If immunizing children were a team sport, Washington state would get the “most improved player” award.

In health care as in sports, though, recognition like that tends to follow a record of underperformance.

So while Washington improved its score on the National Immunization Survey more than any other state (from a vaccination rate of 56.2 percent in 2003 to 71.2 percent in 2006), we began so far back in the pack that we still fall short of the state and national goals of 80 percent.

One reason for this shows up in another category in which Washington leads the nation: The percentage of children whose parents sign a waiver excusing them from vaccinations required for school enrollment. Washington’s waiver rate – 6 percent – is among the highest in the nation.

State lawmakers are partly at fault for that dubious standing. Public health officials rank Washington’s process for granting waivers as the most lenient in the country. A parent’s signature is all it takes for a child to enroll in school without the battery of shots other children receive to protect them – and those with whom they’re in contact – from 18 serious but preventable diseases.

No explanation is required. No declaration of religious or philosophical principle is needed. No health concern must be attested to by a physician. Just a signature.

Perhaps the parent has read a scare story on the Web. Perhaps family legend includes the suspicious death of a child in a previous generation. Maybe it’s just too traumatic to subject one’s frightened youngster to the unpleasantness of a needle poke, regardless of the benefits to be achieved. Or maybe the parent is just feeling a little contrary that day (officials report that some families execute the waiver even though their children already have received some immunizations).

There are reasons, including religious or philosophical grounds, that a free society should respect regarding mandatory health care actions. Most if not all states waive vaccination requirements under certain conditions. But it’s not too much to expect, given the implications, that parents should have to spell out their reasons.

Unvaccinated children share diseases with classmates, playmates and neighbors – even aging grandparents and great-grandparents, who, like infants, can be particularly vulnerable to infection.

Dr. Anne Schuchat, who heads the immunization program for the Centers for Disease Control and Prevention, says that by the time a nationwide generation of kids reaches 18, immunizations spare them 14 million infections and 33,000 deaths, while saving the health system $43 billion.

Still, some families will weigh those outcomes against religious convictions or speculation about unproven links between vaccination and autism; that is their right. But the overwhelming evidence about the benefits of immunization imposes a burden on them to explain why. Washington lawmakers should address that.