promote a pro Covid-19 vaccine message.

But social media also became a vehicle for celebrities to cast doubt about the safety and effectiveness of the vaccine and even to spread disinformation about Covid.

Their negative messages seemed to find an audience.

For their study, published in the journal BMJ Health & Care Informatics, researchers examined nearly 13 million tweets between January 2020 and March 2022 about Covid-19 and vaccines. They designed a natural language model to determine the sentiment of each tweet and compared them with tweets that also mentioned people in the public eye.

The stars they picked to analyze included people who had shared skepticism about the vaccines, who had Covid-related tweets that were identified as misinformation or who retweeted misinformation about Covid.

They included rapper Nicki Minaj, football player Aaron Rodgers, tennis player Novak Djokovic, singer Eric Clapton, Sen. Rand Paul, former President Donald Trump, Sen. Ted Cruz, Florida Gov. Ron DeSantis, TV host Tucker Carlson, and commentator Joe Rogan.

The researchers found 45,255 tweets from 34,407 unique authors talking about Covid-19 vaccine-related issues. Those tweets generated a total of 16.32 million likes. The tweets from these influencers, overall, were more negative about the vaccine than positive, the study found. These tweets were specifically more related to antivaccine controversy, rather than news about vaccine development, the study said.

The highest number of negative comments was associated with Rodgers and Minaj. Clapton had "very few" positive tweets, the study said, and that may have had an influence, but he also caught flak for it from the public.

The most-liked tweet that mentioned Clapton and the vaccine said, "Strongly disagree with [EC] ... take on Covid and the vaccine and disgusted by his previous white supremacist comments. But if you reference the death of his son to criticize him, you are an ignorant scumbag."

Trump and Cruz were found to have the most substantial impact within this group, with combined likes totaling more than 122,000.

They too came in for criticism on the topic, with many users wondering whether these politicians were qualified to have opinions about the vaccines. The study said the most-liked tweet mentioning Cruz was, "I called Ted Cruz's office asking to make an appointment to talk with the Senator about my blood pressure. They told me that the Senator was not qualified to give medical advice and that I should call my doctor. So I asked them to stop advising about vaccines."

The most-liked tweet associated with Rogan was an antivaxx statement: "I love how the same people who don't want us to listen to Joe Rogan, Aaron Rodgers about the covid vaccine, want us to listen to Big Bird & Elmo."

Posts shared by news anchors and politicians seemed to have the most influence in terms of the most tweets and retweets, the study found.

"Our findings suggest that the presence of consistent patterns of emotional content co-occurring with messaging shared by those persons in the public eye that we've mentioned, influenced public opinion and largely stimulated online public discourse, for the at least over the course of the first two years of the Covid pandemic," said study co-author Brianna White, a research coordinator in the Population Health Intelligence lab at the University of Tennessee Health Science Center — Oak Ridge National Laboratory Center for Biomedical Informatics.

"We also argue that obviously as the risk of severe negative health outcomes increase with the failure to comply with health protective behavior recommendations, that our findings suggest that polarized messages from societal elite may downplay those severe negative health outcome risks."

The study doesn't get into exactly why celebrity tweets would have such an impact on people's attitudes about the vaccine. Dr. Ellen Selkie, who has conducted research on influence at the intersection of social media, celebrity and public health outcomes, said celebrities are influential because they attract a lot of attention.

"I think part of the influence that media have on behavior has to do with the amount of exposure. Just in general, the volume of content that is focused on a specific topic or on a specific sort of interpretation of that topic — in this case misinformation — the repeated exposure to any given thing is going to increase the likelihood that it's going to have an effect," said Selkie, who was not involved in the new research. She is an adolescent health pediatrician and researcher with UW Health Kids and an assistant professor of pediatrics at the University of Wisconsin School of Medicine and Public Health.

Just as people listen to a friend's thoughts, they'll listen to a celebrity whom they tend to like or identify with because they trust their opinion.

"With fandoms, in terms of the relationship between musical artists and actors and their fans, there is this sort of mutual love that fans and artists have for each other, which sort of can approximate that sense that they're looking out for each other," Selkie said.

She said she would be interested to see research on the influence of celebrities who tweeted positive messages about the Covid-19 vaccine.

The authors of the study hope public health leaders will use the findings right away.

"We argue this threat to population health should create a sense of urgency and warrants public health response to identify, develop and implement innovative mitigation strategies," the study says.

Exposure to large amounts of this misinformation can have a lasting impact and work against the public's best interest when it comes to their health.

"As populations grow to trust the influential nature of celebrity activity on social platforms, followers are disarmed and open to persuasion when faced with false information, creating opportunities for dissemination and rapid spread of misinformation and disinformation," the study says.

The-CNN-Wire
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