Measles Outbreak in the US: Rising Vaccine Hesitancy at the Core

The United States is grappling with a rise in measles cases. According to the US Centers for Disease Control (CDC), the incidence of measles has seen a significant spike in 2025. As of March 28, 2025, as many as 483 cases have been reported across 20 states, compared to 285 cases in 33 states for the entire year of 2024.

Among the 50 states, Texas is the hardest hit, with 400 cases identified since late January. As many as 41 patients have been hospitalized, according to the Texas Department of State Health Services.

The Texas Health Authority also reported one fatality: a school-aged child from the outbreak area. "The child was not vaccinated and had no known underlying conditions," the department said in a statement issued on March 25.

This deadly outbreak could result in the US losing its measles elimination status. It is important to note that the US had declared measles eliminated in 2000, meaning there was no continuous transmission of the disease in the country.

Cause of the Outbreak

The obvious question is why the US is seeing a spike in measles cases now. According to health officials, the rise in vaccine hesitancy is a significant factor.

The CDC reported that kindergarten measles-mumps-rubella (MMR) vaccine coverage dropped from 95.2% during the 2019-2020 school year to 92.7% in 2023-2024, "leaving about 280,000 children at risk."

The New Jersey Department of Health also observed that "95% of the cases reported in the United States for 2025 are among children and individuals who had not received the MMR vaccine or have unknown vaccination status."

How Measles Transmits

Before understanding why parents have been sceptical about the MMR vaccine, let’s look at how measles spreads.

Measles is a highly contagious acute viral respiratory infection and a major cause of mortality and morbidity, particularly among children under five years of age. In severe cases, it can lead to complications such as pneumonia, encephalitis, diarrhoea, dehydration, ear infections, and irreversible vision loss. Infants and young children who are malnourished or have compromised immune systems are especially vulnerable to these complications.

Measles is primarily transmitted through large respiratory droplets via coughing and/or sneezing or through aerosolized particles that remain airborne for up to two hours in enclosed spaces.

Some early symptoms include fever, accompanied by cough, coryza, and conjunctivitis.

Given the continued viral shedding from the infected individual, measles can be transmitted four days before and four days after the appearance of a maculopapular rash – a skin eruption characterized by flat, discoloured patches and small, raised bumps.

According to a report published in the National Library of Medicine, more than 90% of susceptible individuals in the vicinity of an infected person will develop measles.

Reasons for Vaccine Hesitancy

According to the same study mentioned above, fear of autism was the most commonly cited reason for hesitancy toward the MMR vaccine. “Vaccine hesitancy toward MMR and other childhood vaccines was found to be prevalent in middle- to high-income areas among mothers with a college-level education or higher who preferred internet or social media narratives over physician-based vaccine information,” the study stated.

The research also highlighted low parental trust, low perceived disease susceptibility, and scepticism about vaccine safety and benefits.

Prior to the introduction of the MMR vaccine, the US experienced almost four million cases of measles annually, resulting in 400 to 500 deaths and 48,000 hospitalizations.

After the rollout of the MMR combination vaccine, measles cases in the US plummeted by more than 99%, leading to its subsequent elimination in 2000. To maintain herd immunity, the Centers for Disease Control and Prevention (CDC) recommends a 95% or higher immunization coverage with a two-dose MMR series, administered at 12–15 months and again at 4–6 years of age.

However, over the years, vaccination rates have dropped, leaving many susceptible to the deadly disease.

According to the study, from 2000 to 2017, global coverage rates for the first and second doses of the measles vaccine stalled at 85% and 67%, respectively, instead of the 95% target needed to prevent outbreaks. Complacency in preventing transmission of the disease led to a 31% global increase in cases in the Americas, East Mediterranean Region, and Europe in 2016-2017.

The COVID-19 pandemic further aggravated the situation, disrupting vaccination routines.

According to a recent study by Benjamin Rader, a computational epidemiologist at Boston Children’s Hospital, approximately 20,000 parents of children under 5 were surveyed from July 2023 to April 2024. It was found that only 71.8% reported that their children had received at least one dose of the MMR vaccine, much lower than the CDC’s estimates.

The study was published online in February in the American Journal of Public Health.