COVID-19 pandemic: Impact of lockdown, contact and non-contact transmissions on infection dynamics

Shovonlal Roy

Non-contact transmission and basic reproduction number Basic reproduction number (R 0 ), which is usually defined as the average number of new infections caused by a single infected individual in the susceptible population, depends on the transmission routes and rates. For the SEIR model under investigation, R 0 was calculated from the next-generation matrix [9] . The magnitude of R 0 obtained with person-to-person contact as the only route of transmission, appears to be an underestimation when non-contact transmission is active (Fig. 1 ). If the relative contribution of non-contact transmission is very small, changes in R 0 is generally negligible. But R 0 increases sharply with the relative contribution of non-contact transmission (Fig. 1) . For example, whilst a 50% relative contribution of non-contact transmission increases R 0 by 15-35%, a 150% relative contribution can double it (depending on the nature of infection). Since in the case of COVID-19 the contribution of non-contact transmission is unknown, it is uncertain as to what extent R 0 will spike if no action is taken to reduce this route of transmission.