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  • Hepatitis A outbreaks have increasd despite an effective vaccine.
  • While outbreaks have been occurring in recent years, who the outbreaks predominantly affect has changed significantly since the introduction of the vaccine.
  • An effective vaccination program and good hygiene can reduce the transmission of hepatitis A.

The Centers for Disease Control and Prevention (CDC) linked widespread hepatitis A outbreaks to person-to-person transmission in the United States between 2016 and 2020 in a recent Morbidity and Mortality Weekly Report.

Cases of hepatitis A declined after the introduction of an effective vaccine in 1996. However, the CDC’s report shows that there were 37,500 cases between August 1, 2016 and December 31, 2020 with outbreaks happening in 33 states.

The rates of hepatitis A cases have increased dramatically in recent years from under 1 case per 100,000 people in 2016 to over 5 cases per 100,000 people in 2019.

Prior to the introduction of the vaccine, hepatitis A occurred in large endemic outbreaks in the United States. 59,606 cases, the highest annual number on record, were reported in 1971. Historically, most of the cases occurred in the western United States with children ages 2 to 18 making up the majority of cases.

While cases have declined significantly since the introduction of the vaccine, decreasing 97% from 1995 to 2015, recent outbreaks have occurred due to person-to-person transmission. The CDC found the frequency and distribution of hepatitis A cases have changed in the more recent outbreaks.

Who is most affected by the increase in hepatitis A outbreaks?

Children are no longer the primary group affected. The CDC reports 56% of people with hepatitis A also reported drug use and 14% of cases were among people who reported homelessness.

Of 37,553 reported cases, 62% were males, 81% of cases were in white persons, 58% happened in people from 30 to 49 years of age. Of note, people who had previous or current hepatitis B or C cases accounted for between 5% and 30% of cases reported.

Dr. Aniruddh Setya, a pediatric gastroenterology physician and researcher at KIDZ Medical Services in South Florida, believes the recent rise in outbreaks probably has to do with the vaccination status of the most affected groups of people.

He says, “The age group of the currently affected individuals of the outbreak suggests that these individuals were probably not vaccinated.”

A disproportionate number of cases occurred in people who are either experiencing homelessness or use drugs, according to the CDC report.

Why is this population so affected by the increase in Hep A?

Setya says living conditions may impact the populations who are most at risk for hepatitis A.

Hepatitis A is usually transmitted by the fecal-oral route (either via person-to-person contact or consumption of contaminated food or water), he explained. In a resource-rich country like the USA, the people who are living in unsanitary conditions are the most at-risk population.

Setya elaborates on why people who use certain drugs are more affected by hepatitis A than the general population saying, “[Intravenous] drug use causes introduction of the contaminant directly into the bloodstream. It is like directly putting the virus in your blood as opposed to oral route which gives a chance to your natural immune system in the gut wall to fight it and protect you from it.”

What steps can be taken to decrease hepatitis A outbreaks?

The CDC report authors also concluded that improving vaccination coverage in at-risk groups would be key.

“Increased hepatitis A vaccination coverage, through implementation of nontraditional vaccination strategies to reach disproportionately affected populations, along with improved universal and catch-up childhood vaccination, will be necessary to respond to the current hepatitis A outbreaks and prevent similar outbreaks in the future,” they wrote.

A 2020 study published in the American Journal of Public Health found that misinformation about the hepatitis A vaccine could be an issue in getting people protected against the disease.

The authors found instances of vaccine misinformation on Twitter during a hepatitis A outbreak in San Diego from 2016 to 2018 but also found that health officials may be able to combat that misinformation if they responded quickly.

“We came across the issue of vaccine shortage during the hepatitis A outbreak which was in alignment with what public health agencies said,” said study co-author Lourdes Martinez, PhD, in a statement at the time of publication. “But we also came across tweets that said “I just got vaccinated but I’m still scared to go downtown” which suggests they had doubts about its effectiveness.”

“We have proven that vaccination is the most successful measure of safeguarding yourself,” Setya said. He pointed out humans are the only known reservoir of the virus or the only way the virus can replicate.

Aside from getting vaccinated, he recommends practicing good hygiene. “Handwashing is one of the biggest measures of protecting yourself,” he says.

He points out that, “International travel and exposure to foodborne outbreaks and unsanitary conditions were previously the most frequently reported risk factors.”

However, the risk has been reduced because “even resource-limited countries are making the hepatitis A vaccine part of their national immunization programs.”