Modeling the Risk of Airborne Transmission of Respiratory Viruses in Microgravity

Airborne transmission is the most efficient and widespread route of viral spread, posing a significant challenge in controlling major infectious diseases such as COVID-19 and influenza. In microgravity environment, such as the International Space Station (ISS), this mode of transmission requires heightened vigilance and preventive measures due to the prolonged suspension of virus-laden particles, which increases the risk of infection. Using the COVID Airborne Risk Assessment (CARA) tool, we assess the risk of airborne transmission of respiratory viruses in microgravity by simulating the emission, dispersion, and inhalation of virus-laden particles. Our findings show that the unique conditions of microgravity allow these particles to remain airborne for significantly longer periods compared to Earth, leading to a 286-fold increase in virus concentration in the air, resulting in nearly twice the probability of infection for a susceptible host. We also evaluated the effectiveness of preventive measures, and found that facemasks can reduce the risk by up to 23% while continuous HEPA filtration at five air changes per hour proves crucial for managing air quality and minimizing infection risks by reducing airborne virus concentration at 99.79%. However, when simulated the infection risk by accounting the spaceflight-induced immune suppression, we found that the infection probability increased by 12% in the condition that viral load in infected host increase for 8-fold and absence of protective measures. Although facemasks and air filtration help mitigate the risk, their effectiveness diminishes when the viral load carrying by host is high. Enhancing host immunity through vaccination or other interventions is vital, potentially reducing infection probability by up to 14.17% when combined with HEPA filtration. These findings highlight the need for robust mitigation strategies to safeguard the health of astronauts against airborne pathogens during future space missions.