The incidence of hepatitis A (HepA) declined in the U.S. following the introduction of hepatitis A vaccines, but a recent upswing in widespread outbreaks has public health officials concerned.

A recent study in Public Health Reports describes HepA epidemiology in the U.S., identifying susceptible populations over time. The emphasis is on the critical need for improved HepA vaccination coverage, especially among adults at increased risk for HepA.

CDC researchers calculated the HepA incidence rates for sociodemographic characteristics and percentages for risk factors and clinical outcomes for HepA cases reported to the National Notifiable Diseases Surveillance System from 1990 to 2020. Using data from the National Health and Nutrition Examination Survey, the study team created nationally representative estimates and 95% CIs of HepA seroprevalence from 1976 to March 2020 and self-reported HepA vaccination coverage from 1999 to March 2020 for the noninstitutionalized civilian U.S. population.

The results indicated that overall, the rate per 100,000 population of reported cases of HepA virus infection in the U.S. declined 17.3-fold, from 10.4 during 1990 to 1998 to 0.6 during 2007 to 2015. What has been concerning, however, is that the rate increased to 2.8 during 2016 to 2020. “The overall hepatitis A seroprevalence in the United States increased from 38.2% (95% CI, 36.2%-40.1%) during 1976-1980 to 47.3% (95% CI, 45.4%-49.2%) during 2015-March 2020,” the authors wrote. “The prevalence of self-reported hepatitis A vaccination coverage in the United States increased more than 2.5-fold, from 16.3% (95% CI, 15.0%-17.7%) during 1999-2006 to 41.9% (95% CI, 40.2%-43.7%) during 2015-March 2020.”

The researchers concluded that HepA epidemiology in the U.S. changed substantially from 1976 to 2020. “Improved vaccination coverage, especially among adults recommended for vaccination by the Advisory Committee on Immunization Practices [ACIP], is vital to stop current hepatitis A outbreaks associated with person-to-person transmission in the United States and prevent similar future recurrences,” the researchers added.

One dose of single-antigen HepA vaccine has been shown to control outbreaks of HepA, public health officials stated.

The CDC pointed out that HepA virus (HAV) disease disproportionately affects adolescents and young adults, American Indian/Alaska Native and Hispanic racial/ethnic groups, and disadvantaged populations.

From 1996 to 2006, the ACIP made incremental changes in HepA vaccination recommendations to increase coverage for children and persons at high risk for HAV infection. Those changes “eliminated most absolute disparities in HAV disease by age, race/ethnicity, and geographic area with relatively modest ≥1-dose and ≥2-dose vaccine coverage,” the CDC reported in 2016, but it noticed that the proportion of cases had begun to increase. The CDC noted that international travel and the global food economy were big contributors to the outbreaks. More recently, person-to-person transmission has grown as a cause of the infection, with drug users, the homeless, men who have sex with men, those incarcerated, and patients with chronic liver disease being the most vulnerable, according to the CDC.

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