Whooping Cough Risks Among Kids Increase

Pertussis vaccine effectiveness appears to wear off as rates increased over time

(RxWiki News) Vaccines save lives by preventing a person from getting a disease or dramatically lowering their risks for the disease. But vaccines are not perfect. Their protection can wear off.

A recent study found more evidence that the vaccine for whooping cough is wearing off sooner than researchers expected.

Whooping cough is the common name for pertussis. It is a respiratory disease caused by a bacteria that can lead to months of intense coughing.

The researchers in this study found that the risk of catching pertussis among fully vaccinated children in two states increased considerably over a six year period.

"Follow the CDC vaccination schedule."

The study, led by Sara Y. Tartof, PhD, MPH, of the Centers for Disease Control and Prevention, aimed to understand how the risk of catching pertussis changed as time passed after children were vaccinated against it.

The disease can be fatal to babies, especially those under 2 months old who have not received their first vaccine for it.

The researchers tracked children in Minnesota and Oregon who were born between 1998 and 2003 and had received all five shots for the DTaP. These shots start with an initial one at 2 months old, with four booster shots following throughout early childhood.

DTaP stands for "diphtheria, tetanus and acellular pertussis." It is the only vaccine given in the US to protect against pertussis, and it also includes the vaccines for the diseases tetanus and diphtheria.

The study included 224,378 children from Minnesota and 179,011 children from Oregon. Both Minnesota and Oregon had very high numbers of pertussis cases in 2010 and 2012.

The researchers reviewed 458 of the children in the Minnesota group and 89 of the children in the Oregon group for the full time period studied. Over that time, the number of pertussis cases that occurred rose each year.

During the first year of follow-up of the study, a rate of 15.6 out of 100,000 children contracted pertussis in Minnesota. By the sixth year of the study, that rate had risen to 138.4 out of 100,000 children.

In Oregon, the rate of pertussis in the first year was 6.2 out of 100,000 children, which rose to 24.4 out of 100,000 children by the sixth year of the study.

In Minnesota, a child was twice as likely in the second year of the study as in the first year to contract pertussis. By the sixth year, a child was nine times more likely to catch whooping cough than they were in the first year of the study.

In Oregon, a child was 30 percent more likely to catch pertussis in the second year of the study than in the first year. By the sixth year, children were four times more likely to catch pertussis than they were in the first year.

"This rise is likely attributable in part to waning immunity from DTaP vaccines," the researchers wrote. Past studies in the last year have shown that the vaccine's effectiveness decreases over time more quickly than was expected.

This discovery of the decreasing effectiveness of the vaccine over time led the CDC's immunization policy group to recommend that pregnant women be vaccinated with the TDaP (the adult version of the DTaP) each time they are pregnant, even if they had the shot within the past five years.

The CDC group, called the Advisory Committee for Immunization Practices, hopes the extra shot during pregnancy will offer a bit of extra protection to the baby during its first two months of life.

The vaccine is still effective in the couple of years after it is given, and babies who receive the vaccine on time will be protected by it from whooping cough. Babies are at the highest risk from dying from the disease.

It is older schoolchildren and teenagers who are losing immunity from the vaccine as they grow older. So far, the CDC committee has not made recommendations for extra boosters of the vaccine.

Thomas Seman, MD, a pediatrician at North Shore Pediatrics in Danvers, Mass. and a dailyRx expert, said researchers have known for a while that the DTaP vaccine offers shorter-lasting protection than the old one even while it has fewer side effects. Yet this fact means it's all the more important to vaccinate against the disease.

"As the study points out, the preteens and the teens are at the highest risk of a waning immunity to pertussis," Dr. Seman said. "These ages also coincide with children being the most active and in teens starting babysitting, working and volunteering. All of these activities increase the exposure of the disease to others who may have a compromised immune system due to age or illness."

He said this illness can be particularly dangerous for younger children and babies, as well as those with other respiratory conditions.

"Infants and young children who contract pertussis not only have a hard time breathing, but in the very young, the infection causes the brain to stop telling the lungs to breathe, further placing the child at risk," Dr. Seman said. "Those with asthma who contract the disease have a very difficult time with breathing and have a much slower recovery, oftentimes needing hospitalization and, on occasion, even intubation to help them with their recovery."

Dr. Seman added that those with weakened immune systems or taking immunosuppressants for a condition are also particularly at risk for catching the disease.

"Therefore, for all of those we can vaccinate, even knowing that over time their immunity wanes, we can still protect our children, sick and elderly from this devastating disease," he said.

Meanwhile, various research teams throughout the world are working on a more effective vaccine.

The study was published March 11 in the journal Pediatrics. The research did not receive external funding. The authors declared no conflicts of interest.

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Review Date: 
March 9, 2013