America is hovering on the brink of a return of endemic measles – a quarter of a century after the disease was declared eradicated in the country, researchers have warned as childhood vaccinations continue to drop nationwide.
At current US routine vaccination rates, measles could return to spreading regularly at high levels, with an estimated 851 300 cases over the next 25 years, suggested computer models used by the researchers.
If rates of vaccination with the measles-mumps-rubella, or MMR, shot were to decline by 10%, an estimated 11.1m cases of measles would result over 25 years, according to their study in JAMA.
Measles has not been endemic in the United States since 2000, reports Reuters.
With vaccination rates dropping for MMR shots as well as for other childhood vaccines, outbreaks of preventable infectious diseases are increasing. There have been 10 reported outbreaks and at least 800 measles cases so far this year, including 624 cases and two deaths in one Texas outbreak, according to the Centres for Disease Control and Prevention (CDC).
Total US measles cases until 17 April represent about a 180% increase over the 285 cases reported in all of 2024 – the second highest annual case count in 25 years in the country, the CDC said.
The cases in the ongoing outbreak in Texas, New Mexico and Oklahoma have occurred among close-knit communities with low vaccination rates, according to the report. Overall, 96% of cases were in people who were unvaccinated or had unknown vaccination status.
Many state and national policies are being debated that may substantially reduce childhood vaccination even further, said Nathan Lo of Stanford Medical School who led the JAMA study.
The decline in vaccination among the nation’s children in recent years has been fuelled by promotion of theories – contrary to scientific evidence – that childhood vaccines are a cause of autism and other health risks.
Drawing on vaccination, birth and death data and historical data on measles infections, researchers simulated a population that mirrors the US population at national and state levels. Then they estimated how measles would spread under various scenarios if imported from a travelling American who gets infected abroad.
If routine childhood vaccinations declined by 50%, the country would see 51.2m measles cases, 9.9m rubella cases, and 4.3m poliomyelitis cases over the next 25 years, Lo said.
Under this scenario, there would be 51 200 patients with lasting neurologic side effects of measles, 10 700 birth defects resulting from congenital rubella infections, 5 400 cases of paralysis from polio, 10.3m hospitalisations, and 159 200 deaths.
Small increases in vaccination rates of around 5% could keep measles from becoming endemic, the researchers’ models suggest.
Troubling trend
Under current levels of vaccination, vaccine-preventable diseases other than measles are unlikely to become endemic, Lo said. But if vaccination rates drop by 35%, rubella may become endemic, while polio, which has long been eradicated in the US, has a 50-50 chance of making a comeback if vaccination drops by 40%.
No one can forecast exact vaccination and infection numbers, but the precise numbers don’t matter, said Dr Mujeeb Basit, associate director of the Clinical Informatics Centre at UT Southwestern Medical Centre, who was not involved in the research.
What matters, Basit said, was the trend revealed by the study: as the vaccination rate declines, the rate of increase in measles cases speeds up.
“If vaccination rates go 5% lower, you’ll have tens of thousands of infected patients,” he said.
“Rates just have to be 15% less and you’re at millions of cases,” he added. “The trend is what people need to know.”
Study details
Modelling Re-emergence of Vaccine-Eliminated Infectious Diseases Under Declining Vaccination in the US
Mathew Kiang, Kate Bubar, Yvonne Maldonado et al.
Published in JAMA on 24 April 2025
Abstract
Importance
Widespread childhood vaccination has eliminated many infectious diseases in the US. However, vaccination rates are declining, and there are ongoing policy debates to reduce the childhood vaccine schedule, which may risk re-emergence of previously eliminated infectious diseases.
Objective
To estimate the number of cases and complications in the US under scenarios of declining childhood vaccination for measles, rubella, poliomyelitis, and diphtheria.
Design, Setting, and Participants
A simulation model was used to assess the importation and dynamic spread of vaccine-preventable infectious diseases across 50 US states and the District of Columbia. The model was parameterized with data on area-specific estimates for demography, population immunity, and infectious disease importation risk. The model evaluated scenarios with different vaccination rates over a 25-year period. Inputs for current childhood vaccination rates were based on 2004-2023 data.
Main Outcomes and Measures
The primary outcomes were estimated cases of measles, rubella, poliomyelitis, and diphtheria in the US. The secondary outcomes were estimated rates of infection-related complications (post-measles neurological sequelae, congenital rubella syndrome, paralytic poliomyelitis, hospitalization, and death) and the probability and timing for an infection to re-establish endemicity.
Results
At current state-level vaccination rates, the simulation model predicts measles may re-establish endemicity (83% of simulations; mean time of 20.9 years) with an estimated 851 300 cases (95% uncertainty interval [UI], 381 300 to 1.3 million cases) over 25 years. Under a scenario with a 10% decline in measles-mumps-rubella (MMR) vaccination, the model estimates 11.1 million (95% UI, 10.1-12.1 million) cases of measles over 25 years, whereas the model estimates only 5800 cases (95% UI, 3100-19 400 cases) with a 5% increase in MMR vaccination. Other vaccine-preventable diseases are unlikely to reestablish endemicity under current levels of vaccination. If routine childhood vaccination declined by 50%, the model predicts 51.2 million (95% UI, 49.7-52.5 million) cases of measles over a 25-year period, 9.9 million (95% UI, 6.4-13.0 million) cases of rubella, 4.3 million cases (95% UI, 4 cases to 21.5 million cases) of poliomyelitis, and 197 cases (95% UI, 1-1000 cases) of diphtheria. Under this scenario, the model predicts 51 200 cases (95% UI, 49 600-52 600 cases) with post-measles neurological sequelae, 10 700 cases (95% UI, 6700-14 600 cases) of congenital rubella syndrome, 5400 cases (95% UI, 0-26 300 cases) of paralytic poliomyelitis, 10.3 million hospitalisations (95% UI, 9.9-10.5 million hospitalisations), and 159 200 deaths (95% UI, 151 200-164 700 deaths). In this scenario, measles became endemic at 4.9 years (95% UI, 4.3-5.6 years) and rubella became endemic at 18.1 years (95% UI, 17.0-19.6 years), whereas poliovirus returned to endemic levels in about half of simulations (56%) at an estimated 19.6 years (95% UI, 14.0-24.7 years). There was large variation across the US population.
Conclusions and Relevance
Based on estimates from this modelling study, declining childhood vaccination rates will increase the frequency and size of outbreaks of previously eliminated vaccine-preventable infections, eventually leading to their return to endemic levels. The timing and critical threshold for returning to endemicity will differ substantially by disease, with measles likely to be the first to return to endemic levels and may occur even under current vaccination levels without improved vaccine coverage and public health response. These findings support the need to continue routine childhood vaccination at high coverage to prevent resurgence of vaccine-preventable infectious diseases in the US.
Reuters article – US at tipping point for return of endemic measles (Open access)
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