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Learning Objectives for this Presentation:
By the end of the presentation participants will be able to evaluate a) nationwide immunization versus current regional strategy and b) importance of age at immunization by comparing vaccination of 2 year olds versus hypothetical immunization of 12 year olds, upon future HAV incidence in the US.
Background:
A dynamic model of hepatitis A (HAV) transmission was designed to evaluate the impact of different immunization strategies on HAV disease in the US.
Methods:
The dynamic compartmental model describes the flow of hosts between different HAV ‘infectivity stages'. It is stratified by age and geographic regions as defined by the ACIP 1999 recommendations. The model accounts for herd immunity and HAV importation, using an age-dependent force of infection varying over time with the number of infectives in the population.
Results:
Our dynamic model predicts that vaccination of 2 year olds induces strong herd immunity effects. It also predicts a plateauing and potential slow increase in HAV disease if the current regional strategy is continued, most likely due to an increasing pool of susceptibles in non-vaccinated US states, as well as continued HAV importation. When compared to current regional ACIP 1999 strategy, nationwide routine immunization of 2 year olds would reduce the proportion of HAV cases by about 40% in 2002-2029 (~ 137,000 cases) while hypothetical nationwide immunization of 12 year olds would result in an 18 % increase of HAV cases predicted with the current strategy, demonstrating the great importance of creating herd immunity to lower the HAV incidence in US.
Conclusions:
The model predicts that immunization at 2 years of age provides strong herd immunity, which is shown to be a crucial aspect for lowering the HAV incidence in the US. Nationwide HAV vaccination as early in life as possible would be the most effective vaccination strategy in the US.
See more of E1 - Childhood Hepatitis A Epidemiology and Prevention
See more of The 2005 National Viral Hepatitis Prevention Conference