Pertussis immunity wanes over time

Tdap booster important for HCWs

Health care workers who received the acellular pertussis vaccine as children may have little immunity as adults, a new study suggests.

An analysis of about 10,000 vaccinated children in northern California found that in the five years after the fifth dose of DTap, the risk of acquiring pertussis rose by 42% a year as immunity waned.1

The study did not address the immunity of adults, but the findings raise concerns about young health care workers who were immunized as children with the acellular vaccine, says William Schaffner, MD, chair of the Department of Preventive Medicine at Vanderbilt University in Nashville, TN, and past president of the National Foundation for Infectious Diseases.

DTaP (diphtheria, tetanus and acellular pertussis) came into use in the 1990s as health providers sought to avoid the adverse effects of the whole cell vaccine, including fever, pain at the injection site, and in rare cases, seizures and high fevers.

"[The study] quantifies the speed with which the immunity wanes," says Schaffner." That has surprised many people, myself included. The fall-off in immunity of 42% per year. I had no idea it was that fast."

The study analyzed vaccination history and pertussis PCR results from January 2006 to June 2011 for children who were between the ages of 4 and 12. Some 277 of them were pertussis PCR positive, 3,318 were PCR negative, and 6,086 were matched controls from the general population of Kaiser Permanente Northern California.

Children aged 8 to 11 years had the highest incidence of pertussis, which also pointed to the waning immunity after five doses. The pertussis cases were mild or moderate, and none required hospitalization or led to death, the authors said.

Few HCWs receive Tdap

What do these findings mean for health care workers? They underscore the importance of booster vaccination of health care workers with Tdap, says Schaffner. Surveys show that only about 20% of health care workers have received the Tdap vaccine.

"We need to implement vigorously and comprehensively the current regulations," he says.

Pertussis has become a growing concern as outbreaks ripple across the nation. As of September 20, the Centers for Disease Control and Prevention reported 29,000 cases and 14-pertussis-related deaths. In 48 states, pertussis activity was higher this year than in 2011. For example, in Washington state, 4,115 cases were reported as of September 15 — almost 10 times as many as in the same period in 2011.

Amid the concerns about waning immunity, the Advisory Committee on Immunization Practices, an expert panel that reports to the CDC, is expected to consider changes in recommendations. "There's a question about whether more frequent boosters may be necessary," Schaffner says.

If public health authorities determine there needs to be a new booster that provides acellular pertussis only (without diphtheria and tetanus), then the vaccine manufacturers would need to seek FDA approval, he says. Vaccine makers also might seek to make a more effective vaccine.

Older workers who received the whole cell vaccine as children may have more lasting immunity. But they still need the one-time Tdap booster, says Schaffner.

"Older health care workers are more likely to be protected, but we cannot be certain about that," he says. "Everyone in the population should be vaccinated."

Reference

1. Klein NP, Bartlett J, Rowhani-Rahbar A, et al. Waning protection after fifth dose of acellular pertussis vaccine in children. N Engl J Med 2012;367:1012-1019.