The newest whooping cough vaccine is not as effective long-term as the vaccine it replaced, researchers from Kaiser Permanente reported in the current issue of Pediatrics.
Teenagers who had received whole-cell vaccines (DTwP) as children were almost six times less likely to have been diagnosed with pertussis than those who had received acellular vaccines (DTaP), which replaced whole-cell vaccines in the mid-1990s due to safety concerns. Researchers said that the switch could be responsible for the outbreak in whooping cough over the last decade.
“The current vaccine is effective in the short run,” said lead researcher Dr. Nicola Klein, pediatrician and co-director of the Kaiser Permanente Vaccine Study Center in Oakland, Calif. “It just doesn't last as long as we would like.”
A whole-cell vaccine is made from the entire pertussis organism, while acellular vaccines only use specific proteins known to produce immune responses, according to Dr. Tina Tan, pediatrician and vaccination specialist at Northwestern University’s Feinberg School of Medicine. While both effectively combat pertussis, the two types of vaccines generate different antigens--immune response-inducing agents in the body--which may be responsible for the shortened duration of the acellular vaccine's protection, she said.
The U.S. switched to acellular vaccinations due to side effects from the whole-cell vaccine, including fevers and persistent crying.
Pertussis, commonly known as whooping cough, is a respiratory illness characterized by uncontrollable, violent coughing and can be life-threatening for infants. Sixty-five to 70 percent of diagnosed infants under the age of 6 months are hospitalized, Tan said. Ensuring lasting immunization among the adult and adolescent population-- the “vector for transmission to the community”-- can protect infants and other vulnerable persons.
Young children currently receive five doses of the DTaP, which includes immunizations against tetanus and diptheria, before the age of 6 and a booster during adolescence.
However, since the change from DTwP to DTaP, the incidence of whooping cough has been on the rise. In 2012, 41,880 cases were reported, up 52 percent from 2010, in which there were 27,550 cases, according to the Centers for Disease Control and Prevention (CDC). In 2012, Illinois reported 1,859 cases-- the sixth highest in the nation.
“We strongly suspect that the vaccine, in becoming more safe and less reactive for our children, had also given up on some of the long-lasting protection that we would like our kids to have,” said Marcia Levin, vaccine program manager for the Chicago Department of Public Health.
Klein's conclusions are similar.
“A large component of the recent epidemics we've seen-- in California, in Illinois, in New York, Washington and Oregon--do derive in large part from the change to a vaccine that has leaning immunity,” she said.
But don't expect to return to the whole cell vaccine any time soon. The vaccine's side effects, while not life-threatening, are “adverse reactions that people are just not willing to accept in this day and age,” Tan said.
Levin said she predicts that the CDC soon will recommend adolescents and adults receive boosters at five-year intervals to combat the short duration of the current vaccine, although she imagines compliance will be difficult given the infrequency of doctor visits among adults.
Klein said that she is unsure of the efficacy of increasing doses.
“There are a lot of unanswered questions in terms of giving earlier and more frequent boosting, including whether there are more side effects in terms of sore arms or local reactions, whether it's going to prevent more outbreaks, and how well they've been working,” she said.
Instead, she highlighted the need for further research into longer-duration and more effective immunization strategies.
“We really need to move towards building new vaccines,” Klein said.