The Long-Term Impact of COVID-19 Non-Pharmaceutical Interventions on Notifiable Infectious Diseases in Poland: A Comprehensive Analysis from 2014-2022

IntroductionThe COVID-19 pandemic prompted widespread implementation of non-pharmaceutical interventions (NPIs) to limit SARS-CoV-2 transmission. These interventions, including lockdowns, face covering, movement restrictions, and school closures, also altered circulation patterns of other pathogens. These measures were enforced on a large scale in Poland beginning in 2020 and persisted through 2022, introducing a rare opportunity to assess broader impacts on other communicable diseases. Previous research frequently addressed short-term alterations in disease incidence, yet knowledge of extended effects remains limited. AimThe study aimed to assess how the pandemic and associated measures changed the incidence of 17 notifiable infectious diseases in Poland from January 2014 to December 2022. The analysis investigated whether NPIs were correlated with immediate declines, sustained decreases, or rebounds in disease activity, with particular attention to changes in disease dynamics across pre-pandemic and pandemic phases, identifying severity of resurgent trends once restrictions were lifted. Materials and MethodsBiweekly case counts for 17 notifiable diseases were collected from the National Institute of Public Health-National Institute of Hygiene, then aggregated into monthly intervals. The study period encompassed five phases: 2014-2018, 2019 (baseline), and each pandemic year (2020, 2021, 2022). Crude annual incidences were calculated and converted to percentage changes, with comparisons between baseline and pandemic periods as well as among individual pandemic years. Seasonality was removed with X13-ARIMA-SEATS, enabling clearer detection of incidence fluctuations. A two-stage negative binomial generalized linear model (GLM) controlled for autocorrelation and potential confounders, producing incidence rate ratios (IRRs) relative to the 2019 reference phase. The analysis evaluated nine NPIs, including school closure, stay-at-home orders, public gathering bans, and an overall stringency index. Spearman correlation coefficients measured associations between the deseasonalized disease time series, COVID-19 case counts, and each of the nine NPIs. ResultsThirteen of the 17 diseases exhibited cumulative declines from 2020 to 2022 when compared to 2014-2019, ranging from 10.48% (syphilis) to 87.63% (whooping cough). The largest single-year drop appeared in 2021 for whooping cough, which showed a 94.56% decrease from 2019. Statistical modeling revealed an IRR of 0.32 (95%CI 0.24-0.42, p<0.001) in 2020 and 0.11 (95%CI 0.08-0.15, p<0.001) in 2021, exhibiting a significant, sustained reduction in incidence. Scarlet fever, chickenpox, and mumps followed a similar pattern, with IRRs persistently below 0.5 throughout at least one pandemic phase. Invasive Streptococcus pneumoniae remained reduced in 2020 (IRR 0.33 [0.24-0.46], p<0.001), yet rebounded in 2022 with an 88.94% rise over 2019. Clostridium difficile diverged from most other diseases, showing a 2.88% increase in 2020 and a jump of over 117% in 2021 compared to 2019, alongside an IRR of 1.84 (1.64-2.07, p<0.001). Noteworthy surges in norovirus (84.5% in 2021 vs. 2019), HIV (63.5% in 2022 vs. 2019), and syphilis (34.92% in 2022 vs. 2019) aligned with relaxation of NPIs. Correlations generally showed strong negative associations between respiratory pathogens and higher NPI stringency, while C. difficile displayed a positive relationship with COVID-19 case counts and several NPIs. These contrasting trends reflected the multifaceted ways that reduced mobility, physical distancing, and masking influenced various modes of disease transmission. ConclusionLong-term observation confirmed that widespread NPIs had a strong suppressive effect on many communicable diseases beyond SARS-CoV-2, particularly those transmitted via respiratory droplets. Several infections rebounded when NPIs were relaxed, indicating potential shifts in susceptibility within the population. Future strategies aiming to balance public health protection with social and economic priorities may benefit from these findings, although additional research is needed to clarify how evolving interventions and changing pathogen transmission patterns influence disease resurgence over extended timeframes.