Long term Immunogenicity of Single Dose of Live Attenuated Hepatitis A Vaccine in Indian Children — Results of 15-Year Follow-up

Expert consensus and recommendations on the live attenuated hepatitis A vaccine and immunization practices in India

While Hepatitis A Virus (HAV) vaccination in global immunization programs has shown a virtual elimination of the disease within few years of the vaccination program, changing epidemiological landscape in India underscores the need for evidence-based, updated guidance on immunization practices. In May 2024, a panel of 15 distinguished opinion leaders and an organizing committee convened for an intensive, face-to-face advisory board meeting on high burden of HAV infection among adults, increased mortality rate in adolescents, symptomatic presentation in children, and evolving landscape globally and within India. Extensive comparable deliberations on long-term follow-up data from India and data from country of origin advocated immunogenicity, tolerability, and long-term protective effects of single-dose live attenuated HAV vaccine in children. Finally, a consensus was achieved on recognition of increased global attention toward HAV prevention through vaccination coverage. The need for a single dose of live attenuated HAV vaccine was an important outcome of this meeting.

The durability of vaccine-induced protection: an overview

INTRODUCTION

Current vaccines vary widely in both their efficacy against infection and disease, and the durability of the efficacy. Some vaccines provide practically lifelong protection with a single dose, while others provide only limited protection following annual boosters. What variables make vaccine-induced immune responses last? Can breakthroughs in these factors and technologies help us produce vaccines with better protection and fewer doses? The durability of vaccine-induced protection is now a hot area in vaccinology research, especially after COVID-19 vaccines lost their luster. It has fueled discussion on the eventual utility of existing vaccines to society and bolstered the anti-vaxxer camp. To sustain public trust in vaccines, lasting vaccines must be developed.

AREAS COVERED

This review summarizes licensed vaccines' protection. It analyses immunological principles and vaccine and vaccinee parameters that determine longevity of antibodies. The review concludes with challenges and the way forward to improve vaccine durability.

EXPERT OPINION

Despite enormous advances, we still lack essential markers and reliable correlates of lasting protection. Most research has focused on humoral immune responses, but we must also focus on innate, mucosal, and cellular responses - their assessment, correlates, determinants, and novel adjuvants. Suitable vaccine designs and platforms for durable immunity must be found.

Hepatitis A virus infection

Hepatitis A is a vaccine-preventable infection caused by the hepatitis A virus (HAV). Over 150 million new infections of hepatitis A occur annually. HAV causes an acute inflammatory reaction in the liver that usually resolves spontaneously without chronic sequelae. However, up to 20% of patients experience a prolonged or relapsed course and <1% experience acute liver failure. Host factors, such as immunological status, age, pregnancy and underlying hepatic diseases, can affect the severity of disease. Anti-HAV IgG antibodies produced in response to HAV infection persist for life and protect against re-infection; vaccine-induced antibodies against hepatitis A confer long-term protection. The WHO recommends vaccination for individuals at higher risk of infection and/or severe disease in countries with very low and low hepatitis A virus endemicity, and universal childhood vaccination in intermediate endemicity countries. To date, >25 countries worldwide have implemented such programmes, resulting in a reduction in the incidence of HAV infection. Improving hygiene and sanitation, rapid identification of outbreaks and fast and accurate intervention in outbreak control are essential to reducing HAV transmission.