Gardasil plus flu vaccine, false positive HIV?(INFLUENZA VACCINATION AND INDETERMINATE WESTERN BLOT TESTS) (FLU SHOT AND FALSE POSITIVE HIV TESTS)

Question

A week ago my 17-year-old daughter received a letter from Red Cross indicating she screened HIV positive after donating at a recent blood drive. Results were HIV-1/HIV-2 Positive, Confirmatory Indeterminate, NAT Negative. Retesting was done at a hospital lab. Results are HIV (weak) negative and we await Confirmatory results. My daughter appears to have no risk factors. She is a virgin, has no history of sexual activity whatsoever, no tattoos, no IV drug use. Ten days before the blood donation she received (her first ever) flu vaccine and also the second of three Gardasil shots. She was also prescribed Provera a month earlier. After reading previous posts I believe you draw no correlation between vaccines and false positive HIV tests, however there does seem to be recent information to the contrary. Information published in March 2006 in the New England Journal of Medicine asserts recent inoculation with any brand of influenza vaccine was significantly associated with a false positive screening assay for HIV antibodies. Guidelines of both Johns Hopkins and the New York State Department of Health list influenza vaccination as a known cause of indeterminate results on Western blotting for HIV antibodies. Given the escalating international awareness of various influenza strains, it is very important to remind patients and clinicians that influenza vaccination may cause cross-reactivity with HIV antibody assays. I'm not qualified to debate the validity of this information, but it is somewhat comforting for a family in a situation like ours to think that a vaccine might be the issue. My question: What is your opinion of the likelihood of an HIV positive confirmation considering my daughters history? Thank you.

Answer

Hello,

Thanks for your post. Yes, we are trying to get this more recent information out to a wider audience. The influenza vaccine changes from year to year to cover the most likely flu strain candidates for the coming flu season. We do have recent information that flu vaccination can cause some degree of nonspecific cross-reacting antibodies, which can confound HIV-antibody tests. Generally speaking, these cross-reacting antibodies cause "indeterminate" rather than "false positive" HIV tests. Please note a reactive ELISA with subsequent indeterminate Western Blot is considered to be an "indeterminate" HIV test result, not a positive test! HIV testing center and certainly HIV specialists are well aware of these potential complicating factors and we have methods for sorting out serological results that are either in dispute or indeterminate.

In your daughter's case of essentially no potential HIV exposure and a recent flu vaccine, you can rest assured her indeterminate Western Blot is not related to HIV seroconversion, but rather to the detection of cross-reacting antibodies. That her NAT was negative confirms this fact, because NAT testing does not rely on antibody detection.

Happiest Holidays to you and your entire family.

Dr. Bob