2 Estimating Spatially Disaggregated Probability of Severe COVID-19 and the Impact of Handwashing Interventions: The Case of Zimbabwe

# Introduction

The coronavirus pandemic (SARS-CoV-2) has affected 220 countries around the world, with over 5.4 million recorded deaths as of December 2021 (JHU, 2021). In Zimbabwe, there have been just under 5,000 recorded deaths following multiple waves (JHU, 2022). The severity of COVID-19 disease varies substantially between individuals, with some infections being asymptomatic while others are fatal. Research studies have identified a number of risk factors for severe disease, which include older age, smoking and underlying comorbidities including <mark>hypertension, diabetes, cardiovascular disease and chronic respiratory disease (</mark> Elmore _et al._ , 2020; Q. Ma _et al._ , 2020; Ou _et al._ , 2020; Wu and McGoogan, 2020; Hu and Wang, 2021).

Handwashing is widely understood to modify risk of respiratory illness as <mark>hands have been known to harbor viral respiratory pathogens (</mark> Gwaltney, 1978; Ansari _et al._ , 1991; Weber and Stilianakis, 2008 <mark>). This happens when hands come into contact with contaminated fomites (environmental surfaces) or through a person-to-person contact with a disease carrier who sheds the respiratory pathogens through their nose or mouth (</mark> Hendley, Wenzel and Gwaltney, 1973; Brady, Evans and Cuartas, 1990 <mark>). Transmission occurs following contact between hands and nasal mucosa or mouth of the new host.</mark> There are at least two channels through which handwashing can theoretically have an impact on reducing the number of severe COVID-19 cases in the population.

The more direct pathway is by reducing transmission of the SARS-CoV-2 virus itself. Health authorities have established that the main transmission routes for SARS-CoV-2 are via either respiratory droplets, inhaled directly by a susceptible individual or through bodily contact, or via an infected surface or fomite (such as door handles or other frequently touched surfaces) (van Doremalen _et al._ , 2020; WHO, 2020). For this reason, handwashing will likely have an impact on transmission of SARS-CoV-2 virus. Hand-washing has been encouraged during the pandemic to reduce the likelihood of spreading the infection from one individual to another (WHO, 2020). There have been more recent efforts to quantify (Talic, 2021) and determine the extent to which both hand-washing facility access (Zvobgo and Do, 2020) and handwashing behavior (Meda _et al._ , 2020, 2020; Yang, 2020; Hirose _et al._ , 2021) could impact the transmission of SARS-CoV-2. However, epidemiological modeling that sought to incorporate handwashing scenarios in predicting disease outcomes in the population have had to make assumptions to quantify the impact of handwashing on transmission reduction (Winskill _et al._ , 2020).

The second, more indirect pathway for handwashing in reducing prevalence of severe COVID-19 is via its impact on reducing other respiratory infections. Reducing transmission and incidence of other respiratory illnesses would reduce prevalence of a risk factor for developing severe COVID19 (Udwadia et al., 2020, Ma et al, Gao et al., 2021; Hu & Wang, 2021; C. Ma et al., 2020; Ou et al., 2020). <mark>A large body of e</mark> mpirical studies in household and community settings have demonstrated the effectiveness of hand washing in reducing other respiratory illnesses around the