Access to healthcare as an important moderating variable for understanding geography of immunity levels for COVID-19 - preliminary insights from Poland
Background. Underascertainment of COVID-19 burden and uncertainty in estimation of immunity levels is a known and common phenomenon in infectious diseases. We tested to what extent healthcare access (HCA) related supply/demand interfered with registered data on COVID-19 from Poland. Material and methods. We have run a multiple linear regressions model with interactions to explain geographical variability in seroprevalence, hospitalization (on voivodeship: NUTS-2 level) and current (beginning of the 4th wave: 15.09-21.11.2021) case notifications/crude mortality (on poviats: old NUTS-4 level) taking vaccination coverage and cumulative case notifications till so called 3rd wave as predictor variables and supply/demand (HCA) as moderating variables. Results. HCA with interacting terms (mainly demand) explained to the great extent the variance of current incidence and most variance in case of current mortality. HCA (mainly supply) is significantly moderating cumulative case notifications till the 3rd wave explaining the variance across seroprevalence. Conclusions. Seeking causal relations between vaccination or infection gained immunity level and current infection dynamics could be misleading without understanding socio-epidemiological context such as the moderating role of HCA (sensu lato). After quantification, HCA could be incorporated into epidemiological models for better prediction of real disease burden.