The ACHA (American College Health Association) has the following guidelines regarding varicella:
Two doses of the vaccine for: all college students without other evidence of immunity (e.g., born in the US before 1980, a history of disease, two prior doses of varicella vaccine, or a positive antibody).
And all health sciences students without a history of disease, with one prior dose of vaccine, or with a negative antibody titer should receive a total of two dose of vaccine.
It appears that a titer showing positive antibodies should be sufficient.
The CDC has the following to say (
http://www.cdc.gov/mmwr/preview/mmwrhtml/00042990.htm):
A reliable history of varicella is a valid measure of immunity. Because the rash is distinctive and subclinical cases rarely occur, most parents know if their child has had varicella. A negative history of varicella substantiated by a parent may be more accurate than a self-reported negative history given by an adult. Data from one study indicated that the attack rate following household exposure in parents who reported themselves as being susceptible was 5%; however, among children whose parents reported them as being susceptible, the attack rate was 87%. In children with positive histories, the attack rate was 7% (45).
Serologic tests have been used to assess the accuracy of reported histories of varicella (1,26,42,46,47). In adults, a positive history of varicella is highly predictive of serologic immunity (97%-99% of persons are seropositive); however, the majority of adults who have negative or uncertain histories are also seropositive (71%-93%).
The appropriateness of a laboratory test to detect antibody to VZV depends on the purpose for obtaining the information; tests differ in their ability to detect antibody acquired from natural varicella versus antibody acquired from vaccination -- levels of which are lower than those following natural infection. Likewise, tests that rapidly assess the susceptibility of persons at high risk who are exposed to varicella differ from those used in serologic surveys. Certain tests require equipment or techniques that are not appropriate for general diagnostic laboratories. Thus, the criteria for selection of an antibody-detection assay include test sensitivity and specificity, the length of time required to obtain results, and availability of the assay.
Health-Care Workers *
All susceptible health-care workers should ensure that they are immune to varicella. In health-care institutions, serologic screening of personnel who have a negative or uncertain history of varicella is likely to be cost effective.
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. Testing vaccinees for seropositivity immediately after exposure to VZV is a potentially effective strategy for identifying persons who remain at risk for varicella. Prompt serologic results may be obtained using the LA test. Varicella is unlikely to develop in persons who have detectable antibody; persons who do not have such antibody can be retested in 5-6 days to determine if an anamnestic response is present, in which case development of disease is unlikely. Persons who remain susceptible may be furloughed. Alternatively, persons can be monitored daily to determine clinical status and then furloughed at the onset of manifestations of varicella. Institutional guidelines are needed for the management of exposed vaccinees who do not have detectable antibody and for persons who develop clinical varicella.
More information is needed concerning the risk for transmission of vaccine virus from vaccinees in whom varicella-like rash develops following vaccination. On the basis of available data, the risk appears to be minimal, and the benefits of vaccinating susceptible health-care workers outweigh this potential risk. As a safeguard, institutions may wish to consider precautions for personnel in whom rash develops following vaccination and for other vaccinated personnel who will have contact with susceptible persons at high risk for serious complications.
Vaccination should be considered for unvaccinated health-care workers who are exposed to varicella and whose immunity is not documented. However, because the protective effects of postexposure vaccination are unknown, persons vaccinated after an exposure should be managed in the manner recommended for unvaccinated persons.
Both healthy and immunocompromised children and adults who have positive histories of varicella (except for bone-marrow transplant recipients) can be considered immune (see Recommendations for the Use of Varicella Virus Vaccine). However, varicella may develop in some infants after exposure despite the presence of detectable antibody, although in most circumstances such illness is less severe than the illness occurring in infants who do not have detectable antibody. Therefore, sensitive assays may not be useful in assessing whether clinical disease will develop in neonates or young infants exposed to varicella.
Revised criteria for evidence of immunuty to varicella includes
any of the following:
1. Documentation of age-appropriate vaccination:
a. Preschool-aged chilren greater than 12 months of age: one dose...etc.
2.
Laboratory evidence of immunity or laboratory confirmation of disease
I have been unable to find anything suggesting health care workers should receive vaccinations despite proof of immunity. I'm baffled.
