The diseases are highly contagious, but they are also preventable; two of the many recommended childhood vaccinations protect against measles and pertussis. And measles had been considered effectively eliminated in the United States. What's going on, exactly? Here are some answers.
Why are so many outbreaks happening? Although it's a complex problem, health officials say one key culprit is that more and more people are choosing not to get their kids vaccinated against these diseases. For instance, in California parents are increasingly seeking personal or religious exemptions from vaccination requirements for their kids to attend schools. Substandard vaccination rates create an opening for outbreaks, which often start when an unvaccinated person catches the disease while traveling abroad and spreads the illness to friends and family upon returning.
But aren't overall vaccination rates really high? Nationally, yes, though it wasn't always this way. Before the 1990s, rates languished below 80 percent for most childhood vaccines at the time. In 1993, after the 1989-1991 measles outbreak, Congress enacted the Vaccines for Children (VFC) program to promote childhood vaccinations.
CDC data show that vaccination rates are now above 90 percent range for several routine vaccines, including the measles-mumps-rubella (MMR) and whooping cough vaccines. Public health officials target a 90 percent vaccination rate for most routine childhood vaccines. Experts say that a population has "herd immunity" when enough people are vaccinated to prevent a disease from taking hold. This chart shows how vaccination rates climbed after VFC's enactment:
If vaccination rates are high, why are we seeing so many outbreaks? That's because vaccination rates aren't geographically uniform. Public-health experts say that high non-vaccination or exemption rates can occur among pockets of people, particularly at the county or city level. And some research has found that outbreaks are far more likely to happen in these areas, such as during the recent whooping cough outbreaks in California.
Why are people not vaccinating their kids? There are a number of factors at play. Many of the diseases we vaccinate against are so rare here now that the public's awareness of vaccination might have decreased. But the one reason that has most alarmed public-health experts lately has been the rise of the anti-vaccine movement. Groups and activists such as celebrity Jenny McCarthy have repeatedly claimed that vaccines cause autism. This vaccine-autism concern may be causing a drop in childhood vaccination rates in many communities, including in affluent, well-educated ones.
Do vaccines cause autism? Science gives a resounding no. Anti-vaccine activists often hang their case on a study published in the British journal The Lancet in 1998. This study, which posited a link between the MMR vaccine and autism, was widely discredited by the scientific community and eventually retracted. But the anti-vaccine movement has still gained steam.
Anti-vaccine activists have also raised concerns about vaccines made with the mercury-based preservative known as thimerosal, which they worry could cause brain damage in developing kids. It's true that vaccines once routinely contained thimerosal, which government officials recognized as generally safe. But this preservative has been phased out of nearly all vaccines as a precautionary measure.
Anti-vaccine activists also worry that the CDC's recommended vaccination schedule could overwhelm infants' immune systems by packing too many doses into a short period of time. Although the number of vaccinations that kids receive now is higher than it used to be, the main ingredients in the vaccines have actually decreased in amount. Even if these ingredient amounts hadn't decreased, research has found no relationship between those amounts and autism risk.
Vaccines do carry a risk of side effects, but they are usually minor. The CDC has concluded from reviewing the scientific evidence that there's no causal link between childhood vaccinations and autism.
Routine vaccines save lives, says science. A new study from CDC researchers led by Anne Schuchat analyzed what happened to disease rates as childhood vaccination rates increased starting in the early 1990s. The researchers used these findings to model the resulting effect over the kids' lifetimes. In the analysis, the researchers factored in most routine vaccines recommended for children below age 6 (among them the MMR and whooping cough vaccines). Their findings: Routine childhood vaccinations given between 1994 and 2013 will save 732,000 lives and prevent 322 million cases of illness and 21 million hospitalizations over the course of the children's lifetimes.
Vaccines provide high public-health bang for the buck. The CDC researchers also weighed the benefits of the vaccinations ("savings in direct and indirect costs that accrued from averting illnesses, hospitalizations, and deaths") against costs ("program costs included vaccine, administration, vaccine adverse events, and parent travel and work time lost"). In 2009 alone, the researchers determined, each $1 spent on vaccines and their administration yielded $10 in benefits to society. And the vaccinations from 1994-2013, the researchers found, will save society a net $1.38 trillion, both directly (by reducing health expenses) and indirectly (via the economic activity that is saved from avoided illnesses). That's almost 10 percent of the U.S. economy's gross domestic product.
The CDC study may actually underestimate some benefits. Here's why. It doesn't account for cost savings to society brought on by preventing the diseases' spread to unvaccinated populations, "a powerful driver of cost-effectiveness" in the researchers' view. The study also excludes the influenza and hepatitis A vaccines, and thus fails to capture their benefits.
What's the bottom line? Vaccines may not be perfect. But the science suggests that they are effective -- especially when enough people are receiving them -- and there's still no evidence that they cause autism.