Pertussis Protection Declined Faster Without Booster Dose

Whooping cough vaccine has early effectiveness but starts to fade later

(RxWiki News) The vaccine that prevents whooping cough fades earlier than expected in older children, based on recent research. But what about for babies and toddlers?

A recent study found that the vaccine was very effective early in children's lives, but it did start to wane when children were 2 and 3 years old.

Whooping cough, officially known as pertussis, is one of the diseases the DTaP shot is supposed to protect against. The other two diseases this vaccine protects against are tetanus and diphtheria.

The findings of this study revealed the importance of getting babies the DTaP as soon as possible and possibly getting a booster shot as toddlers.

"Discuss the CDC recommended immunization schedule with your doctor."

This study, led by Helen E. Quinn, PhD, of the Australian National Centre for Immunisation Research and Surveillance of Vaccine Preventable Diseases, looked at the effectiveness of the DTaP vaccine for children up to age 3.

Past research has shown that the vaccine's effectiveness wanes after children receive their fifth dose at age 6.

The researchers in this study wanted to better understand the vaccine's effectiveness through the first three doses, given when children are between 2 months and 4 years old.

These researchers identified 4,584 Australian children, aged 2 months to nearly 4 years old, who had pertussis at some point between January 2005 and December 2009 and whose immunization history was available.

For each child with pertussis, the researchers matched 20 children without pertussis who had been born the day before or after the one with pertussis and lived in the same geographical region.

With these two groups, the researchers compared the number of doses of the DTaP the children had received.

An analysis of the results revealed that the vaccine's effectiveness in preventing hospitalization for pertussis increased from 55 percent with one dose before 4 months old to 83 percent for the second dose, received before 6 months of age.

In other words, children who had received their second dose of DTaP were two thirds more likely to avoid catching pertussis that required hospitalization.

Meanwhile, the effectiveness of receiving the third dose of DTaP in preventing all reported pertussis was 83.5 percent for children between 6 and 11 months old. However, by the time children were between 2 and 3 years old, the effectiveness of three doses of DTaP had dropped to 71 percent for preventing pertussis.

By the time the children were between 3 and 4 years old, the effectiveness of the vaccine in preventing pertussis had dropped to 59 percent.

"DTaP provided good protection against pertussis in the first year of life from the first dose," the researchers concluded.

"Without a booster dose, the effectiveness of three doses waned more rapidly from 2 to 4 years of age than previously documented for children older than 6 years of age who had received 5 doses," they wrote.

These researchers said their findings provide support for giving babies the first dose of DTaP as soon as possible, currently approved by regulatory agencies at 6 weeks old.

They also recommend a booster dose for 2-year-olds, especially if their mothers had received a Tdap booster during the third trimester of pregnancy, as currently recommended.

According to Thomas Seman, MD, a pediatrician at North Shore Pediatrics in Danvers, Mass., the current CDC recommendations call for three doses of DTaP by 6 months and a fourth dose between 18 and 24 months, followed by a booster at 4 to 5 years old.

"This schedule should help counteract the effects of the waning immunity that was seen in this study," he said.

"We have known for some time that the acellular pertussis vaccine that we now use is slightly less effective than the whole cell vaccine, but it has a much better safety profile," Dr. Seman said.

"If everyone on the age group gets vaccinated, then there is herd immunity; should there be a child whose immunity wanes faster, he/ she will still be protected by those whose immunities are stable and will not get the disease when exposed," he said.

This study was published February 10 in the journal Pediatrics. The research was commissioned by the Australian Commonwealth Department of Health and Ageing with funding from the National Centre for Immunisation Research and Surveillance of Vaccine Preventable Diseases.

One author worked on a study that used vaccines provided by GlaxoSmithKline, and another worked on a rotavirus study funded partly by GSK Australia. No other conflicts of interest were reported.

Review Date: 
February 10, 2014