Measles Vaccination Rates May Be Lower Than Thought

Measles vaccination rates for young children may be far lower than publicly reported, a troubling development that could mean the United States is closer than expected to losing its “elimination status” for the extremely contagious disease.

Introduction to the Concern

“We are experiencing an extremely concerning decline in measles vaccination in the very group most vulnerable to the disease,” said Benjamin Rader, a computational epidemiologist at Boston Children’s Hospital, an assistant professor at Harvard Medical School and the author of a recent study that looked at children’s vaccination rates.

As of Wednesday, there have been over 420 cases of measles this year – already surpassing the total number of cases for 2024. Most are in West Texas, where a growing outbreak has spread into neighboring states, but a handful of cases, linked to international travel, have been reported in other states. The cases have mostly been in unvaccinated people or those with an unknown vaccination status, according to the Centers for Disease Control and Prevention.

Measles is a highly contagious airborne disease caused by a virus that can lead to severe complications and death. Measles is one of the most contagious viruses in the world, so pockets of under-vaccinated areas can make it easier to gain a foothold and spread, Rader said.

Sampling Bias in Vaccination Data

The CDC recommends two doses of MMR vaccine to protect against measles, mumps and rubella, first at ages 12 to 15 months and the second shot at ages 4 to 6 years before entering school. The agency estimates 92.7% of kindergarteners have had two doses of the vaccine. That’s not high enough, said Dr. Brian Clista, a pediatrician who works in private practice in Pittsburgh.

“The 92% vaccination status reported by the CDC is still below the recommended rate of 95% to produce herd immunity — so it’s not where we need to be,” Clista said. However, Rader said that the true MMR vaccination rate among young children can be misrepresented by publicly reported numbers, because MMR surveillance is drawn from older children who are already in kindergarten.

Younger children under the age of 5 are not fully captured in surveillance data because they have not reached kindergarten age — although a 2021 estimate from the CDC notes a subset of younger children, namely those who received at least one MMR dose by 24 months, were 90.6% vaccinated for measles.

In Rader’s study, published online in February in the American Journal of Public Health, his team surveyed approximately 20,000 parents of children under 5 from July 2023 through April 2024, finding only 71.8% reported that their children received at least 1 dose of MMR vaccine — much lower than CDC estimates.

The researchers used a digital surveillance platform that the CDC has used to estimate things like at-home Covid testing, he said. Rader downplayed the difference in numbers between his findings and the CDC data, emphasizing that, while accurate, the CDC data does not provide a complete picture — despite its best intentions.

The Pandemic Exacerbated Vaccine Hesitancy

The pandemic disrupted health care access, which made it harder for people to get routine care and increased vaccine hesitancy over the Covid vaccine, which also spilled over and affected MMR vaccine rates, Rader said. The study found 20% more children were vaccinated for measles when their parents were vaccinated for Covid.

“Unfortunately, routine vaccination is trending substantially lower, although there is the hope that it will catch up,” Rader said. Katherine Wells, director of public health for Lubbock — the largest city in West Texas, where the current outbreak is centered — said school enrollment requirements should help many children catch up as they enter pre-K or kindergarten.

Heading Towards Losing Elimination Status

Measles has been “eliminated” in the U.S. since 2000 — meaning that the country hasn’t had a chain of transmission extend for more than 52 weeks. “With the absence of sustained measles virus transmission for 12 consecutive months in the presence of a well-performing surveillance system, the United States has maintained measles elimination status since 2000,” a CDC spokesperson told NBC News.

“This temporal boundary, however, was nearly breached in 2019,” said Dr. Jonathan Temte, professor of family medicine and community health at the University of Wisconsin School of Medicine and Public Health. Temte was part of the team that declared measles eliminated in 2000. When he served on a panel to recertify measles elimination in 2011-12, one of his greatest concerns, he said, was the rising rates of vaccine exemptions among children and the cases brought into the U.S. after international travel that could lead to endemic transmission.

Now additional factors might be creating a perfect storm for the U.S. to lose its elimination status, including declining vaccination rates, increasing pockets of unvaccinated individuals and greater ease in travel. Measles is also contagious before its characteristic rash appears, often creating a delay in diagnosis and allowing it to spread before people know they are infected.

Conclusion

The potential for the U.S. to lose its measles elimination status is a serious concern, driven by declining vaccination rates among young children and the challenges posed by the pandemic. Experts emphasize the need for increased vaccination efforts and awareness about the risks of measles to prevent the spread of the disease and maintain public health.

FAQs

• Q: What is the current measles vaccination rate among young children in the U.S.?
  A: The study found that only 71.8% of children under 5 have received at least one dose of the MMR vaccine, which is lower than the CDC’s estimate of 92.7% for kindergarteners.
• Q: Why are measles vaccination rates lower than reported?
  A: The true vaccination rate may be misrepresented due to sampling bias, as MMR surveillance data is drawn from older children who are already in kindergarten, leaving younger children under 5 underrepresented.
• Q: What factors contribute to the decline in measles vaccination rates?
  A: Factors include the pandemic disrupting healthcare access, increasing vaccine hesitancy, and a growing number of parents opting out of vaccinations.
• Q: What are the implications of the U.S. losing its measles elimination status?
  A: Losing elimination status means the country would have sustained measles transmission for more than 52 weeks, indicating a significant public health failure and increased risk of outbreaks.
• Q: How can the spread of measles be prevented?
  A: Preventing the spread of measles requires maintaining high vaccination rates, especially among young children, and addressing vaccine hesitancy through education and access to healthcare.