Is Prior Smallpox Vaccination Effective Against Mpox?

Between 2002 and 2017, 2.6 million U.S. military personnel received either a live replicating (Dryvax or ACAM2000) or live nonreplicating (JYNNEOS) smallpox vaccine. To assess the effectiveness of smallpox vaccination against mpox during the recent outbreak, investigators queried Veterans Affairs (VA) and Department of Defense data in a retrospective, test-negative, case–control study with logistic regression to determine factors (including vaccination) associated with a positive orthopox PCR test result.

From July through October 2022, a total of 1014 military personnel had symptoms compatible with mpox and underwent orthopox testing. Median time since smallpox vaccination was 13 years. Of the 293 participants with a positive PCR test, 3% h…