Outbreaks of measles have affected parts of the United States, coinciding with the lowest child immunisation rates the country has seen in 10 years, according to a report from the Centers for Disease Control and Prevention (CDC).

By 22 February, 35 measles cases had been reported by 15 states, namely Arizona, California, Florida, Georgia, Indiana, Louisiana, Maryland, Minnesota, Missouri, New Jersey, New York City, Ohio, Pennsylvania, Virginia, and Washington, according to the CDC.

However, unlike other parts of the world where measles is rife because immunisation programmes have been disrupted by conflict or weak health systems, the drop in child immunisation in the US is parent-driven. 

In 2023, the highest number of parents filed for their children to be exempted from school vaccination requirements. Immunisation with the measles, mumps, and rubella vaccine (MMR) dropped in 29 states in 2023, while exemptions increased in 40 states and DC, with 10 states reporting an exemption from at least one vaccine for more than 5% of kindergartners, according to the CDC.

The CDC reported that its childhood immunisation rate for all three required childhood vaccines – MMR, polio and diphtheria, tetanus, and acellular pertussis vaccine (DTaP) – is 93%, whereas the threshold for herd immunity is generally regarded as 95%. 

“National MMR coverage among kindergarten students remained below the Healthy People 2030 target of 95% for the third consecutive year,” according to the CDC. Idaho reported the lowest rate (81.3%) and Mississippi, the highest (98%).

“National MMR coverage of 93.1% during the 2022–23 school year translates to approximately 250,000 kindergartners who are at risk for measles infection.”

Most contagious disease

Measles is one of the world’s most contagious diseases, spread by droplets from infected people coughing or sneezing.

“The virus remains active and contagious in the air or on infected surfaces for up to two hours. For this reason, it is very infectious, and one person infected by measles can infect nine out of 10 of their unvaccinated close contacts,” according to the World Health Organization (WHO).

Most deaths from measles are from complications related to the disease, including encephalitis, severe diarrhoea and pneumonia.

It also has a long incubation period, which is why there has been controversy over Florida’s Surgeon General Dr Joseph Ladapo’s decision to allow the parents of unvaccinated children to ignore the CDC’s advice that they should quarantine for 21 days.

Europe has also seen an increase in cases: “Last year, more than 58 000 people in 41 of the 53 member states in the region – straddling Europe and central Asia – were infected with measles, resulting in thousands of hospitalisations and 10 measles-related deaths,” according to WHO Europe.

“The high proportion (nearly half) of cases among children below five years of age reflects, once again, the enormous impact of the COVID-19 pandemic on health systems, including routine immunisation services. This has resulted in a significant accumulation of susceptible children who have missed their routine vaccinations against measles and other vaccine-preventable diseases.”

“Vaccination is the only way to protect children from this potentially dangerous disease. Urgent vaccination efforts are needed to halt transmission and prevent further spread,” explained Dr Hans Henri P.Kluge, WHO Regional Director for Europe.

Image Credits: WHO.