Health officials are searching for the causes of an outbreak of pertussis across the country, including a surge of reported cases in Massachusetts. In this week’s New England Journal of Medicine, California pediatrician Dr. James D. Cherry offers some ideas.

Pertussis, also known as whooping cough, is a bacterial infection characterized by a severe, long-lasting cough that can be especially dangerous for infants. Dr. Larry Madoff of the Massachusetts Department of Public Health said Wednesday that the number of reported cases so far this year is more than three times higher than the number reported during the same period in 2011.

People are more aware of the disease and physicians now have improved ways of testing for it, so diagnosis and reporting may be up, Cherry said in a perspective piece in the journal.

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Especially concerning, he said, is that today’s DTaP shots, which also vaccinate for tetanus and diphtheria, are less effective than those used in the past. The vaccine was introduced in the mid-’90s because of safety concerns about the previous formula.

Epidemics of the disease in 2005, 2010, and this year “suggest that failure of the DTaP vaccine is a matter of serious concern,” said Cherry, a professor at the David Geffen School of Medicine at the University of California, Los Angeles who specializes in infectious diseases at Mattel Children’s Hospital.

Before the use of pertussis vaccines in the United States, he said, the average incidence was 157 cases per 100,000 people in the early 1960s. By 1973, that was cut to 1 case per 100,000 people. Some states this year have seen a return to the incidence rate of old. But nationally, Cherry notes, the incidence is still a small fraction—about one twenty-third—of what was seen during an epidemic year in the 1930s.

“Nevertheless, I believe that better vaccines are something that industry, the Center for Biologics Evaluation and Research of the Food and Drug Administration, and pertussis experts should begin working on immediately,” he writes.

In the meantime, families should use the “cocooning” strategy of vaccinating adults who are in frequent contact with infants. Schoolchildren in Massachusetts are required to be vaccinated for pertussis. Adults can receive a booster shot.