CHAPTER 16
Vaccines for viral hepatitides
Hepatitis A vaccination
Introduction
Hepatitis A is a serious liver disease caused by the hepatitis A virus (HAV). It is usually spread by close personal contact or by eating or drinking contaminated food or water. Humans are the only known reservoir for HAV; hence universal vaccination could potentially lead to eradication of this disease.
Pharmacology
HAV vaccines that are currently available include formalin-inactivated vaccines with and without aluminium hydroxide an adjuvant, live attenuated vaccines, and combination vaccines for HAV with hepatitis B (Twinrix) and with typhoid (Hepatyrix). The inactivated vaccines (HAVRIX and VAQTA) and combination vaccines are the only agents currently approved for use in the United States.
Mechanism of action
Inactivated virus vaccine which offers active immunization against HAV infection.
Indications for vaccination
It is recommended that all children be vaccinated against HAV between their first and second birthdays (12 through 23 months of age) In addition, vaccine should be given to children and adolescents 2 through 18 years of age who live in states or communities where routine vaccination has been implemented because of high disease incidence. Otherwise, vaccine may be administered to children 1 year of age or older whose parents wish to protection them from HAV infection.
All unvaccinated adults at risk for infection should receive immunization as well. High-risk groups include men who have sex with men, injection drug users, persons with chronic liver disease, and persons who are treated with clotting factor concentrates. Additionally, those who work with HAV-infected primates or who work with HAV in research laboratories should be vaccinated, as should anyone 1 year of age and older traveling to or working in countries with high or intermediate prevalence of HAV, such as those located in Central or South America, Mexico, Asia (except Japan), Africa, and eastern Europe.
Others at higher risk of infection include members of households planning to adopt a child, or care for a newly arriving adopted child, from a country where hepatitis A is common,unvaccinated children or adolescents in communities where outbreaks of hepatitis A are occurring, and unvaccinated people who have been exposed to hepatitis A virus. The Advisory Committee on Immunization Practices (ACIP) of the Centers for Disease Control and Prevention (CDC) has also recommended HAV vaccination of adults with HIV infection and in close family contacts of index cases.
Dosing and administration
HAVRIX
Primary immunization in children and adolescents (12 months through 18 years): single dose of 720 EL.U, in 0.5 mL and a booster dose (720 EL.U in 0.5 mL) any time between 6 and 12 months later.
Adults: single dose of 1440 EL.U in 1 mL and a booster dose (1440 EL.U in 1 mL) anytime between 6 and 12 months later.
VAQTA
Primary immunization in children and adolescents (12 months through 18 years): single 0.5 mL (~25 U) dose and a booster dose of 0.5 mL (~25 U) 6 to 18 months later.
Adults 19 and older: single 1.0 mL (~50 U) dose and a booster of 1.0 mL (~50 U) 6 to 18 months later.
Note
When used for primary immunization, the vaccine should be given 1 month (at least 2 weeks) prior to expected HAV exposure. Some protection may still result if the vaccine is given on or closer to the potential exposure date. When used prior to an international adoption, the vaccination series should begin when adoption is being planned, but ideally ≥2 weeks prior to expected arrival of adoptee. When used for post exposure prophylaxis, the vaccine should be given as soon as possible. Vaccines may not be effective if administered during periods of altered immune competence (CDC, 2011).
Co-administration of vaccines: The inactivated hepatitis A vaccine can be given concurrently with the other pediatric vaccines as well as with pneumococcus, typhoid, cholera, Japanese encephalitis, rabies, or yellow fever vaccines without compromising the immunogenicity or safety. The injections should be given at different sites. Preterm infants should be vaccinated at the same chronological age as full-term infants (CDC, 2011).
Administration
Vaccines should be administered intramuscularly; the deltoid is the preferred site in adults while the vastus lateralis (anterolateral thigh) is preferred in infants.
Adverse effects
Mild adverse effects include soreness at the injection site (about 1 out of 2 adults, and up to 1 out of 6 children), headache (about 1 out of 6 adults and 1 out of 25 children), loss of appetite (about 1 out of 12 children), and fatigue (about 1 out of 14 adults).
Serious allergic reaction or anaphylaxis is rare but does occur, and epinephrine should always be available for immediate use where vaccine is administered. Although serious adverse events such as Guillain-Barré syndrome, multiple sclerosis, encephalitis, elevated liver biochemical tests, jaundice and idiopathic thrombocytopenic purpura have been occasionally reported, their relationship to vaccination is unclear.
Contraindications
Vaccine should not be administered to persons with known hypersensitivity to hepatitis A vaccine or any component of the formulation. All hepatitis A vaccines contain alum, and some hepatitis A vaccines contain 2-phenoxyethanol. Anyone who is moderately or severely ill at the time the shot is scheduled should defer vaccination until recover, while those with a mild illness can usually receive the vaccine. Hepatitis A vaccine is not licensed for children younger than 1 year of age.
Clinical effectiveness
The immunogenicity of the vaccine is defined as an antibody concentration of >20 mIU/mL measured by ELISA, and is nearly 100% and long-lasting. Thus, there is no evidence that a hepatitis A booster vaccination after a full primary vaccination is needed in healthy individuals. Certain lots of VAQTA were recalled in 2001 due to low antigen count and inadequate protection. The individuals who received this vaccine may be tested for development of immunity. Due to the long incubation period for hepatitis A (15–50 days), immunization may not prevent infection in those with unrecognized hepatitis A infection. Patients with advanced liver disease may not have a similar response rate and hence vaccination in patients with cirrhosis should be carried out at the earliest possible stage in the course of their disease.
Special considerations
Missed dose
In case of a missed dose, the second dose can be given without restarting the series.
Serologic testing before vaccination
As per CDC, testing of children is not indicated because of the low prevalence of infection in this age group. For adults, the decision is individualized and will be most cost-effective in adults who are from geographic areas that have a high or intermediate endemicity of HAV and in groups that have a high prevalence of infection (e.g., injection drug users and adults older than 40 years).
Post vaccination testing:
Post vaccination testing is not required because of the high rate of vaccine response among healthy adults and children.
Post exposure prophylaxis
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