A second wave of COVID-19 could be avoided by maintaining social distances and the use of masks

Individual behavior has a significant effect on preventing a large second wave of COVID-19 infections. In fact, maintaining social distancing and other interventions, such as the use of masks and hand hygiene, could eliminate the need for future confinement, according to a model developed by the Institute of Global Health of Barcelona (ISGlobal), a centre promoted by the "la Caixa" Foundation. The findings, published in Nature Human Behavior, also show that, in countries that have not yet reached the peak of active cases, confinements should be maintained for at least 60 days and deconfinement should be gradual to reduce the risk of second waves.

Several countries that initially imposed strict containment measures to limit the spread of SARS-CoV-2 are in the process of lifting them. However, how and when to ease restrictions is a difficult decision: a delicate balance between the need to revive the economy and the risk of a second wave of infection that could overwhelm health systems. "The problem is that assessing this risk is difficult, given the lack of reliable information on the actual number of people infected or the degree of immunity developed among the population," explains Xavier Rodó, head of ISGlobal's Climate and Health program. In this study, Rodó's team presents projections based on a model that divides the population into seven groups: susceptible, quarantined, exposed, undetected infectious, reported infectious and confined, recovered, and dead. It also allows to simulate both the degree of confinement of the population and the different strategies after confinement.

"Our model is different because it considers the return of the confined persons to the susceptible population to estimate the effect of decontamination, and includes people's behaviors and risk perception as modulating factors," explains Xavier Rodó. "This model may be particularly useful for countries where the peak of cases has not yet been reached, such as those in the southern hemisphere. It would allow us to evaluate control policies and minimize the number of cases and deaths caused by the virus", explains Leonardo López, co-author of the study and also a researcher at ISGlobal.

The use of masks, hand hygiene and staying home mandates have already shown benefits. The objective of this study was to quantitatively evaluate their relevance as containment strategies. The results clearly show that the duration of the first containment will affect the timing and magnitude of subsequent waves, and that gradual de-containment strategies always result in fewer infections and deaths, compared to very rapid de-containment processes.

In Spain, where decontamination was rapid for half the population and gradual for the rest, individual behavior will be key to reducing or avoiding a second wave. "If we manage to lower the transmission rate by 30% through the use of masks, hand hygiene and social distancing, we can reduce considerably the magnitude of the next wave. Reducing the transmission rate by 50% could prevent it completely," says Rodó.

The results show that even in countries that do not have the resources to test and track all cases and contacts, social empowerment through the use of masks, hand hygiene and social distancing is key to stopping viral transmission.

Simulations also show that the loss of immunity to the virus will have significant effects on the time between epidemic waves: if immunity is long lasting (one year instead of a few months), the time between epidemic waves will double.

The model takes into account total containment and uses data available up to 25 May, but does not take into account a possible effect of temperatures on viral transmission.