Whooping cough is making a comeback 40 years after most industrialized countries started vaccinating children, and the culprit seems to be weakening effects of the shot, researchers said on Saturday.

Known also as pertussis, whooping cough can kill infants and can cause a lingering but hard-to-diagnose cough in teens and adults, the experts told an American Society for Microbiology meeting.

They recommend that countries start organized programs to provide booster shots to teens and said doctors need to keep an eye out for the infection when patients show up with coughs.

“Pertussis is a disease that won’t go away,” said Dr. David Hooper, of Massachusetts General Hospital and Harvard Medical School in Boston.

“We have a vaccine for it, but the problem with the vaccine is that immunity wanes after five years. Hospitals and emergency rooms are dealing with outbreaks that continue to occur and are very hard to deal with,” Hooper told a news conference.

Caused by the bacteria Bordetella pertussis, whooping cough is highly infectious. Infected children and adults can give whooping cough to young infants, with fatal results.

13 DIED LAST YEAR

“Young children can die from pertussis, and 13 children died in the United States in 2003,” the U.S. Centers for Disease Control and Prevention says.

“Most deaths occur among unvaccinated children or children too young to be vaccinated.”

Two years ago, 8,296 cases of pertussis were reported in the United States, the CDC said, with incidents steadily increasing since the 1980s. U.S. children get up to five doses of a combined diphtheria, tetanus and pertussis vaccine.

Whooping cough rarely kills an older child or adult, said Dr. Scott Halperin of Dalhousie University in Nova Scotia, Canada. But it can last for weeks.

“Adolescents will have a cough that will last a month to two months,” Halperin told the news conference.

“They will lose sleep. They will miss school. It is a cough most adolescents and adults say they will never forget.”

Nicole Guiso, the chief of the National Center for Infectious Disease at the Institut Pasteur in Paris and colleagues wanted to see if perhaps vaccination had forced the pertussis bacteria to mutate into new forms that could infect vaccinated people.

GERM NOT EVOLVING

They looked at every study that had been done on the bacteria that infected patients and found they were all very similar - suggesting that the bacteria had not evolved.

“It seems that 40 years of vaccination did not change the pathogenicity,” she said.

Dr. Fritz Wirsing von Koenig of the Klinikum Krefeld in Krefeld, Germany said it can be hard to diagnose pertussis in older children and adults.

“When it was a childhood disease, you had these whoops that gave the disease its name,” Von Koenig said. “You really didn’t need a lab (test). Now we are trying to diagnose pertussis in populations which are immune, which have been vaccinated.”

The cough may not have the characteristic intake of breath, he said.

Von Koenig said Germany began vaccinating teens against pertussis in 2000. “This year now we started a program where we vaccinate all young parents and those surrounding ... newborn infants,” he said.

Halperin said teens in Canada get a booster. “So the United States needs to decide what it will be doing about adolescent pertussis and whether immunization should be recommended,” he said.