Measles: Harbinger of Herd Immunity Concerns

Connecticut in relatively good position to fight off resurgence, says UConn Health expert

A hand clad in blue surgical glove holds a syringe and vial of MMR vaccine.

(Adobe Stock)

With measles on the rise worldwide and multiple states in the U.S. reporting cases, a real-life illustration of the effectiveness of childhood vaccinations is unfolding.

And it’s why Connecticut is in better position than most states to avoid an outbreak, according to a UConn Health and Connecticut Children’s pediatric infectious diseases expert.

One of the world’s most contagious diseases, measles was declared eliminated from the U.S. by the Centers for Disease Control and Prevention in 2000.

Dr. Melissa Held portrait white coat
Dr. Melissa Held is a professor of pediatric infectious diseases and the senior associate dean of medical student education at the UConn School of Medicine. (Tina Encarnacion/UConn Health photo)

“Measles was not eradicated, but under very good control in many regions in the world due to the success of various vaccination campaigns,” says Dr. Melissa Held, professor of pediatric infectious diseases at the UConn School of Medicine. “We are hearing about it again because of various factors, including suboptimal vaccine coverage, vaccine hesitancy, international travel, and importation of the virus.”

Held says an increase in measles usually occurs because of an increase in the number of travelers who get measles abroad and bring it into the U.S. and/or spread within the U.S. in communities where there are pockets of unvaccinated people. But the recent cases in our country are concerning given more widespread outbreaks globally.

Another reason for concern is the decline in the rate of young children completing their recommended vaccination schedules since the pandemic, which Held says has led to communities falling short of the herd immunity target vaccination level of 95%.

“High vaccine coverage in populations is essential for achieving herd immunity, which protects individuals who cannot be vaccinated because of medical or health reasons or because of young age,” Held says. “Vaccinations not only protect your child or yourself from these diseases, but they also protect those around you who are not yet old enough to receive the vaccines (infants) or those with impaired immunity.”

The measles-mumps-rubella (MMR) vaccine delivers immunity from measles at a rate of nearly 93% after one dose (usually around age 12 to 15 months) and 97% after a booster usually taken between ages 4 and 6.

Vaccines are probably the most significant modern medical miracle of our time.
— Dr. Melissa Held

The World Health Organization says because of its high transmissibility, measles can serve as an early warning system by exposing immunity gaps in a population.

The latest available data on vaccination rates in Connecticut show ours among the leading states, with more than 97% of kindergarteners having received the required MMR vaccines in the 2022-23 school year.

“Connecticut tends to do much better than the rest of the country, not just with the MMR vaccine but with all other vaccines as well,” Held says. “Unfortunately, the national average of coverage is lower than the ideal 95% threshold, so there are many states with increased risk of outbreaks.”

See the CDC’s current recommendations on child and adolescent immunizations.

Held, who is UConn’s senior associate dean of medical student education and also sees hospitalized patients at Connecticut Children’s, recommends parents who are hesitant to follow the recommended vaccination schedule for their children share their concerns with their pediatrician and try to tune out the noise.

“Look to reputable source of information like CDC, World Health Organization and the American Academy of Pediatrics; the internet is full of misinformation and random opinions that are not scientifically sound,” Held says. “Vaccines are probably the most significant modern medical miracle of our time. The reason we do not worry about our children and family members becoming sick or dying from these diseases is because we have such effective vaccines.”