Where states stand on vaccinations

In the 2013-2014 school year, 94.7% of kindergartens received both doses of the measles, mumps, and rubella (MMR) vaccine, according to CDC data. But at the community level, where herd immunity really matters, vaccination rates vary significantly.

Altogether, 17 states have MMR vaccination rates below 90% among preschoolers. The five states with the lowest vaccination rates are:

• West Virginia (86%);
• Ohio (86%);
• Colorado (86%);
• Montana (87%); and
• Louisiana (88%).

All five states—and more than a dozen others—fall well below the vaccination rate that CDC says is needed to maintain herd immunity against measles, about 92% and 95%.

Moreover, rates can vary within a state, with specific communities reporting significantly lower rates. A USA Today analysis of vaccine data from 13 states found that nearly one in seven schools have MMR immunization rates below 90%. At some schools, the rate falls below 50%. "Really, what should concern parents is the microclimate of their child's school or day care center," says Sunari Kraft, who helped pass a bill last year requiring Colorado schools to provide vaccination data on request.

The issue, experts say, is in state policies.

Every U.S. state requires children to receive the MMR vaccine. But data compiled by the Immunization Action Coalition (IAC), which is funded in part by CDC, show that only two states have limited vaccine exemptions for the MMR vaccine to medical reasons: Mississippi and West Virginia. Most states also allow exemptions for religious or personal reasons—or both.

Evidence suggests that parents are taking advantage of these exemption options. In five states, more than 5% of kindergartens were exempt from vaccinations for nonmedical reasons during the 2013-2014 school year: Idaho, Maine, Michigan, Oregon, and Vermont.

According to IAC, these exemptions can be directly linked to outbreaks. In a research review, the group said, "Several recent outbreaks of measles, pertussis, and varicella (chickenpox) have been traced to pockets of unvaccinated children in states that allow personal belief exemptions."

Or, as one New York Times blogger puts it, "A strict vaccine requirement—without loopholes—is all it would take to reduce the numbers of unvaccinated children to levels that would allow us to maximize protection for everyone."

Will more states tighten their rules?

Thrust in the national spotlight, state vaccine rules are getting new scrutiny. Earlier this week, top Republican legislators offered strong support for routine vaccinations, in what the Wall Street Journal considers a "shift in the political debate" around immunization policies.

It's unlikely that we will see a new federal policy on vaccines. "I don’t know that we need another law, but I do believe all children ought to be vaccinated," House Speaker John Boehner (R-Ohio) says.

But at the state level, some politicians are trying to take action. In California, lawmakers have introduced legislation tightening vaccination rules, which have been notoriously lax in recent years and lead to pockets of unvaccinated Americans.

New York does a better job of vaccinating kids than L.A. Here's why.

That said, states are not all thinking about moving in the same direction. In New York State, legislators are considering a bill that would make it easier for parents to exempt their child from vaccine requirements.