Q: We have had three employees who have tested positive for influenza by nasal swab within two weeks of receiving Fluarix Quadrivalent (GlaxoSmithKline) vaccine. Is there a time period after receiving influenza vaccine that a nasal swab can give a false positive result?
A: Inactivated influenza vaccines, including Fluarix, are not known to cause false positive nasal swab tests. However, false positive test results are possible with rapid tests, and these are more likely to occur when influenza prevalence in the area is low. For more information regarding interpretation of rapid influenza tests, see www.cdc.gov/flu/professionals/diagnosis/rapidlab.htm.
A: The only way to determine whether the rash is caused by wild-type varicella or vaccine virus is to try to isolate virus from the rash and send it to a laboratory that is capable of differentiating wild and vaccine-type virus. This is generally not practical. Given the history, the conservative approach is to assume she has an active case of chickenpox and act according to your infection control guidelines.
A: The Advisory Committee on Immunization Practices (ACIP) does not recommend more than one dose of influenza vaccine per season, except for certain children being vaccinated for the first time. The 2017–18 influenza vaccine may be available near the end of her pregnancy, so she can be given a dose of next year’s formulation at that time.
A: Recent Tdap vaccination does not affect PCR testing. PCR tests are used to detect DNA sequences of the Bordetella pertussis bacterium. PCR tests are very sensitive and could give a false positive result for other reasons. For more information on the interpretation of pertussis diagnostic tests, see
www.cdc.gov/pertussis/clinical/diagnostic-testing/diagnosis-confirmation.html.
A: Neither the ACIP nor the manufacturers address the timing of vaccination and dialysis. Persons with end-stage renal disease including predialysis, hemodialysis, peritoneal dialysis and home dialysis should be tested for hepatitis B surface antibody (anti-HBs) one to two months after vaccination, and annually. If the anti-HBs level is below 10mIU/mL, they should be revaccinated. See www.cdc.gov/mmwr/PDF/rr/rr5516.pdf, page 27, for more information.