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PEP using hepatitis A vaccine can be efficacious
Available data suggest that the vaccine is efficacious post-exposure.
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The current Advisory Committee on Immunization Practices recommendation with respect to post-exposure hepatitis A prophylaxis calls for a single dose of immune globulin as soon as possible, but within two weeks of exposure if at all possible. In cases where the hepatitis A vaccine is also recommended, it can be administered simultaneously with immune globulin.
The current recommendation addresses the use of hepatitis A vaccine alone by saying that the “results of an appropriately designed clinical trial comparing the post-exposure efficacy of vaccine with immune globulin are needed to determine if hepatitis A vaccine without immune globulin can be recommended.”
An ACIP work group was recently formed to review available data with respect to the hepatitis A vaccine regarding age groups, patients with chronic liver disease and other underlying medical conditions.
“We also considered patient characteristics associated with more severe outcomes, response to vaccine and the risk for transmission in scenarios where post-exposure prophylaxis is given in the United States, and we tried to draw on the experience of other countries that use post-exposure vaccine currently,” said Ryan Novak, PhD, epidemiologist of the CDC’s division of viral hepatitis and a member of the ACIP Hepatitis Vaccine Work Group.
Potential benefits
Being able to use the vaccine post-exposure has a number of potential benefits, such as long-term protection, ease of administration, acceptability and availability.
According to Novak, there is currently only one American supplier of immune globulin, and the cost has risen considerably during the past 10 years, making it similar to the cost of the hepatitis A vaccine.
“A single adult dose of immune globulin is now about $20; a pediatric dose of hepatitis A vaccine is about $12 (under government contract), and an adult dose is about $19,” Novak said.
Another benefit is that using hepatitis A vaccine post-exposure would bring practices in this country in line with many other countries that currently provide post-exposure prophylaxis.
The work group discussed a study conducted by Almaty et al in Kazakhstan. The study included 4,524 households or daycare contacts aged between 2 and 40 years. Contacts were exposed to index cases within two weeks after index case symptom onset. The contacts had no history of hepatitis A or receipt of hepatitis A vaccine or immune globulin within the previous six months, chronic liver disease, or contraindications to vaccine or immune globulin. Patients were randomly assigned to receive vaccine or immune globulin within two weeks of index case symptom onset.
Researchers found that hepatitis A vaccine efficacy was similar to that of immune globulin. The risk for hepatitis A among vaccine recipients was never more than 1.5% greater than among immune globulin recipients.
There was no evidence suggesting that vaccine given in the second week post-exposure resulted in lower clinical protection; the study data provided evidence that immune globulin might attenuate clinical illness when given after exposure.
“Looking at clinical endpoints by age, most cases were among children in the study, so that is where we made the most inference; however, the estimates for adults are similar,” Novak said.
Considering the findings of this study, it was the consensus of the work group that there was sufficient evidence to support equivalency of vaccine to immune globulin in both children and adults aged 40 years or younger.
Licensing for children
When the Almaty study was conducted, the hepatitis A vaccine was not licensed for children aged as young as 12 months. However, the work group decided to include children aged 12 to 23 months in the vaccine recommendation because there is no evidence to suggest persistence of maternal antibody past 12 months, and the immunogenicity of the vaccine at 12 months is similar to 24 months.
Currently, the vaccine is licensed from 12 months through the hepatitis A immunization program, and ACIP recommendations include this age group for pre-exposure vaccine use.
Because of the absence of vaccine performance data in people aged older than 40 years and the risk for severe hepatitis A increasing with age, the work group concluded that immune globulin is preferred for patients aged older than 40 years. If immune globulin cannot be obtained, vaccine can be used.
The next populations addressed were people diagnosed with chronic liver disease, immune compromised people and people with other medical conditions. Patients with liver disease or other chronic medical conditions are known to have poor response to vaccine pre-exposure. In addition, patients with chronic liver disease have a higher risk for more severe disease outcomes.
“The work group decided to leave the current recommendations for immune globulin in these groups,” Novak said. Immune globulin should also be used for infants aged younger than 12 months.
The work group also assessed standard of care in other countries. For example, in Canada, vaccine without immune globulin is the preferred method of post-exposure prophylaxis, whereas immune globulin continues to be used for infants and immune-compromised patients.
“Any recommendation that the committee might make about the ability to use vaccine would represent an off-label use, as it is not approved by the FDA for this indication,” Novak said. – by Michelle Stephenson
For more information:
- Novak R. Post-exposure prophylaxis with hepatitis A vaccine. Presented at: the Advisory Committee on Immunization Practices Meeting; Atlanta; June 27-28, 2007.