Rapid immune responses may make booster vaccine useful during pertussis outbreaks

About half of health care personnel who participated in a tetanus toxoids, reduced diphtheria toxoids and acellular pertussis vaccine, adsorbed vaccination campaign following an outbreak of pertussis-like illness achieved a protective immune response one week following vaccination, suggesting that a booster dose may help reduce the duration and cost of hospital outbreaks.

Health care workers are a particularly important target population for outbreak-control efforts because they can spread illness to vulnerable patients including infants and the elderly.

Researchers from the Dartmouth Hitchock Medical Center in Lebanon, New Hampshire and the Vanderbilt University School of Medicine in Nashville, enrolled 115 health care workers aged 19 to 79 years (median age 45) to participate in a vaccination campaign in May of 2006 and followed participants for four weeks following vaccination. Serum samples were collected each week to measure antibody to pertussis toxoids, filamentous hemagglutinin, pertactin and fimbriae types 2 and 3.

About 88% to 94% of participants achieved a booster response two weeks following vaccination and this increased to 92% at four weeks. None of the patients reported respiratory illness during the study period, according to the researchers.

Although the dates for prior whole-cell pertussis vaccination were not documented in this study, 91 participants reported having received the vaccine, three denied previous vaccination and 21 were unsure of their vaccination status.

Nils H. Birkebaek, MD, of the department of pediatrics at Aarhus University Hospital in Aarhus, Denmark, suggested that pinpointing when prior vaccination took place, a comparison with a non-vaccinated control group and a longer follow-up period would provide a more accurate estimate of the booster dose’s efficacy.

He also pointed out that vaccine immunogenicity in people aged older than 64 remains unknown and the vaccine has yet to be approved for use in this population.

Currently, Tdap is licensed for single dose administration; however, multiple booster doses may be necessary among health care workers as the duration of protection is estimated to be about six years, according to Birkebaek.

“The next step is to investigate whether a Tdap booster vaccination for health care personnel with waning pertussis immunity at the time of a pertussis outbreak, can reduce the need for antimicrobial prophylaxis among health care personnel who are exposed to pertussis-infected patients, and whether a booster vaccination can reduce the duration and cost of pertussis outbreaks in hospitals,” he wrote. – by Nicole Blazek

Kirkland KB et al. Clin Infect Dis. 2009;48:584-7.

Pertussis exposures remain a difficult problem for hospital infection control programs, especially in children’s hospitals. Although diagnosis has improved and become faster with the widespread use of PCR, investigations of possible or confirmed cases of pertussis are difficult, time consuming and expensive. In one calendar year, Texas Children’s Hospital spent more than $20,000 on antibiotics for possibly-exposed hospital employees. This study supports the concept that the use of Tdap can be added to the arsenal of infection control to prevent transmission from health care workers after an exposure has occurred.

A related issue is the 2006 ACIP recommendation that all health care personnel receive a Tdap booster. Although published data are scant, it appears that individual providers and many health care institutions have been slow to endorse and support universal vaccination of health care personnel with Tdap. Why is this? Why do we have a difficult time getting health care personnel influenza vaccination rates above 65%? Why don’t all heath care institutions mandate these vaccinations?

If Tdap vaccination were universal and the studies were performed to demonstrate the contribution of this vaccination to preventing pertussis transmission, we might not have to worry about pertussis outbreak control anymore.

– Jeffrey R. Starke, MD

Infectious Diseases in Children Editorial Board