We have had three employees who have tested positive for influenza by nasal swab within 2 weeks of receiving an inactivated influenza vaccine (IIV4). Is there a time period after receiving IIV4 that a nasal swab can give a false positive result?

Inactivated influenza vaccines are not known to cause false positive nasal swab tests. The results may indicate real infections; however, false positive test results are possible with rapid tests, and these are more likely to occur if the tests are done 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.