Immunosuppressive treatments reduce long-term immunity to smallpox among patients with breast cancer.

Background: Mass vaccination is the principal preventive measure against a smallpox outbreak after an act of bioterrorism. Vaccination of subjects who received immunosuppressive therapies is problematic because of smallpox vaccine reactogenicity. Moreover, long-term immunity to vaccinia might be affected.

Objective: The objective of the study was to examine the effect of cytotoxic chemotherapy on long-term immunity to vaccinia.

Methods: In a case-control study, 67 patients with breast cancer who received cytotoxic chemotherapy and who were disease free for at least 1 year were matched with healthy controls according to age, sex, and the number of smallpox vaccinations received. Markers of immunity to smallpox were examined. Forty-one patients with breast cancer who did not receive chemotherapy were used to assess the affect of cancer and radiotherapy on immunity to smallpox.

Results: Patients with breast cancer who received chemotherapy had lower levels of vaccinia total immunoglobulin G and immunoglobulin G1 (expressed as enzyme-linked immunosorbent assay units per milliliter), neutralizing antibodies, vaccinia:memory B cell ratio (expressed as a percentage), and interferon-gamma level (expressed as picograms per milliliter), compared with healthy control individuals.

Conclusions: Immunity to smallpox is reduced after receipt of chemotherapy for breast cancer. This finding should be considered when planning smallpox vaccination campaigns. The effect of immunosuppressive treatments on persistence of immunity should be tested with respect to additional vaccines or natural infections.