Modeling hepatitis A epidemiological profiles and estimating the pediatric vaccination threshold in the Russian Federation

Abstract

Background: To combat the hesitancy towards implementing a hepatitis A universal mass vaccination (UMV) strategy and to provide healthcare authorities with a comprehensive analysis of the potential outcomes and benefits of the implementation of such a vaccination program, we projected HAV seroprevalence and incidence rates in the total population of the Russian Federation and estimated the pediatric vaccination threshold required to achieve an incidence level of less than 1 case per 100,000 using a new mathematical model.

Methods: A dynamic age-structured SEIRV (susceptible-exposed-infectious-recovered-vaccinated) compartmental model was developed and calibrated using demographic, seroprevalence, vaccination, and epidemiological data from different regions of the Russian Federation. This model was used to project various epidemiological measures.

Results: The projected national average age at the midpoint of population immunity increases from 40 years old in 2020 to 50 years old in 2036 and is shifted even further to the age of 70 years in some regions of the country. An increase of varying magnitude in the incidence of symptomatic HAV infections is predicted for all study regions and for the Russian Federation as a whole between 2028 and 2032, if the HAV vaccination coverage level remains at the level of 2022. The national average vaccination coverage level required to achieve a symptomatic HAV incidence rate below 1 case per 100,000 by 2032 was calculated to be 69.8% if children aged 1-6 years are vaccinated following the implementation of a UMV program or 34.8% if immunization is expanded to children aged 1-17 years.

Conclusion: The developed model provides insights into a further decline of herd immunity to HAV against the background of ongoing viral transmission. The current favorable situation regarding hepatitis A morbidity is projected to be replaced by an increase in incidence rates if vaccination coverage remains at the current levels. The obtained results support the introduction of a hepatitis A UMV strategy in the Russian Federation.

Keywords: HAV; hepatitis A; hepatitis A vaccination; herd immunity; mathematical model.

Figure 1

Comparison of the dynamics of total population size in the study regions and in the Russian Federation as a whole in 2021–2036 according to the model of this study (red area) and based on data from Rosstat (blue area), these projections have high similarity (overlapping areas are shown in purple).

Figure 2

Model-projected age-specific HAV prevalence in the study regions of the Russian Federation (A–H) and in the country as a whole (I). Current HAV seroprevalence based on data from the 2020 serosurvey is shown as dotted curves. Model-projected HAV seroprevalence data are shown as solid lines in dark blue for 2026, medium blue for 2031, and light blue for 2036. The 50% HAV seroprevalence level is shown as a black solid line.

Figure 3

Projected dynamics of symptomatic HAV infection incidence rates in the study regions and in the Russian Federation as a whole. The blue areas depict the number of cases per 100,000 persons per year, with inaccuracy related to approximation and demographic models confidence interval.

Figure 4

Projected dynamics of symptomatic HAV infection incidence rates according to different scenarios. Medium blue areas depict Scenario 0, light blue areas depict Scenario 1, dark blue areas depict Scenario 2, diagonally hatched areas depict Scenario 3, and vertically hatched areas depict Scenario 4.

Figure 5

Changes in age-specific HAV seroprevalence rates projected based on Scenario 3: vaccination of children aged 1–6 years with vaccination rates sufficient to achieve an incidence rate below 1 case per 100,000 by 2032. The 50% HAV seroprevalence level is shown as a black solid line.

Figure 6

Changes in age-specific HAV seroprevalence rates projected based on Scenario 4: vaccination of children aged 1–17 years with vaccination rates sufficient to achieve an incidence rate below 1 case per 100,000 by 2032. The 50% HAV seroprevalence level is shown as a black solid line.