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Slowing pertussis with ‘herd immunity’

It takes a herd to whip whooping cough.

“Herd immunity” is the idea that people who can’t get immunized for medical reasons – such as autoimmune disorders – or because they’re too young are still protected indirectly from infectious diseases. That’s because they’re surrounded by people who are immunized.

Depending on the illness, a certain percentage of the community has to be vaccinated to achieve herd, or community, immunity. For the flu, it’s around 50 percent, said Kristi Siahaya, an immunization outreach specialist with the Spokane Regional Health District.

For pertussis, it’s more than 90 percent, she said.

As of April, about 81 percent of children in Spokane County had at least one dose of vaccine, of the five total recommended for children.

About 22 percent of people ages 7 to 65 had received the single booster shot recommended by health officials.

In Spokane County, more parents are receiving vaccine exemptions for their children, meaning they’re legally excused from being immunized because of personal or religious beliefs or medical reasons, Siahaya said.

In the 2010-’11 school year, about 6.4 percent of Spokane County kids from kindergarten through 12th grade were exempt, according to data from the state Department of Health. The vast majority of those were for “personal” reasons. In 2000-’01, the rate was 4.3 percent, and it had been inching up for at least a couple of years.

For many, the reluctance to immunize – children especially – stems from a belief that any risk associated with a vaccine is greater than the risk of the disease, Siahaya said.

“There’s this sense of guilt, that if (parents) choose to get their kid a vaccine and something happens, then it’s their fault,” she said. “But they don’t feel like it’s their fault if they don’t get the vaccine and they get the disease.”

A study linking childhood vaccinations and autism has been discredited – called an “elaborate fraud” by one medical journal – and researchers have been able to find no connections between the two. But that study’s effects on worried parents linger.

And, as with all vaccinations, there are real risks associated with the pertussis vaccine. They include a small risk of an allergic reaction, fainting spells or seizures.

But “for the most part, honestly, the side effects that happen the most are a sore arm, redness at the injection site – that’s about it,” Siahaya said.

Other parents note that vaccines cover illnesses we rarely see in the U.S., such as polio or rotavirus, and worry a vaccine puts their child at needless risk. But it’s because we vaccinate that we don’t see those illnesses, Siahaya said – they’re still rampant in countries that lack strong immunization programs.

“It’s just a bombshell waiting to happen if we don’t vaccinate here,” Siahaya said. “It’s still out there in the world.”