LOS ANGELES — Ellie Zeiler, 17, a TikTok creator with over 10 million followers, received an email in June from Village Marketing, an influencer marketing agency. It said it was reaching out on behalf of another party: the White House.Would Ms. Zeiler, a high school senior who usually posts short fashion and lifestyle videos, be willing, the agency wondered, to participate in a White House-backed campaign encouraging her audience to get vaccinated against the coronavirus?“There is a massive need to grow awareness within the 12-18 age range,” Village Marketing wrote to Ms. Zeiler’s business email. “We’re moving fast and have only a few available slots to fill, so please let us know ASAP.”Ms. Zeiler quickly agreed, joining a broad, personality-driven campaign to confront an increasingly urgent challenge in the fight against the pandemic: vaccinating the youthful masses, who have the lowest inoculation rates of any eligible age group in the United States.Fewer than half of all Americans age 18 to 39 are fully vaccinated, compared with more than two-thirds of those over 50, according to the Centers for Disease Control and Prevention. And about 58 percent of those age 12 through 17 have yet to receive a shot at all.To reach these young people, the White House has enlisted an eclectic army of more than 50 Twitch streamers, YouTubers, TikTokers and the 18-year-old pop star Olivia Rodrigo, all of them with enormous online audiences. State and local governments have begun similar campaigns, in some cases paying “local micro influencers” — those with 5,000 to 100,000 followers — up to $1,000 a month to promote Covid-19 vaccines to their fans.The efforts are in part a counterattack against a rising tide of vaccine misinformation that has flooded the internet, where anti-vaccine activists can be so vociferous that some young creators say they have chosen to remain silent on vaccines to avoid a politicized backlash.“I didn’t worry about the backlash,” said Christina Najjar, 30, a TikTok star known online as Tinx.Alyson Aliano for The New York Times“The anti-vaccine side of the internet is still set on all this vaccine news,” said Samir Mezrahi, the administrator of several “meme pages” such as Kale Salad, which has nearly 4 million followers on Instagram and posts viral videos and other content. “We’re posting about J. Lo and Ben Affleck.”Renee DiResta, a researcher who studies misinformation at the Stanford Internet Observatory, said that while influencer campaigns can be useful, they may be no match for mass, organic online movements. She noted the contrast between creators who have been asked to spread pro-vaccine messaging versus vaccine skeptics, who have made it a personal mission to question the injections..css-1xzcza9{list-style-type:disc;padding-inline-start:1em;}.css-3btd0c{font-family:nyt-franklin,helvetica,arial,sans-serif;font-size:1rem;line-height:1.375rem;color:#333;margin-bottom:0.78125rem;}@media (min-width:740px){.css-3btd0c{font-size:1.0625rem;line-height:1.5rem;margin-bottom:0.9375rem;}}.css-3btd0c strong{font-weight:600;}.css-3btd0c em{font-style:italic;}.css-w739ur{margin:0 auto 5px;font-family:nyt-franklin,helvetica,arial,sans-serif;font-weight:700;font-size:1.125rem;line-height:1.3125rem;color:#121212;}#NYT_BELOW_MAIN_CONTENT_REGION .css-w739ur{font-family:nyt-cheltenham,georgia,’times new roman’,times,serif;font-weight:700;font-size:1.375rem;line-height:1.625rem;}@media (min-width:740px){#NYT_BELOW_MAIN_CONTENT_REGION .css-w739ur{font-size:1.6875rem;line-height:1.875rem;}}@media (min-width:740px){.css-w739ur{font-size:1.25rem;line-height:1.4375rem;}}.css-9s9ecg{margin-bottom:15px;}.css-uf1ume{display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-box-pack:justify;-webkit-justify-content:space-between;-ms-flex-pack:justify;justify-content:space-between;}.css-wxi1cx{display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-flex-direction:column;-ms-flex-direction:column;flex-direction:column;-webkit-align-self:flex-end;-ms-flex-item-align:end;align-self:flex-end;}.css-12vbvwq{background-color:white;border:1px solid #e2e2e2;width:calc(100% – 40px);max-width:600px;margin:1.5rem auto 1.9rem;padding:15px;box-sizing:border-box;}@media (min-width:740px){.css-12vbvwq{padding:20px;width:100%;}}.css-12vbvwq:focus{outline:1px solid #e2e2e2;}#NYT_BELOW_MAIN_CONTENT_REGION .css-12vbvwq{border:none;padding:10px 0 0;border-top:2px solid #121212;}.css-12vbvwq[data-truncated] .css-rdoyk0{-webkit-transform:rotate(0deg);-ms-transform:rotate(0deg);transform:rotate(0deg);}.css-12vbvwq[data-truncated] .css-eb027h{max-height:300px;overflow:hidden;-webkit-transition:none;transition:none;}.css-12vbvwq[data-truncated] .css-5gimkt:after{content:’See more’;}.css-12vbvwq[data-truncated] .css-6mllg9{opacity:1;}.css-qjk116{margin:0 auto;overflow:hidden;}.css-qjk116 strong{font-weight:700;}.css-qjk116 em{font-style:italic;}.css-qjk116 a{color:#326891;-webkit-text-decoration:underline;text-decoration:underline;text-underline-offset:1px;-webkit-text-decoration-thickness:1px;text-decoration-thickness:1px;-webkit-text-decoration-color:#326891;text-decoration-color:#326891;}.css-qjk116 a:visited{color:#326891;-webkit-text-decoration-color:#326891;text-decoration-color:#326891;}.css-qjk116 a:hover{-webkit-text-decoration:none;text-decoration:none;}“That’s the asymmetric passion,” she said. “People who believe it’s going to hurt you are out there talking about it everyday. They’re driving hashtags and pushing content and doing everything they can do.”But even if the influencer campaigns amount to a sprinkler in a wildfire, some creators said, they felt compelled to join in.“I didn’t worry about the backlash,” said Christina Najjar, 30, a TikTok star known online as Tinx. “Helping spread the word about the importance of getting vaccinated was the right thing to do.”Ms. Najjar said she was thrilled when the White House reached out to her through her manager in June. She soon posted a question-and-answer video about the vaccines with Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, on Instagram.Their banter was light. Discussing what she called a “happy vaxx girl summer,” Ms. Najjar peppered Dr. Fauci with questions: Was it safe to go out for a drink? Should we be concerned about getting pregnant after getting the vaccine? Do I look 26? “You have an ageless look to you,” he replied.“I’ll tell my Botox doctor that,” she said.Ms. Najjar called the session “a great time,” adding, “I think I flirted with Dr. Fauci, but in a respectful way.” A White House official said Dr. Fauci was not available for comment.Public health officials have used celebrities to reach people since Elvis Presley rolled up his sleeve on “The Ed Sullivan Show” in 1956 to get the polio vaccine. These days, young people are more likely to trust the advice of their favorite content creator than a mainstream celebrity, according to a 2018 study by the marketing agency MuseFind.As a result, “we need to get an influencer army to push the pro-vaccine message out there,” said Jason Harris, chief executive of the advertising agency Mekanism, which is an authority on influencer marketing. “That’s the only way we’re going to have loud enough voices on social to drown out all the misinfo that’s happening.”The White House began considering the power of online creators in January, repurposing the influencer marketing tactics that Mr. Biden had used on the campaign trail toward promoting vaccinations, said Rob Flaherty, the White House director of digital strategy.Mr. Flaherty said he and Clarke Humphrey, the White House’s Covid-19 digital director, teamed up with Village Marketing and Made to Save, a national campaign aimed at promoting access to coronavirus vaccines. In June, they hosted several off-the-record briefings over Zoom so online creators could ask questions about the vaccines and how they worked.Since then, the Biden administration has rolled out influencer discussions with Dr. Fauci and brought Ms. Rodrigo to the White House, where she urged people to “actually get to a vaccination site.”The 18-year-old pop star Olivia Rodrigo was recently tapped by the White House to persuade the youthful masses to get vaccinated.White House, via ReutersIn March, the White House also orchestrated an Instagram Live chat between Dr. Fauci and Eugenio Derbez, a Mexican actor with over 16.6 million Instagram followers who had been openly doubtful of the vaccines. During their 37-minute discussion, Mr. Derbez was upfront about his concerns.“What if I get the vaccine, but it doesn’t protect me against the new variant?” he asked. Dr. Fauci acknowledged that the vaccines might not completely shield people from variants, but said, “It’s very, very good at protecting you from getting seriously ill.”.css-1xzcza9{list-style-type:disc;padding-inline-start:1em;}.css-3btd0c{font-family:nyt-franklin,helvetica,arial,sans-serif;font-size:1rem;line-height:1.375rem;color:#333;margin-bottom:0.78125rem;}@media (min-width:740px){.css-3btd0c{font-size:1.0625rem;line-height:1.5rem;margin-bottom:0.9375rem;}}.css-3btd0c strong{font-weight:600;}.css-3btd0c em{font-style:italic;}.css-w739ur{margin:0 auto 5px;font-family:nyt-franklin,helvetica,arial,sans-serif;font-weight:700;font-size:1.125rem;line-height:1.3125rem;color:#121212;}#NYT_BELOW_MAIN_CONTENT_REGION .css-w739ur{font-family:nyt-cheltenham,georgia,’times new roman’,times,serif;font-weight:700;font-size:1.375rem;line-height:1.625rem;}@media (min-width:740px){#NYT_BELOW_MAIN_CONTENT_REGION .css-w739ur{font-size:1.6875rem;line-height:1.875rem;}}@media (min-width:740px){.css-w739ur{font-size:1.25rem;line-height:1.4375rem;}}.css-9s9ecg{margin-bottom:15px;}.css-uf1ume{display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-box-pack:justify;-webkit-justify-content:space-between;-ms-flex-pack:justify;justify-content:space-between;}.css-wxi1cx{display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-flex-direction:column;-ms-flex-direction:column;flex-direction:column;-webkit-align-self:flex-end;-ms-flex-item-align:end;align-self:flex-end;}.css-12vbvwq{background-color:white;border:1px solid #e2e2e2;width:calc(100% – 40px);max-width:600px;margin:1.5rem auto 1.9rem;padding:15px;box-sizing:border-box;}@media (min-width:740px){.css-12vbvwq{padding:20px;width:100%;}}.css-12vbvwq:focus{outline:1px solid #e2e2e2;}#NYT_BELOW_MAIN_CONTENT_REGION .css-12vbvwq{border:none;padding:10px 0 0;border-top:2px solid #121212;}.css-12vbvwq[data-truncated] .css-rdoyk0{-webkit-transform:rotate(0deg);-ms-transform:rotate(0deg);transform:rotate(0deg);}.css-12vbvwq[data-truncated] .css-eb027h{max-height:300px;overflow:hidden;-webkit-transition:none;transition:none;}.css-12vbvwq[data-truncated] .css-5gimkt:after{content:’See more’;}.css-12vbvwq[data-truncated] .css-6mllg9{opacity:1;}.css-qjk116{margin:0 auto;overflow:hidden;}.css-qjk116 strong{font-weight:700;}.css-qjk116 em{font-style:italic;}.css-qjk116 a{color:#326891;-webkit-text-decoration:underline;text-decoration:underline;text-underline-offset:1px;-webkit-text-decoration-thickness:1px;text-decoration-thickness:1px;-webkit-text-decoration-color:#326891;text-decoration-color:#326891;}.css-qjk116 a:visited{color:#326891;-webkit-text-decoration-color:#326891;text-decoration-color:#326891;}.css-qjk116 a:hover{-webkit-text-decoration:none;text-decoration:none;}Mr. Flaherty said the whole point of the campaign was to be “a positive information effort.” State and local governments have taken the same approach, though on a smaller scale and sometimes with financial incentives.In February, Colorado awarded a contract worth up to $16.4 million to the Denver-based Idea Marketing, which includes a program to pay creators in the state $400 to $1,000 a month to promote the vaccines.Jessica Bralish, the communications director at Colorado’s public health department, said influencers were being paid because “all too often, diverse communities are asked to reach out to their communities for free. And to be equitable, we know we must compensate people for their work.”As part of the effort, influencers have showed off where on their arms they were injected, using emojis and selfies to punctuate the achievement. “I joined the Pfizer club,” Ashley Cummins, a fashion and style influencer in Boulder, Colo., recently announced in a smiling selfie while holding her vaccine card. She added a mask emoji and an applause emoji.“Woohoo! This is so exciting!” one fan commented.Posts by creators in the campaign carry a disclosure that reads “paid partnership with Colorado Dept. of Public Health and Environment.”Patricia Lepiani, president of Idea Marketing, said local micro influencers are in demand because they can seem more authentic than national social media stars. “Vaccination campaigns will only be effective if you know your community,” she said.Colorado officials recently said the state has just two months left to use 350,000 doses of stockpiled Covid-19 vaccines before they expire.Other places, including New Jersey, Oklahoma City County and Guildford County, N.C., as well as cities like San Jose, Calif., have worked with the digital marketing agency XOMAD, which identifies local influencers who can help broadcast public health information about the vaccines.Governments’ interest in the campaigns has spiked sharply in the past week, said Rob Perry, chief executive of XOMAD, as concerns have grown about the spread of the Delta variant of the virus. He added that “when large numbers of influencers post in the same time period, vaccination rates go up.”Ms. Zeiler, who signed on to the White House-backed campaign, also had an online conversation with Dr. Anthony S. Fauci in June.Maggie Shannon for The New York TimesFor Ms. Zeiler, the TikTok star, things moved quickly after she signed on to the White House-backed vaccination campaign. In June, she held an online conversation with Dr. Fauci, using the time to squash the false rumor that vaccines cause infertility. It was a conspiracy theory that she had heard from friends and that she had seen videos of on her TikTok “For You” page.“When I saw that I was like, OK, I need to ask him about it,” she said. “It was kind of sad to see him be like, no, that’s not true.”Ms. Zeiler has since used her footage with Dr. Fauci for other platforms, including Instagram, and created original content for YouTube promoting the vaccines. In one 47-second video, she spoke directly into the camera, ticking through the reasons she had gotten vaccinated and why others should too. “Reason one,” she declared, was “you can go wherever you want.”Ms. Zeiler said in an interview that her work was not done. “I know I won’t stop until all my followers are safe and vaccinated,” she said.