Measles, Mumps, and Rubella - Centers for Disease Control and ...

14 MMWR May 22, 1998should receive two doses of MMR vaccine. The first dose is administered routinelywhen the child is aged 12–15 months and the second before the child enters school(i.e., at age 4–6 years)(see Routine Vaccination).The clinical diagnosis of rubella is unreliable and should not be considered in assessingimmune status. Because many rash illnesses may mimic rubella infection andmany rubella infections are unrecognized, the only reliable evidence of previous rubellainfection is the presence of serum rubella immunoglobulin G (IgG). Laboratoriesthat regularly perform antibody testing generally provide the most reliable results becausetheir reagents and procedures are more likely to be strictly standardized (seeRubella Case Investigation and Outbreak Control).Postinfection immunity to rubella appears to be long-lasting and is probablylifelong. However, as with other viral diseases, re-exposure to natural rubella occasionallyleads to reinfection without clinical illness or detectable viremia. The risk forCRS among infants born to women reinfected with rubella during pregnancy is minimal(93,94 ). Although data from several studies indicate that levels of vaccineinducedrubella antibodies may decline with time, data from surveillance of rubellaand CRS suggest that waning immunity with increased susceptibility to rubella diseasedoes not occur (28 )(CDC, unpublished data).HI antibody testing was formerly the method most frequently used to screen forrubella antibodies. However, the HI test has been supplanted by other assays of equalor greater sensitivity. EIAs are the most commonly used of these newer commercialassays, but latex agglutination, immunofluorescence assay (IFA), passive hemagglutination,hemolysis-in-gel, and virus neutralization tests are also available.Any antibody level above the standard positive cutoff value of the assay with whichit is measured can be considered evidence of immunity, if the assay is licensed. Whenserum specimens from adults who did not produce antibodies detectable by HI aftervaccination were examined with an equivalently specific but more sensitive test, almostall had detectable antibody (95,96 ). A few children who initially developedantibody detectable by HI apparently “lost” this antibody during follow-up intervals ofup to 16 years (77,97,98 ). However, almost all had antibody detectable by more sensitivetests. In several of these cases, immunity was confirmed by documenting abooster response (i.e., absence of IgM antibody and a rapid rise in IgG antibody) afterrevaccination (62,99 ).Occasionally, persons with documented histories of rubella vaccination have rubellaserum IgG levels that are not clearly positive by ELISA. Such persons can beadministered a dose of MMR vaccine and need not be retested for serologic evidenceof rubella immunity.MumpsPersons generally can be presumed immune to mumps (Table 1) if they have documentationof vaccination with live mumps virus vaccine on or after the first birthday,laboratory evidence of mumps immunity, documentation of physician-diagnosedmumps, or were born before 1957.The demonstration of mumps IgG antibody by any commonly used serologic assayis acceptable evidence of mumps immunity. Persons who have an “equivocal” serologictest result should be considered susceptible to mumps unless they have other