Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
Relative incidence (with 95% confidence intervals) by duration of the prevaccination risk period. Top series: relative incidence in the 1 to 14 days postvaccination period; Bottom series: relative incidence in the period 1 to days prior to vaccination
