The Effect of Live-Virus Vaccines on Tests for Tuberculosis Infection During the US Immigration Medical Examination: Are Vaccines Causing False-Negative Results?

Background It is not recommended to perform tuberculin skin tests (TSTs) or interferon-γ release assays (IGRAs) in the 4 weeks following live-virus vaccination because these vaccines are thought to increase the risk of false-negative results. Methods We retrospectively analyzed TST and IGRA results for 158 484 US-bound immigrant and refugee children aged 2-14 years who received a required medical examination and live-virus vaccines (measles, mumps, rubella; oral polio; or varicella) overseas during 2014-2022. We created logistic regression models to assess the association between test positivity and vaccination during the critical interval (1-28 days after live-virus vaccination) versus after or before, adjusting for sex, age group, country of examination, and other factors. Results The percentage of positive results and the adjusted odds of a positive IGRA result were higher for children tested during the critical interval (4.6%) than for those tested after (3.5%) (adjusted odds ratio, 1.27 [95% confidence interval, 1.13-1.43) or before (3.3%) (1.26 [1.13-1.41]). The percentage of positive results and the adjusted odds of a positive TST were also higher for children tested during the critical interval (15.7%) than for those tested after (7.2%) (adjusted odds ratio, 2.40 [95% confidence interval, 1.79-3.22]) or before (6.6%) (3.81 [2.80--5.18]). Conclusions The concern that recent administration of live-virus vaccines leads to false-negative TST and IGRA results is not supported by these findings. Instead, we observed a modest increase in positive results among children tested during the critical postvaccination interval, challenging the need for the testing delay.