A string of unexplained hepatitis cases in children has been reported in the U.S. and in other countries. The cause is not yet known, but the top suspect so far is a strain of adenovirus. Contrary to some social media posts, there is no evidence that COVID-19 vaccination is involved. Most of the children are too young to even qualify for the vaccine.
Update, April 5, 2023: Three studies, published together in Nature on March 30, 2023, linked adeno-associated virus 2, or AAV2, to the outbreak of pediatric hepatitis cases in 2022. AAV2 is not known to cause hepatitis and requires the aid of “helper” viruses — often adenoviruses or herpesviruses — to replicate. The studies, from the U.K. and the U.S., suggest that the hepatitis cases were a result of co-infection with AAV2 and other helper viruses in genetically susceptible children. As for why these cases were observed in a cluster in 2022, each of the papers proposes that fewer social interactions during the pandemic may have reduced immunity to these viruses in children, increasing the risk of this type of hepatitis. The studies did not find a link between the hepatitis cases and infection with the coronavirus that causes COVID-19.
In April, the Centers for Disease Control and Prevention and the World Health Organization issued alerts about a number of unusual, severe hepatitis cases in children due to an unknown cause. Across the globe, around 170 cases had been identified as of late April, most of them in the U.K.
Hepatitis is often associated with several well-known hepatitis viruses, but the condition itself refers to inflammation of the liver, which could be due to a variety of causes, including other infections or environmental toxins.
Health authorities are still investigating to understand what is causing the rare hepatitis in these children, but it’s not any of the usual hepatitis viruses. Many, but not all, of the kids have tested positive for an adenovirus. The adenovirus family includes more than 50 different types, which typically cause mild illness in healthy children.
Curiously, though, the type of adenovirus that has been identified in some of the patients, adenovirus 41, has only been known to cause hepatitis in children who are immunocompromised, which isn’t the case here.
Critically, most of the affected children have not been vaccinated for COVID-19, so there is no indication that COVID-19 vaccination could be the cause. Many of the children, in fact, are too young to even be eligible for such vaccination.
Posts on social media have nevertheless suggested that COVID-19 vaccination is behind the unexplained pediatric hepatitis. One even erroneously posits that it could be the Johnson & Johnson COVID-19 vaccine, since that vaccine uses an adenovirus vector design.
“Kids are getting hepatitis. It’s being caused be an adenovirus. J&J had an adenovirus vector. Couldn’t possibly be related,” reads an April 22 tweet from a chiropractor, which was subsequently shared by others on other platforms.
But that reasoning is flawed on multiple counts. First, it fundamentally misunderstands how adenoviral vectors work in the COVID-19 vaccines. The vaccine viruses are modified to no longer be harmful — and they don’t replicate inside cells, so you can’t be infected with the adenovirus from the vaccine. The virus is simply a way to deliver to cells the instructions to make the coronavirus spike protein, which is what the immune system responds to to provide protection.
Second, there’s no indication that any of the kids with hepatitis have received the J&J vaccine. It’s not authorized for use in children in the U.S., and the company confirmed to FactCheck.org that it’s not authorized for kids anywhere in the world.
Third, the specific adenovirus that has been identified in multiple hepatitis cases in children is human adenovirus type 41. The Johnson & Johnson vaccine uses a modified type 26 virus. (The AstraZeneca Oxford COVID-19 vaccine, which also uses a viral vector design, is only authorized for adults in places such as the U.K., and uses a chimpanzee adenovirus.)
To propose a link to the J&J vaccine on this basis is illogical and ignores all available evidence.
Mysterious Hepatitis in Children
In the U.S., the first reports of unusual hepatitis in children occurred in Alabama between October 2021 and February 2022. Nine children, all younger than 6 years old, were treated in the hospital for severe hepatitis. Two kids needed liver transplants, but all children are recovering or have recovered, according to a Morbidity and Mortality Weekly Report published by the CDC on April 29.
Although referred to as a “cluster,” the children came from across the state. All tested negative for hepatitis viruses and SARS-CoV-2, the virus that causes COVID-19, but were positive for adenovirus. For five of the nine kids, it was possible to sequence the virus, which revealed that they were infected specifically with adenovirus type 41. A CDC spokesperson told us that none of the nine children had been vaccinated against COVID-19.
“At this time, we believe adenovirus may be the cause for these reported cases, but other potential environmental and situational factors are still being investigated,” the CDC said in an April 29 statement about the Alabama cluster. “Adenovirus type 41 is not usually known as a cause of hepatitis in otherwise healthy children, and no known epidemiological link or common exposures among these children has been found.”
The CDC issued an alert on April 21 so doctors would be on the lookout for hepatitis in children. Physicians at the University of Alabama at Birmingham said in a press briefing on April 25 that they had not identified any more cases since they issued a statewide alert in February. They added that parents do not need to panic, as these cases are very rare, but people should seek medical attention if a child shows signs of liver disease, such as the yellowing of the skin or eyes, along with the more common symptoms such as diarrhea, vomiting, fever, or coughing and sneezing.
A CDC spokesperson told us that the agency has received additional reports from providers as a result of the nationwide health advisory and was working to determine if any met the current case definition.
Other states, meanwhile, have reported their own potential cases, including Wisconsin, Illinois and North Carolina.
Update, May 7: Due to reports received after issuing its health alert, the CDC said on May 6 that it is now investigating 109 cases among previously healthy children, including five deaths, that occurred in the U.S. over the past seven months. More than half of the children had confirmed adenovirus infections. More than 90% were hospitalized and 14% had liver transplants. It’s possible not all of the cases will ultimately be related to the string of unexplained cases, Dr. Jay Butler, the CDC’s deputy director for infectious diseases, said in a news briefing.
“The children affected are young with a median age of 2 years, which means that most are not eligible to receive the COVID-19 vaccine,” Butler also said. “COVID-19 vaccination is not the cause of these illnesses, and we hope that this information helps clarify some of the speculation circulating online.”
Worldwide, the largest outbreak has been in the U.K., which identified 145 cases this year, through April 29, “predominantly” in children under the age of 5. As in the U.S., children in the U.K. aren’t eligible for COVID-19 vaccination until they turn 5.
The U.K. Health Security Agency wrote in an April 25 update, “There is no link to the coronavirus (COVID-19) vaccine. None of the currently confirmed cases in under 10 year olds in the UK is known to have been vaccinated.”
As of April 21, the WHO reported at least 169 hepatitis cases in children 16 years of age and younger in 11 European countries and the U.S. Adenovirus was detected in “at least 74 cases,” the WHO report said, and “of the number of cases with information on molecular testing, 18 have been identified as F type 41.” In those that were tested, 20 children were positive for SARS-CoV-2 and 19 children were coinfected with SARS-CoV-2 and adenovirus.
The WHO has said there is no evidence that COVID-19 vaccination is related in any way to the hepatitis. “Hypotheses related to side effects from the COVID-19 vaccines are currently not supported as the vast majority of affected children did not receive COVID-19 vaccination,” the agency said in its April 23 disease outbreak report.
In an April 28 live Q&A, WHO officials repeated that there is nothing to support a link to the COVID-19 vaccines, as most of the children with hepatitis haven’t been vaccinated, nor are they eligible to be vaccinated yet, because of their age.
Since so many of the children have tested positive for an adenovirus, many investigators consider the virus a top contender to explain the hepatitis. But even if that’s the case, it’s likely there are other factors involved. Experts remain open to other possibilities as well, as the cause is still very much an open question.
“The leading hypothesis at present is that the hepatitis is linked to adenovirus,” a U.K. technical report from April 25 reads. “There may be a cofactor causing a normal adenovirus to produce a more severe clinical presentation in young children, such as increased susceptibility due to reduced exposure during the pandemic, prior SARS-CoV-2 or other infection, or a yet undiscovered coinfection or toxin. Alternatively, there may have been emergence of a novel adenovirus strain with altered characteristics.”
Similarly, the European CDC wrote in an April 28 risk assessment that “the current leading hypothesis is that a cofactor affecting young children having an adenovirus infection, which would be mild in normal circumstances, triggers a more severe infection or immune-mediated liver damage. Other aetiologies (e.g. other infectious or toxic agents) are still under investigation and have not been excluded but are considered less plausible.”
The WHO outbreak alert noted that adenovirus infection “does not fully explain the severity of the clinical picture,” since infection with adenovirus type 41, “the implicated adenovirus type, has not previously been linked to such a clinical presentation.” Adenoviruses, WHO explains, are quite common, but typically are self-limiting and cause respiratory or gastrointestinal symptoms, or sometimes conjunctivitis, or pink eye.
One possible reason for why children could be more susceptible to adenoviruses now could be because they were exposed to them less over the past several years as people spent more time apart during the pandemic. As a result, kids would have less immunity to adenoviruses.
“Factors such as increased susceptibility amongst young children following a lower level of circulation of adenovirus during the COVID-19 pandemic, the potential emergence of a novel adenovirus, as well as SARS-CoV-2 co-infection, need to be further investigated,” the report said, adding that both the U.K. and the Netherlands have reported increases in community adenovirus infections “following low levels of circulation earlier in the COVID-19 pandemic.”
Regardless of the cause, physicians encourage parents and children to wash their hands and practice good hygiene, which can help avoid the spread of adenoviruses as well as other infectious agents.
Editor’s note: SciCheck’s COVID-19/Vaccination Project is made possible by a grant from the Robert Wood Johnson Foundation. The foundation has no control over FactCheck.org’s editorial decisions, and the views expressed in our articles do not necessarily reflect the views of the foundation. The goal of the project is to increase exposure to accurate information about COVID-19 and vaccines, while decreasing the impact of misinformation.
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