Access to healthcare as an important moderating variable for understanding geography of immunity levels for COVID-19 - preliminary insights from Poland

BackgroundBiases in COVID-19 burden and uncertainty in estimation of the corresponding epidemiologic indexes is a known and common phenomenon in infectious diseases. We investigated to what extent healthcare access (HCA) related supply/demand interfered with registered data on COVID-19 in Poland. Material and methodsWe run a multiple linear regression model with interactions to explain geographic variation in seroprevalence, hospitalizations (on voivodeship - NUTS-2 level) and current (beginning of the 4th wave - 15.09-21.11.2021) case notifications/crude mortality (on poviat - old NUTS-4 level). We took vaccination coverage and cumulative case notifications up to the so called 3rd wave as predictor variables and supply/demand (HCA) as moderating variables. ResultsHCA with interacting terms (mainly demand) explained to the great extent the variance of current incidence and most variance of current mortality. HCA (mainly supply) is significantly moderating cumulative case notifications till the 3rd wave explaining the variance in seroprevalence and hospitalization. ConclusionsSeeking causal relations between vaccination-or infection-gained immunity level and current infection dynamics could be misleading without understanding socio-epidemiologic context such as the moderating role of HCA (sensu lato). After quantification, HCA could be incorporated into epidemiologic models for improved prediction of real disease burden.