Immunized HCWs can still acquire varicella
But vaccine can prevent severe infections
In implementing varicella immunization programs, infection control professionals are dealing with a critical issue without a clear solution -- health care workers who fail to acquire immunity after vaccination.
Varicella virus vaccine provides 70% to 90% protection against infection and 95% protection against severe disease for seven to 10 years after vaccination, according to the Atlanta-based Centers for Disease Control and Prevention's Advisory Committee on Immunization Practices1. But that leaves 10% to 30% of health care workers who may still be susceptible even after completing the two-dose regimen.
"What you do you do with those people?"says Henrietta Hardnett, RN, nurse epidemiologist at Grady Memorial Hospital in Atlanta. "There's not a whole lot you can do with them because the current tests on the market are not adequate in terms of determining who has developed [immunity]."
According to ACIP, routine testing for varicella immunity after two doses of vaccine is not necessary for the management of vaccinated health care workers who may be exposed to varicella because 99% of persons are seropositive after the second dose. Seroconversion, however, does not always result in full protection against disease, the CDC committee concedes. Still, immunized health care workers who subsequently become infected are less likely to have severe cases of varicella.
"We have already had our first case of an employee who was vaccinated developing chicken pox, but it was a much milder case then he would have had if he had not had the vaccine," Hardnett tells Hospital Infection Control.
Indeed, the worker was febrile for only two days and returned to work on the seventh day after he developed chicken pox. In contrast, prior infections in workers before the availability of the vaccine could result in two weeks of missed work, she adds. Another important factor underscored by the case is that vaccinated workers should be counseled and educated that they still have a risk of developing chicken pox -- though their case will be much less severe. In light of the infection, which developed 14 days after the worker took care of a patient with chicken pox, the hospital is trying to determine whether to attempt restrictions on vaccinated employees -- essentially treating them as nonimmune.
Some hospitals have already made the decision that treating vaccinated health care workers as nonimmune is the best approach, including in some cases barring them from treating patients with known chicken pox. At Santa Clara Valley Medical Center in San Jose, CA, vaccinees are treated as susceptible should they be exposed to chicken pox, says Donna Haiduven, BSN, MSN, CIC, infection control supervisor.
"If you have made a decision to treat a vaccinated person as nonimmune -- as we have -- then you need to be consistent with what you already do with nonimmune employees," she says.
The hospital policy for nonimmune health care workers exposed to varicella -- either at home or through close contact with an infected patient -- allows them to continue working if they monitor their symptoms and wear a surgical mask.2 To allow for the viral incubation period, the mask would be worn at work from day 10 to day 21 after the exposure.
"If they get symptoms they are sent home, so they don't work with chicken pox," she says. "You have a prodromal period where you [symptoms] could be as non-specific as you are getting a cold, having malaise or fatigue."
Use of the strategy prior to the availability of vaccine has involved 49 susceptible employees over an eight-year period. Only four actually developed chicken pox, so the policy saved considerable expense in lost man-hours had the employees simply been furloughed following exposure.
"We potentially saved 540 workdays, but if you are using the approach where you [furlough] people, that would have been 540 days of work lost," Haiduven says.
While immunizing staff can significantly lessen the severity of illness even if "breakthrough" infections occur, the widespread use of the vaccine in the community should eventually decrease the frequency of introductions to health care settings. Thus a vaccine that costs roughly $70 for the two-shot regimen should prove cost-effective over the long run and reduce the incidence of nosocomial outbreaks, the ICPs agree. Still, the issues are somewhat more complicated than originally envisioned when ICPs were hopeful that marketing of the vaccine would eliminate VZV concerns in the hospital.
"It's not as simple as it seemed," Haiduven says. "I remember a year or two ago we kept hearing, 'once the vaccine comes out that will be it.'"
References
1. Centers for Disease Control and Prevention. Prevention of varicella: Recommendations of the Advisory Committee on Immunization Practices. MMWR 1996; 45(No. RR-11):1-36.
2. Haiduven DJ, Hence CP, Stevens DA. Postexposure varicella management of non-immune personnel: An alternative approach. Infect Control Hosp Epidemiol 1994; 15:329-334. *
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