Philip J. Provost

A Controlled Trial of a Formalin-Inactivated Hepatitis A Vaccine in Healthy Children

BACKGROUND Although inactivated hepatitis A vaccine is known to be well tolerated and immunogenic in healthy children and adults, its efficacy has yet to be established. METHODS To evaluate the efficacy of the hepatitis A vaccine in protecting against clinically apparent disease, we conducted a double-blind, placebo-controlled trial in an Hasidic Jewish community in upstate New York that has had recurrent outbreaks of hepatitis A. At the beginning of a summer outbreak, 1037 healthy seronegative children 2 to 16 years of age were randomly assigned to receive one intramuscular injection of a highly purified, formalin-inactivated hepatitis A vaccine or placebo. A case was defined by the presence of typical signs and symptoms, a diagnostic increase in IgM antibody to hepatitis A, and a serum concentration of alanine aminotransferase at least twice the upper limit of normal. Cases occurring greater than or equal to 50 days after the injection were included in the evaluation of efficacy. The children were followed for a mean of 103 days. RESULTS A total of 519 children received vaccine, and 518 received placebo. The vaccine was well tolerated, with no serious adverse reactions. From day 50 after the injection, 25 cases of clinically apparent hepatitis A occurred in the placebo group and none in the vaccine group (P less than 0.001), confirming that the vaccine had 100 percent protective efficacy. Before day 21, seven cases occurred in the vaccine group and three cases in the placebo group. After that time, there were no cases among vaccine recipients and 34 cases among placebo recipients. CONCLUSIONS The inactivated purified hepatitis A vaccine that we tested is well tolerated, and a single dose is highly protective against clinically apparent hepatitis A.

Propagation of Human Hepatitis A Virus in Cell Culture in Vitro

Summary Human hepatitis A virus was reliably and repeatedly propagated in primary explant cell cultures of marmoset livers and in the normal fetal rhesus kidney cell line (FRhK6). Identity of virus was established in immunofluorescence, immunofluorescence blockade, serum neutralization, immune adherence, radioimmunoassay, immune electron microscopy, and marmoset inoculation tests. The virus propagated to greatest extent in FRhK6 cells. No cytopathology was observed. These studies represent the first reliable propagation of human hepatitis A virus in vitro and point the way to the eventual means for detection and quantification of live virus in vitro and of production in cell culture of virus for diagnostic antigen and vaccine preparation.

Modified cases of chickenpox after varicella vaccination : correlation of protection with antibody response

Four thousand forty-two healthy children and adolescents, ages 12 months to 17 years, were vaccinated with a single dose of live attenuated varicella vaccine (VARIVAX®; Merck Sharp and Dohme Research Laboratories) containing ∼1000 to 1625 plaque-forming units/dose during clinical trials conducted from 1987 to 1989. Clinical follow-up of vaccinees revealed that 2.1 and 2.4% of vaccinees developed modified cases of varicella in the first and second years, respectively, after vaccination. Most of those who developed varicella postvaccination had an attenuated illness, characterized by fewer lesions and a lower incidence of fever (≥100°F, oral) than after natural infection. The likelihood of developing varicella postvaccination decreased (P < 0.0001) as the 6-week postvaccination glycoprotein-based enzyme-linked immunosorbent assay titer increased. In addition the number of lesions in these cases tended to decrease (P = 0.07 for Year 1 and P = 0.02 for Year 2) as the 6-week glycoprotein-based enzyme-linked immunosorbent assay titer increased. Thus the 6-week postvaccination glycoprotein-based enzyme-linked immunosorbent assay titer can be used as a surrogate marker for protection from natural disease.

Specific Immune Adherence Assay for Human Hepatitis A Antibody. Application to Diagnostic and Epidemiologic Investigations

Summary A specific immune adherence (IA) test for hepatitis A antibody in human serum was described employing liver extract of marmosets infected with CR326 strain human hepatitis A virus. Persons with hepatitis A, but not hepatitis B, developed hepatitis A IA antibody soon after onset of the acute illness and this persisted thereafter. There was very close agreement in the tests for human hepatitis A immune adherence, complement fixing (CF) and neutralizing antibodies. IA antibodies appeared to develop somewhat later than CF or neutralizing antibody. A limited epidemiologic study of a family outbreak of hepatitis A and B in Costa Rica showed simultaneous occurrence of the two diseases and was supportive of the concept that susceptible persons in a country with high hepatitis A prevalence generally acquire their infections at an early age and are immune thereafter. Most persons of high socioeconomic level in an area of low hepatitis A incidence may proceed to adulthood without experience with hepatitis A. Persons of low socioeconomic level, however, such as commercial blood bank donors and prisoners, show high incidence of hepatitis A antibody. Hepatitis IA and CF antibodies persisted in human subjects for at least 7 hr after hepatitis A virus infection. Captive chimpanzees and grivet and rhesus monkeys, not given hepatitis A virus, showed evidence of previous experience with human hepatitis A or an antigenically related virus based on tests for hepatitis A antibody. Other subhuman primates, rodents, and swine, not given hepatitis A virus, were without hepatitis A antibody. The IA test provides an excellent tool for diagnostic and epidemiologic investigations of hepatitis A and should be of considerable value to detect hepatitis A virus in attempts to propagate the virus in cell culture. There was considerable difference in hepatitis A IA antibody content of different lots of commercial human immune globulin, though the majority titered 1:4000 or 1:8000.

Antibody assays suitable for assessing immune responses to live varicella vaccine

An enzyme-linked immunosorbent assay for antibodies to varicella-zoster virus (VZV), using purified viral glycoproteins as antigen (gpELISA), was compared with other assays for measuring vaccine-induced antibody responses. The gpELISA was more sensitive than conventional assays, proved highly specific for VZV and agreed well with an assay for neutralizing antibody activity. It was successfully applied to large-scale testing of live varicella vaccine in humans.

Physical, chemical, and morphologic dimensions of human hepatitis. A virus strain CR326

Summary CR326 human hepatitis A virus purified by isopycnic banding from infected marmoset sera was shown to consist of 27 nm spherical particles on electron microscopic examination. The particles were identified as hepatitis A virus by tests for infectivity and by specific neutralization of infectivity with convalescent human hepatitis A serum. Also, identical 27 nm viruses in liver extracts gave specific reactions with hepatitis A antisera when tested by immune electron microscopy. The buoyant density of the virus in CsCl was 1.34 and it was heat (60°), ether and acid stable but was destroyed by heat (100°), formalin (1:4000) and ultraviolet irradiation. Electron microscopic studies of sections of infected marmoset liver showed intracytoplasmic virus particles, usually in vesicles. Presumptive findings for RNA, together with the intracytoplasmic location of the virus, indicated the virus to be of RNA-type. The attributes of the virus indicate it is closely related to the entero-virus family and not to hepatitis B virus. The authors are grateful to F. Banker, P. Giesa, L. Hoover, W. Fisher, M. Johnston, C. Dennis and R. Roehm for excellent technical assistance. Drs. A. Tytell and A. Klink gave important technical advice.

Worldwide experience with the CR326F-derived inactivated hepatitis A virus vaccine in pediatric and adult populations: an overview.

The worldwide experience to date with VAQTA, a highly purified formalin-inactivated hepatitis A vaccine containing alum-adjuvant, is reviewed. No serious adverse experience related to vaccination has been reported. The vaccine has proven highly immunogenic, with seroconversion detectable after a single dose in 90-99% of children 2-16 years old, and of adults under 77 kg (170 lb) body weight. There is a trend toward lower one-dose seroconversion rates with increasing age and with weight > 77 kg. Early seroconversion in the latter groups may require two 25-unit doses given 2, 4 or 8 weeks apart, or a higher priming dose. Seroconversion induced by this vaccine has been shown to signify protection from clinical hepatitis A disease. The few vaccines whose titers have waned to borderline levels responded anamnestically to a booster, suggesting that the vaccine induces an immune memory response and should provide long-term protection.

An inactivated hepatitis A virus vaccine prepared from infected marmoset liver.

Summary Human hepatitis A virus, partially purified from the liver of a rufiventer marmoset infected with CR326 strain virus, was inactivated with formalin and was shown to be highly potent in stimulating homologous antibody in marmosets when administered subcutaneously at bi-weekly intervals in eight divided doses. The vaccine was shown to prevent hepatitis A in all marmosets when challenged with live hepatitis A virus in a controlled study.

Etiologic relationship of marmoset-propagated CR326 hepatitis A virus to hepatitis in man.

Summary Studies were conducted to define the etiologic relationship of CR326 hepatitis virus recovered in marmosets to hepatitis A in man. CR326 virus exhibited physical-chemical properties considered characteristic of human hepatitis A virus, viz, small size and heat, ether and acid stability. A serum neutralization test carried out with CR326 virus in S. mystax marmosets is described and the factors influencing the results are given. Tests of paired sera from 8 cases of hepatitis A and 2 cases of hepatitis B were carried out including coded paired sera from 3 human subjects given MS-1 strain hepatitis A and 1 given MS-2 strain hepatitis B virus of human source. All subjects with hepatitis A developed antibody that neutralized CR326 virus; there was no such antibody response in persons with hepatitis B. All of 3 samples of human immune globulin neutralized the CR326 agent. Neutralization was highly effective since marmosets given the neutralized virus remained susceptible to reinfection with the agent; by contrast recovered animals that had been given non-neutralized virus were immune to reinfection. All evidences to establish the relationship of CR326 virus to human hepatitis A are summarized.

Safety, tolerability, and immunogenicity of two regimens of Oka/Merck varicella vaccine (Varivax®) in healthy adolescents and adults

A multicenter clinical trial was conducted among 757 healthy adolescents and adults, 13-54 years, to compare two regimens of Oka/Merck varicella vaccine with respect to safety, tolerability, and immunogenicity. Participants were randomized to receive two injections of vaccine either four or eight weeks apart and were followed for clinical reactions and serologic response. The two vaccine regimens were equally well tolerated. The seroconversion rates (gpELISA) four weeks after injection 1 and 2 were 72 and 99%, respectively, for those who received vaccine four weeks apart and 78 and 99%, respectively, for those who received vaccine eight weeks apart. The differences in seroconversion rates were not statistically significant. However, delaying the second dose to eight weeks resulted in a higher antibody titer one month after the second injection. Administration of a two-dose regimen of varicella vaccine to susceptible adolescents and adults is well tolerated and highly immunogenic.