The role of vaccine in controlling hepatitis A epidemics

Persistence of immunity from 1 year of age after one or two doses of hepatitis A vaccine given to children in Argentina

BACKGROUND

This study was done to determine the immunogenicity of a single dose of hepatitis A vaccine in children, providing needed clinical data on the flexibility of booster administration.

METHODS

Participants had received one dose of inactivated hepatitis A vaccine (Avaxim™ 80 U Pediatric) at 12-23 months of age or two doses of the same vaccine at 12 and 18 months of age prior to enrolment. Anti-hepatitis A antibody concentrations were measured at the first, second, and third year after vaccination. Suspected cases of hepatitis A in participant families were assessed and family socioeconomic data were collected.

RESULTS

A series of 546 participants were enrolled. Of 467 (85.5%) participants completing 3 years of follow-up, 365 had received a single vaccine dose and 94 had received two vaccine doses. Seropositivity (anti-HAV ≥ 10 mIU/mL) at 3 years was 99.7% after one dose and 100% after two doses. At one year, geometric mean concentrations were higher after two doses (1433.9 mIU/mL, 95% confidence interval [CI] 1108-1855) than one (209.7 mIU/mL, 95% CI 190.6-230.6). Geometric mean concentrations decreased in both groups during the study, but remained well above 10 mIU/mL through the third year. The geometric mean of 3-year to one-year anti-hepatitis A concentration ratios was 0.74 (95% CI 0.70-0.79) following one dose and 0.57 (95% CI 0.47-0.70) following two doses. The greatest decrease in geometric mean concentrations occurred during the third year, ie, 21.2% in the one-dose group and 40.8% in the two-dose group. Six participants became seronegative during follow-up and responded strongly to a booster dose. Anti-hepatitis A concentrations increased in 135 children (34.9%) in the second year and 50 (13.7%) in the third year; none lived in a family with a case of hepatitis A. Three confirmed cases of hepatitis A occurred in family members. Participants belonged to a middle-income, urban/suburban population with good sanitation facilities and water supplies.

CONCLUSION

A single dose of hepatitis A vaccine at 12-23 months of age resulted in hepatitis A seropositivity in all but one vaccinee after 3 years. Increased anti-hepatitis A serum concentrations suggested exposure to wild-type hepatitis A virus in this middle-class socioeconomic environment. Continuing surveillance is required to confirm the effectiveness of a single-dose hepatitis A vaccination; however, the results of the first three years are encouraging.

Protective effect of inactivated hepatitis A vaccine against the outbreak of hepatitis A in an open rural community

AIM: To evaluate the protective effect of inactivated hepatitis A vaccine (Healive^®) against hepatitis A outbreak in an emergency vaccination campaign.

METHODS: During an outbreak of hepatitis A in Honghe Town, Xiuzhou District, Jiaxing City, Zhejiang Province, two nonrandomized controlled trials were conducted in September 2006. The first trial was to vaccinate 108 anti-HAV negative individuals with close contacts of the patients from September with 1 dose of an inactivated hepatitis A vaccine, Healive^®. The control group comprised of 115 individuals with close contacts of the patients before September. The second trial was to vaccinate 3365 primary and secondary school students who volunteered to receive a dose of Healive^® and 2572 students who did not receive Healive^® serving as its controls. An epidemiological survey was conducted to evaluate the protective efficacy of the vaccine.

RESULTS: A total of 136 hepatitis A cases were reported during an outbreak that started in June, peaked in August and September, and ended after December of 2006. After a massive vaccination of school children in September, the number of cases declined significantly. No hepatitis A was detected in the 108 vaccinated individuals with close contacts of patients, whereas 4 cases of hepatitis A were found in the controls. The infection rate of hepatitis A was not significantly different in the individuals with close contacts of patients whether or not they received the vaccine (P = 0.122). No hepatitis A was detected in the 3365 students who received the vaccine, four cases of hepatitis A were found in the controls. The infection rate of students with or without vaccination was significantly different in the students who received the vaccine (0/3365 vs 4/2572, P = 0.035). The protective efficacy of the vaccine was 100%.

CONCLUSION: Inactivated hepatitis A vaccine demonstrates a good protective effect against an outbreak of hepatitis A.

Immunogenicity, safety, and interchangeability of two inactivated hepatitis A vaccines in Chilean children

OBJECTIVES

To compare the immunogenicity, safety, and interchangeability of two pediatric hepatitis A vaccines, Avaxim 80U-Pediatric and Havrix 720, in Chilean children.

METHODS

In this randomized trial, 332 hepatitis A virus (HAV) seronegative children from 1 to 15 years of age received two doses of Avaxim, two doses of Havrix, or Havrix followed by Avaxim, 6 months apart. Anti-HAV antibody titers were measured before and 14 days after the first dose of vaccine, and before and 28 days after the second dose of vaccine. Immediate reactions were monitored; reactogenicity was evaluated from parental reports.

RESULTS

Seroconversion rates after the first vaccination were 99.4% and 100% for Avaxim and Havrix, respectively. Anti-HAV geometric mean concentrations (GMCs) were 138 mIU/ml for Havrix (95% confidence interval (CI): 120; 159) and 311 mIU/ml for Avaxim (95% CI: 274; 353). GMCs increased to 4008 mIU/ml after two doses of Havrix, 8537 mIU/ml following two doses of Avaxim, and 7144 mIU/ml in children who received Havrix with Avaxim as the second dose. Following the first injection, 36% of subjects given Avaxim and 44% given Havrix reported local reactions; 38% of subjects in the Avaxim group and 40% in the Havrix group reported systemic reactions related to vaccination. Solicited reactions were less frequent after the second dose of Avaxim or Havrix, occurring in 27% to 37% of subjects.

CONCLUSIONS

No significant difference in seroconversion rates was seen 14 days after a single dose of vaccine. A two-dose schedule with either vaccine or with Havrix/Avaxim provided a strong booster response. Both vaccines were well tolerated and can be recommended for routine vaccination of Chilean children. Avaxim 80 may be used to complete a vaccine schedule begun with Havrix 720.

[Hepatitis A outbreak in a day care center and household transmission]

BACKGROUND

An outbreak of hepatitis A occurred in a day care center in Madrid between October 2002 and February 2003 and spread to the children's families.

PATIENTS AND METHODS

We performed a descriptive study of this outbreak and of the control measures adopted.

RESULTS

The outbreak affected 23 people: eight children aged 1-3 years (attack rate= 8.7 %), two staff members (attack rate=10.5 %), and 13 household contacts. Of the 23 cases, 17 were confirmed by serology and eight patients were hospitalized. The control measures were: (i) increasing general hygiene measures in the home and school and, in particular, those concerning diaper changing by staff, and (ii) vaccination of all pupils aged more than one year (92 children), staff members (16 adults) and family contacts of affected individuals. After vaccination, the epidemic curve showed intrafamilial transmission exclusively. Cases among familial contacts affected adults in contact with asymptomatic children.

CONCLUSIONS

Vaccination was effective in controlling the epidemic outbreak within the day care center. However, when outbreaks occur, vaccination should be prescribed to close contacts of all the children, whether symptomatic or not, especially parents and siblings. The recommendation that day care center workers undergo vaccination on taking up their posts should be put into practice, since vaccination is not systematically performed. General vaccination would be the most effective measure for preventing outbreaks in educational centers.

Prevention of hepatitis A by vaccination

Inactivated hepatitis A vaccines have been available for more than a decade. Characteristics of the vaccines, comparative data among different formulations and the possibility of combination and association with other vaccines are reviewed in this article. Hepatitis A vaccines show high immunogenicity with different schedules and associations, induce long-term protection irrespective of timing of booster dose, and present an excellent safety profile. Pre-exposure efficacy has been demonstrated in large trials and postexposure protection has been described in family contacts of acute cases. The recommendations for the use of hepatitis A vaccines for immunisation campaigns and for targeted groups, such as travellers and people at risk for occupational and iatrogenic exposure or lifestyle behaviours, are discussed. Aspects related to economic analysis of vaccination strategies are also considered.