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Immunizations, Viruses, & Inconclusive Test Results

Dec 11, 1996

I just went to get an HIV test and during the pretest counseling I was asked if I'd recently had any immunizations or viral infections. I did get a bad cold or the flu about 1 wk ago, and about 1 month ago had the second shot for Hepatitis B immunization (I got the first shot about two months ago). The counselor that I saw told me that these immunization shots and the flu might cause test results to be inconclusive. Does this often happen? What action do you recommend I take if the results are inconclusive? It may help to know that my last risky activity occurred 6 months ago -- is it safe to assume that if I was infected the test would otherwise be positive by now? Thank you for all of your help. Your answers and all the hard work you do is certainly much appreciated.s

Response from Mr. Sowadsky

Hi. Thank you for your question.

Several years ago, it was found that the flu shots were causing false positive ELISA tests, but negative Confirmatory tests like the Western Blot and the IFA. If an ELISA test is positive, but the confirmatory tests are negative, this is a negative result overall, not an indeterminate test. Therefore, even people who got these vaccinations were given a negative test result overall. The problems with flu shots causing false positives on ELISA tests, have now apparently been resolved, so this should not pose a problem anymore.

An inconclusive test is one where the Confirmatory test (like the Western Blot) cannot determine whether a person is infected or not. This is usually due to something cross reacting with the test, or a person who has just recently been infected with HIV, and are just starting to produce antibodies. In this case, a person would usually be asked to re-take the HIV test several weeks later (usually 4-6 weeks), to see whether they are infected or not. I am not aware of vaccinations causing indeterminate Confirmatory tests.

Other vaccinations (including Hepatitis B), have not reacted with the HIV tests, so this is not a problem. By the way, Hepatitis B vaccinations are usually done at day one, the second shot 1 month after the first (not 2 months), and the third and final shot 6 months after the first.

Also cold and flu viruses should not affect the HIV antibody tests.

Since it has now been 6 months since your possible exposure, your test results should now be more than 99% accurate, as good as any test in medicine could be. So if your tests are negative, there would be no need for retesting.

If you have any further questions please e-mail me at "" or call me at 1-800-842-AIDS.

When to re-test when negative twice
How quickly can HIV antigens be detected after infection

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