The United States this year is set to have the worst outbreak of whooping cough since the 1970s. From January to mid-July, there were 17,000 registered cases and nine deaths.

Like the whoop that punctuates the cough, this number is a warning that something is very wrong.

The increase, researchers suspect, is partly due to the waning effect of whooping cough vaccines introduced in the 1990s to replace older formulations. It’s also connected to the rising number of parents who refuse to get their children immunized because of a dangerously misinformed belief that vaccines are more harmful than the diseases they prevent.

The problem is illustrated by Washington state, ground zero of the outbreak. Overall, Washington has a good record of vaccinating kids for whooping cough, also called pertussis. Yet performance varies by community. In San Juan County, in the northwest of the state, only 52 percent of kindergartners and 4 percent of sixth-graders were up-to-date on their pertussis shots for the 2010-2011 school year. Not surprisingly, the incidence of the disease there is elevated.

This pattern is repeated across the country. Because the U.S. has made great strides in making vaccines available and inexpensive, immunization rates overall are at an all-time high. You might think this would create the herd immunity for which health workers aim: When a sufficient portion of a population (generally, 90 percent) is vaccinated, the pathogen can’t easily transmit in a community, so it dies off. What has happened, however, is that holes in the protective cover have opened as geographic clusters of parents, such as the one in San Juan County or another around Boulder, Colo., have rejected vaccines. These communities are disproportionately white, educated and well-off.

Their children are at much higher risk of illness; they are 35 times more likely to get measles, for instance. Once infected, they spread disease to others, including those who for medical reasons can’t be vaccinated, those for whom a given vaccine doesn’t work, and infants too young to be vaccinated. Babies account for most of the pertussis deaths this year.

Pertussis and measles are the first of the childhood diseases to make a comeback in the face of vaccination refusals, probably because they are especially contagious. Last year, the U.S. recorded 222 measles cases instead of the usual 60.

Since the early 1980s, every state has required children to be inoculated against childhood diseases before they are admitted to school, unless they have a medical exclusion. Forty-eight states allow religious exemptions as well and 20, philosophical ones. The use of these waivers has grown as more parents are fooled by overhyped, inaccurate reports of vaccine risks, most notoriously a bogus 1998 study — since retracted by its publisher — linking the mumps, measles and rubella vaccine to autism.

Some health experts have argued that states should abolish all but the medical waivers. After all, courts have consistently upheld vaccine mandates. Striking down a religious exemption, the Mississippi Supreme Court said the state had an “overriding and compelling public interest” to protect children, even when it conflicts with the religious rights of parents.

With more than half of parents expressing concern about vaccine safety in one survey, however, abolishing all nonmedical exemptions now could lead to a backlash. A better remedy would be to make waivers more difficult to get. Today, in many jurisdictions, a parent can simply sign a form to opt out.

Instead, parents — two parents, if both are legally responsible for the child — should be required to visit a pediatrician for counseling about the risks of vaccination versus leaving a child unprotected. (Insurance policies and Medicaid should be required to cover the visit.)

Such counseling can be persuasive. About 85 percent of parents who had withheld vaccines changed their mind after group information sessions at the Vaccine Education Center at Children’s Hospital of Philadelphia. States should require a new form and a new counseling session every school year.

Studies have shown that the harder it is to obtain an exemption, the less parents use it. Some are motivated by convenience. Others see the hurdles as a sign of how seriously society regards immunizations.

One way or another, parents who eschew vaccination are going to learn they’ve made a mistake. Smallpox, a great affliction in early America, was almost defeated with a vaccine in the 1800s. When the disease was forgotten and immunization neglected, in the mid-1800s, it again became a mighty killer and had to be fought all over again.

It would be better not to relive that experience with pertussis, measles, mumps, diphtheria, polio or the 11 other communicable diseases that today’s vaccines can prevent.

Editorial by Bloomberg View