Deaths and Encephalitis-Linked Symptoms Reported to VAERS Following Administration of Hepatitis B Vaccines to Infants in the United States from 1990–2025

Background/Objectives: Hepatitis B vaccines (HBVs) have been recommended since 1991 for all U.S. infants starting at birth. Several studies have examined associated reports to the U.S. Vaccine Adverse Events Reporting System (VAERS) and found no unexpected safety signals, but no study has systematically quantified and characterized the reports. Methods: A range of outcomes reported to VAERS between 1990 and 2025 was assessed, stratifying by HBV type, age, sex, and vaccine dose. The outcomes included death, SIDS, seizures, developmental delay, encephalitis; and four symptom groups that may reflect potential signs of encephalitis (crying, fever, sleepiness, and gastrointestinal disorders). Results: 1,793 deaths have been reported to VAERS since 1990 following administration of HBVs. Of these, 1493 were for infants aged 0-12 months, of whom 64% were in the 2-3 month age group and 60% were male. Most death reports occurred in infants receiving HBV co-administered with other vaccines or in combination shots like Comvax and Pediarix. The rate of SIDS was nearly twice as high in males compared to females in the 2-3 month age group. Other adverse events were reported at more similar rates for males and females, but all outcomes in infants occurred most frequently at age 2-3 months. Conclusions: Male infants aged 2-3 months who receive multiple vaccines at once appear more vulnerable to adverse events than other groups. Since the extent of underreporting to VAERS is not well known, characterizing the patterns in the existing reports is more informative than judging whether they are cause for concern.