Does an IgM (Immunoglobulin M) titer for chickenpox show if a patient has gotten the varicella vaccine or does it require an IgG (Immunoglobulin G) titer?

Varicella Immunity Testing: IgG vs IgM for Vaccine Status Determination

IgG testing is required to determine if a patient has received the varicella vaccine, as IgM is only useful for detecting recent infection but not for confirming vaccine-induced immunity. 1

Understanding Antibody Response to Varicella Vaccination

The immune response to varicella vaccination differs from natural infection in several important ways:

• IgG antibodies develop after vaccination and persist long-term, serving as the primary marker of immunity 2
• IgM antibodies appear transiently during acute infection but are not reliable indicators of vaccination status 2
• Antibody response timeline: After vaccination, IgG antibodies to phase II antigen typically develop within 7-15 days, with approximately 76-90% of children developing protective antibody levels after a single dose 2

Testing Considerations for Vaccine-Induced Immunity

Preferred Testing Method

• IgG testing is the standard method for determining immunity status after vaccination 1
• Commercial enzyme immunoassay (EIA) tests for IgG are widely available and preferred for screening purposes 1

Testing Limitations

• Standard commercial assays may sometimes fail to detect vaccine-induced immunity despite actual protection 1, 3
• This occurs because commercial tests were originally designed to detect the higher antibody levels from natural infection rather than the lower levels induced by vaccination 3
• After vaccination, approximately 25-34% of vaccinated individuals may test negative for VZV IgG despite being protected 3, 4

Special Considerations

False Negatives in Vaccinated Individuals

• Some vaccinated individuals develop adequate cell-mediated immunity despite having low or undetectable antibody levels 3
• In these cases, more sensitive assays like fluorescent antibody to membrane antigen (FAMA) or latex agglutination may detect antibodies that standard ELISA tests miss 3

When to Consider Additional Testing

• For healthcare workers or immunocompromised patients with negative standard IgG results despite documented vaccination, more sensitive testing methods may be warranted 1, 3
• In cases of persistent seronegativity after vaccination, cell-mediated immunity testing may provide additional information about protection status 3

Response to Revaccination

• Studies show that individuals with negative IgG status after two doses of vaccine can achieve positive IgG status after a third dose 4, 5
• After revaccination, seroconversion rates approach 100% in previously seronegative individuals 4

Clinical Algorithm for Determining Varicella Immunity

1. First step: Test for VZV IgG (not IgM) to determine immunity status
2. If IgG positive: Consider the patient immune to varicella
3. If IgG negative with documented vaccination history:
   • Consider more sensitive testing methods (FAMA or latex agglutination) if available
   • Consider administering an additional vaccine dose followed by repeat IgG testing
4. If IgG negative without vaccination history: Recommend complete vaccination series

Remember that the CDC does not recommend post-vaccination serologic testing due to the limitations of commercial assays in detecting vaccine-induced immunity 1.