Childhood Diseases

19 June 2015

Worrying dip in US child vaccinations

When vaccination rates go down, 'herd' immunity also declines, according to experts.


Although most U.S. children are getting their routine vaccinations, recent trends have experts concerned that Americans will lose some of the "herd immunity" that has long protected many from serious infections.

Parents skip or delay vaccinations

The vast majority of U.S. kids are up-to-date with routine jabs against once-common infections like polio, measles, mumps, whooping cough and chickenpox. But that "coverage" varies from state to state, according to the latest figures from the U.S. Centres for Disease Control and Prevention.

In 2013, there were 17 states where less than 90 percent of 1.5- to 3-year-olds had gotten their first dose of the measles-mumps-rubella (MMR) vaccine, the CDC found.

And nationally, recent years have seen a small dip in the percentage of young children who are up-to-date with some other vaccines, according to Dr. Mark Sawyer, an infectious disease specialist at Rady Children's Hospital and the University of California, San Diego, School of Medicine.

Read: Initiative to study secrets of infectious diseases

It's concerning, Sawyer said, because some parents are opting to skip or delay vaccinations not for medical reasons, but for "personal beliefs" – mainly, unsupported fears about vaccine safety.

Normally, in a community where most people are immunised, the unvaccinated few are still protected by the cocoon of immune folks around them. That so-called herd immunity shields infants who are too young for certain vaccines, and people who can't be immunised because of a medical condition.

"But herd immunity is only as good as the herd you're in," said Sawyer, who spoke this week at a news conference sponsored by the March of Dimes.

"I'm concerned that we're slowly losing the battle, and we're about to lose some of this herd immunity," Sawyer said. "How about Disneyland and the measles outbreak as an example?"

He was referring to the measles outbreak that, as of May 29, has sickened 173 people in 21 U.S. states and Washington, D.C., according to the CDC. The main outbreak was traced to Disneyland, in California.

The CDC says it probably began with an unvaccinated traveler who became infected in another country before visiting the amusement park, where he or she encountered other unvaccinated people.

Worries about vaccine safety

"It's remarkable that this one case managed to spread to over 100 people," Sawyer said.

Some U.S. parents, he noted, think diseases like measles and whooping cough are relics of the past, so skipping or delaying their children's vaccinations will cause no harm. But unvaccinated, and unknowingly infected, travelers flow in and out of the United States all the time, Sawyer said – and those travelers are typically the "index case" in disease outbreaks here.

Read: Vaccine fears unfounded

"They're not from third world countries, either," Sawyer noted. "They're often from highly developed European countries where vaccination rates are low and they've let the genie out of the bottle."

What's more, parents' worries about vaccine safety have no science behind them, emphasized both Sawyer and the CDC's Dr. Sonja Rasmussen, who also spoke at the conference.

The notion that the MMR vaccine causes autism has lingered for years, even though the 1998 study that proposed the theory was later found to be fraudulent.

Another misperception, Sawyer said, is that the current vaccine schedule subjects babies and preschoolers to too many shots in a short period. As a result, some parents ask their doctors to delay certain vaccines – and, recent research shows, they often get their wish.

However, Sawyer said, studies have found no evidence that the vaccine schedule "overwhelms" babies' immune systems.

In contrast, no studies have looked at whether delayed or "alternative" vaccination schedules are as effective as the recommended one.

"The recommended schedule is not put together casually," Sawyer said. "There's a lot of science behind it."

Rasmussen underscored another strategy for protecting young infants: Vaccinating moms-to-be and family members.

Booster shot against whooping cough

Pregnant women should get a flu shot, she said, because it lowers their risk of a severe case of the flu, and the pregnancy complications that can cause. Plus, moms pass on some of those flu-fighting antibodies to their babies.

Read: Childhood vaccinations

That's important, Rasmussen said, because infants cannot get the flu vaccine until the age of 6 months.

Pregnant women should also get the Tdap booster shot against whooping cough, because immunity to that infection wanes over time, Rasmussen said. The same goes for family members and anyone caring for the baby, since infants do not get their first shot against whooping cough until they're 2 months old.

For adults and older kids, whooping cough is miserable but relatively mild. That's not true for infants, Rasmussen pointed out.

"It's babies who are at risk of severe infections and death," she said.

Sawyer stressed the point of community protection. High vaccination rates keep vulnerable groups, like infants without full immunity, safe from serious infections, he said.

"When you decide not to vaccinate your child," Sawyer said, "it affects the whole community."

Read more:

Parents still worried about vaccine safety

Autism/vaccine data faked: report

Vaccine breakthroughs

Image: Canned vaccination from Shutterstock

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Prof Eugene Weinberg worked in the Paediatrics Department of the Red Cross Children’s Hospital for many years. He is presently a paediatric allergist at the Allergy Diagnostic Unit of the UCT Lung Institute in Mowbray.

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