Thanks to anti-vaxxers, US goes from measles-free to widespread infection

Vaccines have saved more than 150 million lives over the past five decades.

Mary Van Beusekom, MS

Without a 5% higher measles, mumps, and rubella (MMR) vaccination rate, measles may revert to endemicity in the United States within 25 years, while a 10% decline in vaccination could lead to 11.1 million cases of the highly contagious illness in that timeframe, according to predictions from a simulation model published in JAMA. 

Also, the World Health Organization (WHO); UNICEF; and Gavi, the Vaccine Alliance warn that burgeoning outbreaks of vaccine-preventable diseases threaten to reverse years of progress.

And a study published in Morbidity and Mortality Weekly Report (MMWR) details the ongoing US measles outbreak, which has reached 800 cases.

Measles resurgence looming

The JAMA study, led by Stanford University researchers, involved creation of a large-scale epidemiologic model of the importation and dynamic spread of the vaccine-preventable infectious diseases measles, rubella (German measles), polio, and diphtheria in the United States using childhood vaccination rates from 2004 to 2023. 

The goal was to predict the number of cases and complications (i.e., post measles neurologic conditions, congenital rubella syndrome, paralytic polio, hospitalization, and death) in the next 25 years under current vaccination rates, a 5% rise in vaccination, and a 10% decline.

The model assumed that diseases are imported to the United States by an infected person—most often an unvaccinated US citizen—who has traveled overseas.

"Widespread childhood vaccination has eliminated many infectious diseases in the US," the study authors wrote. "However, vaccination rates are declining, and there are ongoing policy debates to reduce the childhood vaccine schedule, which may risk reemergence of previously eliminated infectious diseases."

At current state-level vaccination rates, measles may reestablish endemicity (83% of simulations; average time to endemicity, 20.9 years), with an estimated 851,300 cases (95% uncertainty interval [UI], 381,300 to 1.3 million cases) in the next 25 years. 

If MMR vaccination declines by 10%, 11.1 million (95% UI, 10.1 million to 12.1 million) cases of measles may occur within 25 years, but a 5% increase in MMR vaccination may keep that number to 5,800 cases (95% UI, 3,100 to 19,400 cases). 

Other vaccine-preventable diseases will not likely reestablish endemicity under current vaccination levels. If routine childhood vaccination fell by 50%, 51.2 million measles cases, 9.9 million cases of rubella, 4.3 million cases of polio, and 197 cases of diphtheria could occur over 25 years. 

Under this scenario, 51,200 cases of post measles neurologic sequelae, 10,700 cases of congenital rubella syndrome, 5,400 cases of paralytic poliomyelitis, 10.3 million hospitalizations, and 159,200 deaths may occur. Measles may become endemic within 4.9 years and rubella by 18.1 years, while polio may return to endemic levels within 19.6 years. 

"We've seen a worrisome pattern of decreasing routine childhood vaccinations," senior author Nathan Lo, MD, PhD, said in a Stanford Medicine press release. "There was a disruption to health care services during the pandemic, but declines preceded this period and have accelerated since then for many reasons." 

"People look around and say, 'We don't see these diseases. Why should we vaccinate against them?'" he added. "There's a general fatigue with vaccines. And there's distrust and misinformation about vaccine effectiveness and safety."

Currently, vaccine-preventable diseases don't spread far, but if fewer people are vaccinated, increasingly larger outbreaks will occur more often until they circulate continually. "With measles, we found that we're already on the precipice of disaster," lead author Matthew Kiang, ScD, said in the release. "Measles is one of the most infectious diseases that exists, so the number of people who have to be immune to prevent it from spreading is extremely high."

Kiang likened travelers who import a disease to matches and undervaccinated US residents the tinder. "With measles, you're throwing a lot of matches in, and eventually something is going to happen," he said.

Amid World Immunization Week, a news release from the WHO, UNICEF, and Gavi sounds the alarm on how low levels of vaccination against vaccine-preventable illnesses threatens to undo years of progress.

"Immunization efforts are under growing threat as misinformation, population growth, humanitarian crises and funding cuts jeopardize progress and leave millions of children, adolescents, and adults at risk," the release said. "Outbreaks of vaccine-preventable diseases such as measles, meningitis, and yellow fever are rising globally, and diseases like diphtheria, that have long been held at bay or virtually disappeared in many countries, are at risk of re-emerging."

To prevent resurgences, the three agencies urge rapid and sustained political attention and investment to strengthen vaccination programs.

A recent WHO accounting of the vaccination supplies in 108 WHO country offices, most in low- and lower–middle-income countries, revealed that nearly half are grappling with moderate to severe disruptions to vaccination campaigns, routine immunization, and access to supplies due to reductions in donor funds. Disease surveillance, including that for vaccine-preventable illnesses, was also disrupted in over half of the countries.

In addition, the number of children missing routine vaccinations has risen in recent years, even as countries work to bring children current with doses they missed during the COVID-19 pandemic. In 2023, roughly14.5 million children worldwide missed all of their routine vaccine doses, up from 13.9 million in 2022 and 12.9 million in 2019. Over half of these children live in countries at risk for health-service disruptions due to conflict, fragility, or instability.

"Vaccines have saved more than 150 million lives over the past five decades," WHO Director-General Tedros Adhanom Ghebreyesus, PhD, said in the release. "Funding cuts to global health have put these hard-won gains in jeopardy. Outbreaks of vaccine-preventable diseases are increasing around the world, putting lives at risk and exposing countries to increased costs in treating diseases and responding to outbreaks."

While the WHO, UNICEF, and Gavi have made huge strides in terms of eliminating certain diseases, lowering the number of infections and related deaths with some illnesses, and stepping up vaccination in Africa, parents, the public, and politicians need to increase their support for vaccination, officials said.

"Gavi's next strategic period has a clear plan to bolster our defences by expanding investments in global vaccine stockpiles and rolling out targeted preventive vaccination in countries most impacted by meningitis, yellow fever and measles," Gavi CEO Sania Nishtar, MD, PhD, said in the release. "These vital activities, however, will be at risk if Gavi is not fully funded for the next five years and we call on our donors to support our mission in the interests of keeping everyone, everywhere, safer from preventable diseases."

Culturally competent community engagement

The MMWR study describes the ongoing US measles outbreak, which is centered in close-knit communities with low vaccine uptake in New Mexico, Oklahoma, and Texas. Eighty-five patients (11%) have been hospitalized, and three died. Last week the outbreak reached 800 cases.

"To prepare for and prevent measles cases and outbreaks, health departments should work with trusted messengers on culturally competent community engagement, education, vaccination efforts, and other infection prevention approaches," the researchers, from the Centers for Disease Control and Prevention and elsewhere, wrote. "Increasing national and local measles, mumps, and rubella vaccination coverage is essential to preventing measles cases and outbreaks."