Vaccination strategies in structured populations under partial immunity and reinfection

Abstract

Optimal protocols of vaccine administration to minimize the effects of infectious diseases depend on a number of variables that admit different degrees of control. Examples include the characteristics of the disease and how it impacts on different groups of individuals as a function of sex, age or socioeconomic status, its transmission mode, or the demographic structure of the affected population. Here we introduce a compartmental model of infection propagation with vaccination and reinfection and analyze the effect that variations on the rates of these two processes have on the progression of the disease and on the number of fatalities. The population is split into two groups to highlight the overall effects on disease caused by different relationships between vaccine administration and various demographic structures. As a practical example, we study COVID-19 dynamics in various countries using real demographic data. The model can be easily applied to any other disease transmitted through direct interaction between infected and susceptible individuals, and any demographic structure, through a suitable estimation of parameter values. Two main conclusions stand out. First, the higher the fraction of reinfected individuals, the higher the likelihood that the disease becomes quasi-endemic. Second, optimal vaccine roll-out depends on demographic structure and disease fatality, so there is no unique vaccination protocol, valid for all countries, that minimizes the effects of a specific disease. Simulations of the general model can be carried out at this interactive webpage [1].

Differences in Trends in Admissions and Outcomes among Patients from a Secondary Hospital in Madrid during the COVID-19 Pandemic: A Hospital-Based Epidemiological Analysis (2020–2022)

“…An interesting point arises regarding vaccination and the subsequent drop in mortality among elderly individuals. Some recent publications have focused on choosing the best vaccination strategy based on certain criteria [ 46 , 47 ]. A protocol should be applied depending on the population structure when the aim is to prevent the spread of an illness, limit the number of deaths, and reduce the impact on health care.…”

“…They demonstrate that different disease characteristics and different population structures may play an important role in the choice of certain vaccination protocols. In the case of Spain, a country included in one of the publications [ 46 ], vaccinating the elderly resulted in a reduction in overall mortality and was probably responsible for the increased number of confirmed cases and admissions among the unvaccinated, younger population.…”

“…The omicron variant and its descendants (B.1.1.529) were identified in November 2021 [ 53 ]. This variant was more transmissible than previous variants, and by January 2022 (sixth wave: from November 2021 to March 2022) it was predominant in Spain [ 46 , 47 ]. This variant affected the population even if they were vaccinated because it was more infectious and could evade their immune responses.…”

Learning from the COVID-19 pandemic: a systematic review of mathematical vaccine prioritization models

“…Many infectious disease models explicitly include vaccine hesitancy by assuming that a proportion of each sub-population cannot be vaccinated. Some models simply assume that this proportion is fixed (Bubar et al, 2021; Gavish and Katriel, 2022; Islam et al, 2021; Li et al, 2022; Luebben et al, 2023; Kadelka et al, 2022; Makhoul et al, 2020; Miura et al, 2021; Moore et al, 2021a; Rodriguez-Maroto et al, 2023; Tatapudi et al, 2021; Walker et al, 2022; Hogan et al, 2021; McBryde et al, 2021; Rahmandad, 2022), while others account for lower hesitancy among older individuals (Liu et al, 2022a; Moghadas et al, 2021; Han et al, 2021; Liu et al, 2022b; Moore et al, 2021b; Zavrakli et al, 2023). Most models in the latter category differentiate hesitancy using a binary age threshold.…”

Vaccination, asymptomatics and public health information in COVID-19

“…The understanding that the susceptible population is heterogeneous, thus making ODE models of the type considered here not completely satisfactory is discussed in [10]. Vaccination strategies and quality of protection are considered in [15,20,24,25]. Particular role of asymptomatics in epidemics dynamics are the main topic in [1,6,9,11,22].…”