On March 22, 2002, Internet-based reports (IBRs) were added to the Vaccine Adverse Event Reporting System (VAERS) to allow rapid, expedited reporting of adverse events (AEs) in anticipation of wider use of counter-bioterrorism vaccines such as those against smallpox and anthrax.


To evaluate the impact of IBRs on the timeliness and completeness of vaccine AE reporting.


To evaluate timeliness and completeness, we compared the proportions of IBRs with non–Internet-based reports (NIBRs). Report interval was analyzed for timeliness and age at vaccination, birth date, and onset date for report completeness. To evaluate the impact of the smallpox vaccination program, we compared smallpox vaccine reports separately. Because influenza vaccine is the most widely used vaccine in adults each year, we compared influenza vaccine reports separately.


During the study period, VAERS received 54 364 NIBRs (85.8%) and 9008 IBRs (14.2%). Sixteen percent (1455) of IBRs followed smallpox vaccination. Overall, for all vaccines and for smallpox vaccine alone, IBRs had a greater proportion of completeness and a shorter report interval. The proportion of most frequently reported AEs did not differ between IBRs and NIBRs. A higher proportion of adults (18–64 years old) who received influenza vaccine chose to complete an IBR (62% vs 48%).


The improved timeliness and completeness of IBRs allow VAERS to more rapidly detect new or rare vaccine AEs. This important advantage is critical in times of increased public concern about vaccine safety. Clinical vaccine providers should be aware of VAERS and use IBRs whenever feasible to report vaccine AEs.

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