As vaccination against measles continues to wane, the U.S. has hit a troubling milestone: 2026 has already seen the most confirmed cases of the disease since it was declared eliminated in 2000. Experts predict the tally will only continue to rise as more people question and refuse the measles, mumps, and rubella (MMR) vaccine, or have a harder time getting it. Both are distinct possibilities given President Donald Trump’s recent executive order recommending further changes to the childhood vaccination schedule—including that MMR immunization be split into three single-disease shots, administered across three separate medical visits.
How did we reach this tipping point? And what can be done to return to previous levels of immunization against measles and other diseases to stop deadly outbreaks? Below, K. “Vish” Viswanath, Lee Kum Kee Professor of Health Communication at Harvard T.H. Chan School of Public Health, weighs in.
Q: What generally drives vaccine hesitancy—and refusal?
A: Vaccine hesitancy is not a new phenomenon. It’s been around as long as vaccines have, and many of the foundational motivations have remained similar. People may be concerned about safety and side effects. They may be suspicious of efficacy. They may have cultural or religious reasons. In more recent decades, people may have begun to underestimate the potential threat of the diseases one would get vaccinated against. They may not perceive the risk of being unvaccinated as serious.
Over time, public health leaders and institutions have been quite successful in addressing many of these sources of hesitancy and boosting confidence in vaccines. The majority of people do trust and use them—that’s important not to lose sight of. That said, a few powerful drivers of hesitancy unique to the last five to 10 years have begun to stymie efforts to promote vaccination and help misinformation (the sharing of incorrect information, often unintentionally) and disinformation (the intentional sharing of incorrect information for personal or ideological gain) swirl. One of these drivers is social media: People and groups advocating against vaccination have been able to amplify their views and have become much more organized using social media. And the algorithms driving social media posts increase the chances of exposure to these messages. Another is the disruptions of the COVID-19 pandemic: Criticism of public health actions and guidance and waning trust in public health institutions have given voice and strength to anti-vaccine advocates. Lastly, we have figures of authority questioning, if not actively spreading disinformation about, vaccine safety. Our top government officials are issuing disproven, confusing, dangerous recommendations on childhood vaccinations and promoting harmful myths such as that vaccines are linked to autism, for which there is no evidence.
We need to work to understand why someone may hesitate to get a flu vaccine, or why parents may hesitate to bring their child to the doctor for the MMR vaccine, and address their hesitations with curiosity and empathy.
K. “Vish” Viswanath, Lee Kum Kee Professor of Health Communication
Q: Is there any data available showing rising vaccine hesitancy and its impacts?
A: Our current case numbers for measles and rates of MMR vaccination paint the picture well—one of great, urgent concern. As of Aug. 6, the U.S. confirmed 2,465 measles cases, already the highest annual count in decades. To achieve herd immunity against measles—wherein a critical mass of people have immunity against a disease such that it no longer spreads easily, conferring protection even to the unvaccinated—95% of the population needs to have received their MMR vaccine. Across the country, we’re at 92%, due to pockets of under-vaccination in certain geographic areas and among certain groups. While 10 states have achieved a 95% MMR vaccination rate, the other 40 are somewhere between 85% and 92%. That’s a pretty big missing of the target, and is why this fall, the Pan American Health Organization may vote to revoke the U.S.’s status of having eliminated measles.
The MMR vaccine is particularly interesting to focus on here because it’s a flashpoint in the rise in vaccine hesitancy and refusal. It was specifically the MMR vaccine that a pediatrician from the U.K. linked to autism in a 1998 study published in a peer-reviewed journal. That study was deeply flawed and has since been discredited, but its false claims took root and led to not just a drop in MMR vaccine rates (and therefore a rise in cases), but also, many argue, to increased hesitancy around all childhood vaccines. Today we’re experiencing that spillover effect. We’re hearing our national leaders cite vaccines as the reason for current rates of autism and question the overall safety of the MMR and other vaccines, accelerating the spread of misinformation such that, according to 2025 data from the Kaiser Family Foundation (KFF), one-third of adults report reading or hearing the false claim that getting the MMR vaccine is more dangerous than measles infection itself. That figure was 18% in 2024. KFF data also shows that 16% of parents have skipped or delayed at least one childhood vaccine for any of their children—a rate that fluctuates depending on partisan identity and other sociodemographic factors.
Q: What strategies should public health leaders be using to encourage vaccine uptake and fight mis- and disinformation?
A: I think about improving our public health communications, which I break down into two parts: the message and the messenger. To improve the message, we need to look beyond just scientific facts. We’ve been communicating successfully about the science behind vaccines and the evidence proving their safety and effectiveness. This information is critical, but inadequate on its own. We also need to introduce sympathetic, culturally nuanced communication around values. We need to work to understand why someone may hesitate to get a flu vaccine, or why parents may hesitate to bring their child to the doctor for the MMR vaccine, and address their hesitations with curiosity and empathy. Sometimes in public health our approach is to scold. Not only is that not effective, it’s also not fair: We can’t blame families for what self-interested anti-vaccine groups are doing to sow seeds of doubt and spread disinformation. Nor can we make judgments about people’s religious beliefs or historical experiences, for example, if someone comes from a community that had been experimented upon by the medical establishment.
The messenger is the other important consideration here. In general, but especially during this moment when public health institutions face a crisis in trust, public health leaders need to get their messages out in collaboration with other figures who people still view as credible. That tends to be physicians and other health care professionals—study after study show clearly that most people fall back on the recommendations of their provider. It also tends to be community-based leaders. People trust their faith leader, their community group. We need to equip these trusted sources with information about vaccines and work with them to share it at the local level. I think if we do these things—create stronger messaging and work with trustworthy messengers—accompanied by easing barriers to health care access, we can be very successful.
