The measles outbreak that began at the Disneyland theme parks in Anaheim has reminded us of the importance of herd immunity. A quick refresher: When more than 92 percent of a given population is vaccinated against measles, we say a community has herd immunity.
Herd immunity creates a type of protective wall, shielding those who can't get vaccinated from the contagious disease.
Check out how I explained it on the radio (thanks to freeSFX for sound effects):
Among those relying on this wall of immunity is 4-year-old Brooklyn Roffman of Altadena.
Brooklyn is one of those vulnerable children who can't get vaccinated for medical reasons. In Los Angeles County, 169 kids entered kindergarten this school year with a Permanent Medical Exemption, which means they can't get one or more vaccines.
When I met her last week in Altadena, she requested that her mom, Sandy Roffman, call her "Minnie," a reference to the pink mouse ears the little girl wore on her head. The headband pushed back her wispy curls, which have grown back after more than two years of chemotherapy.
Compromised immune system
Brooklyn has acute lymphoblastic leukemia. She was diagnosed with the childhood cancer more than two years ago. In fact, her diagnosis came just 10 days after her younger sister, Indie, was born eight weeks early.
"Your first thought is, 'My kid has cancer,'" Roffman says. "But the cancer is the least of your concerns, because the complications are the worst part by far."
Brooklyn's immune system was wiped out after she started chemotherapy in January 2013. Her mom, Sandy Roffman, recalls the precautions she and her husband had to take to protect the two children, both of whom are immunocompromised.
"My husband and I both work in television, so you're on these big, filthy film sets all day long," Roffman says. "He would come home from work, he would change his clothes, and he would scrub down."
"If people came in, I would have to mop when they left," she says. "I requested everybody sanitize their hands."
Especially during the first six months of Brooklyn's illness, Roffman would avoid taking Brooklyn out of the house. But when she had to leave the house – say, for one of Indie's well-child visits — Roffman would do her best to protect Brooklyn.
She'd put a mask on her daughter's face, and "I would have to keep her swathed in a blanket in a stroller, keep the stroller covered up," she says, adding, "That's really hard to do when you have a 3-year-old who wants to touch everything and see everything."
Brooklyn has been in "technical remission" — meaning there's no longer cancer in her bone marrow — for just under two years. Still, Roffman is very cautious: Just last week, she took Brooklyn to the hospital for a runny nose. She made her daughter wear a mask all day, noting that she can't be too careful, especially during cold and flu season.
Despite all of this, Brooklyn has gotten sick.
Roffman says the family spent all of last March in the hospital because Brooklyn had caught a cold.
"If the common cold is going to put you in the hospital for a month, something like measles – that's an end game," she says.
That's why she's so nervous about the measles outbreak that's infected more than 100 Californians and others since late December.
"You don’t go two and a half years, through all this stuff, and get nailed by measles at the end of it all," Roffman adds.
Brooklyn underwent her final chemotherapy treatment last week. If an April checkup determines that she's in full remission, then after another six months she will be able to join the ranks of the vaccinated — something her mother says she'll take care of as soon as she can.
In the meantime, Sandy Roffman must rely on other parents to vaccinate their kids to shield Brooklyn from measles and other contagious diseases.
And that's proving difficult.
Brooklyn is supposed to enter kindergarten in the fall. But the best school for her aptitude might not be the best one for her health: At one school Roffman checked out, almost 14 percent of last fall's incoming kindergartners were unvaccinated, due to their parents' personal beliefs.
That's below the level needed to achieve herd immunity, making it more likely that measles could spread throughout the school.
Dr. Walt Orenstein, a professor of medicine and pediatrics at Emory University and associate director of the Emory Vaccine Center, says it's critical to maintain herd immunity levels within small communities – like schools, workplaces and religious communities.
"Even if you have a high level of immunity in your state, if you have substantial sub-populations with low immunity, you can get sustained transmission" of infectious diseases, he says.
Two years ago, with the support of the Make-a-Wish Foundation, Brooklyn and her family went to Disneyland, where this most recent measles outbreak began.
If she could make another wish today, Sandy Roffman says it would be that all parents vaccinate their kids to protect those who can't get vaccinated.
Regarding those parents who don't vaccinate their children due to personal beliefs, she says: "They don't think as far as someone in Brooklyn's situation, and there are a lot of kids out there right now who are very, very sick."
"To deliberately not vaccinate your child, and then expose them to the rest of the world, ... you're playing with fire at that point," Roffman adds.