(Reuters Health) - Even though vaccinations don’t always prevent whooping cough, people have milder symptoms of the respiratory illness and lower odds of serious complications with the vaccine than without it, a U.S. study suggests.

FILE PHOTO: A nurse displays a tetanus, diphtheria and pertussis whooping cough vaccine at a free medical and dental health clinic in Los Angeles, California, U.S., April 27, 2016. REUTERS/Lucy Nicholson

More than three in four cases of whooping cough, or pertussis, occurred in people who were up to date on their vaccinations, the analysis of multistate disease surveillance data found.

Babies and young children had 60 percent lower odds of severe infections, however, when they had received all recommended childhood pertussis vaccinations. And, with up-to-date vaccinations, most infected children and adults had 30 percent lower odds of severe vomiting, a hallmark of more serious infections.

“These findings are very important because they show that even though pertussis vaccines do not prevent all cases of pertussis, breakthrough cases that occur in vaccinated people are less likely to be severe,” said lead study author Lucy McNamara, of the National Center for Immunization and Respiratory Diseases at the U.S. Centers for Disease Control and Prevention (CDC) in Atlanta.

“That means fewer hospitalizations and serious complications for patients,” McNamara said by email.

The bacterium Bordetella pertussis causes whooping cough, which gets its nickname from the sounds patients make as they gasp for air during intense coughing fits. Pertussis is highly contagious and easily spread when an infected individual coughs or sneezes. Many babies less than 1 year old who catch pertussis require hospitalization for serious complications like pneumonia or brain disorders.

The CDC recommends that children get five doses of the DTaP vaccine for tetnanus, diphtheria and acellular pertussis at ages 2, 4 and 6 months, between ages 15 and 18 months, and between ages 4 and 6 years.

A single dose of a different version of the vaccine, called Tdap, is recommended for people 11 through 64 years old.

For the current study, researchers examined data on 9,801 pertussis cases from 2010 to 2012 in U.S. patients at least 3 months old. Cases came from statewide infection registries in Connecticut, Minnesota and New Mexico as well as from select counties in Colorado, New York and Oregon.

Almost four in five cases occurred in patients under 20 years old, and more than half of infections happened in children 12 or younger.

The study wasn’t a controlled experiment designed to prove that vaccination reduces the severity of the infections that shots don’t prevent.

One limitation of the study is that it’s possible people who get all recommended vaccinations on time also have other healthy behaviors that make them less likely to catch pertussis or to suffer from severe symptoms, the authors note.

Even so, the findings offer fresh evidence that the current version of the vaccine is working, said Dr. Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine in Houston.

The CDC changed the vaccine in the 1990s from a version using whole cells known as DTP to the current version, known as DTap, which has fewer side effects such as fevers, Hotez, said by email.

Even though the total number of pertussis cases has crept up a little bit with DTaP, the findings suggest it’s doing a good job at protecting infants against severe cases, added Hotez, who wasn’t involved in the study.

“This is good news since it provides further evidence that the U.S. pertussis vaccine program can continue to work with DTaP,” Hotez said.

While much of the previous research has focused on childhood vaccination, the current study shows that adults, too, can benefit from the pertussis vaccine even if they still get whooping cough, said Dr. Kevin Schwartz, a public health researcher at the University of Toronto who wasn’t involved in the study

“The biggest danger of adults getting pertussis is they can spread the infection to those who are at the highest risk of pertussis-related complications and death, including young children who haven’t received any or all of their vaccinations yet,” Schwartz said by email.

“Even though vaccine protection decreases over time, the best way to protect babies from severe pertussis is to make sure everyone is up-to-date with their recommended pertussis vaccines,” Schwartz added.

SOURCE: bit.ly/2v3nHyO Clinical Infectious Diseases, online July 8, 2017.