Virus re-emergence after lockdown ends

A new report in the journal Nature Human Behaviour in June 2020 reports predictions as to the effects of removing lockdown restrictions on the transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and suggests that individual responsibility concerning social distancing and other precautions could avoid the need for lockdowns.

The ongoing COVID-19 pandemic is in different phases in different countries, waning in some former hotspots but rising rapidly in others. Since there are no antivirals to prevent or treat infections, the only preventative measure available is social distancing and lockdowns.

Study: The end of social confinement and COVID-19 re-emergence risk Image Credit: ImageFlow / Shutterstock
Study: The end of social confinement and COVID-19 re-emergence risk Image Credit: ImageFlow / Shutterstock

Lockdowns: How Long, How Much?

As of now, lockdowns are being gradually relaxed in several places, but with significantly different policies in place. The lack of information about the factors that could affect the occurrence of a second wave of infection, like that which occurred after the 1918 influenza pandemic, makes it challenging to identify the best interventions to relax strict lockdowns while maintaining safe precautions against the viral spread.

The World Health Organization issued interim guidelines on the best way to lift confinement measures, given the current virus activity level. The effectiveness of the strict lockdown at the peak of the Italian and Spanish epidemics also poses a challenge: will the number of fatalities increase as mobility increases?

The researchers note: “The first evaluation studies seem to indicate that the national emergency response appeared to have delayed the growth and limited the size of the COVID-19 epidemic in China, averting hundreds of thousands of cases.”

The Study: Identifying Effects of Lockdown Relaxation

The current study by researchers Leonardo López & Xavier Rodó at the Barcelona Institute for Global Health aimed at projecting the degree of restriction on population-wide movements, and the effect of different plans to ease the lockdown to assess the risk. Despite the lack of understanding about the principles of virus transmission and the best way to prevent such spread, some measures such as the use of face masks, gloves, hand sanitation and remaining at home unless for essential work and necessities of life, have shown their utility in restricting the speed of spread. These were also meant to be independently evaluated in terms of the quantitative benefit they confer.

An earlier study by the same researchers tested control intervention models in Spain and Italy. The current research incorporates another parameter to simulate the return of people from confined to the susceptible population compartment to understand the effect of allowing different compartments to mix partially.

The difference in the new parameter is that all those coming from the confined and exposed compartment, who are in quarantine, are not included. This is to avoid the instability introduced by the large but unknown number of asymptomatic people.

Instead, confined now means those who are in the susceptible compartment and protected from infection. This assumption deliberately overlooks the unknown but significant number of household contacts. Hospital-acquired contacts are also excluded, as in any current model of an ongoing epidemic, due to highly unreliable and limited data. In short, these assumptions mean that the result will be an underestimation of the actual burden of disease.

Different Relaxation Models

The model envisages a release of people at 50% higher than the confined population. Two strategies are explored, both dealing with gradual relaxation. The first is a steady release, whereas the second is a two-phase release with more high-risk people being released much later.

In another model, they simulated the results of abruptly releasing 50% of people at 45, 60 and 75 days from March 13, followed by a gradual release at the same time points from the first deconfinement.

They also simulated a benchmark simulation with all the people being released suddenly, at the same time points: 30 days, 60 days, and 90 days from the lockdown. Finally, a reference model is created using the most current observations (the Current model).

The study was further extended to see how these protocols would affect other countries like Japan, and New Zealand, which dealt with the lockdown differently but have had great success. Finally, the US scenario was also explored, being the worst affected country, along with Indonesia as a tropical model, and Argentina as a country rapidly approaching winter.

Second Peak Inevitable, Severity and Timing Modifiable

The results show that a second peak will occur in all scenarios, but the peak will be delayed with an increasing duration of lockdown. For the ‘current’ scenario, the second peak will be earlier, in the middle of August. This modeling assumes all released people do not use any precautionary measures and are entirely susceptible. Seasonal effects are also ignored.

The three lockdown durations in the first protocol differ, as stated earlier, in the time of the second peak. With a 30-day lockdown, the second peak arrives in mid-September, with about 10 million cases. With the 60-day lockdown, the peak is in December, and with the 90-day lockdown, well after the New Year in 2021.

The Current scenario is associated with a more significant number of deaths by almost a third. With the mixed scenario, half being released at once and half later on, the 45-day time point results in a rapid high early second peak around mid-August, at about 6 million cases.

Shorter lockdown durations, however, cause later secondary peaks but at the cost of double the number of infections, to over 50%. The number of deaths is also projected to double by the end of 2020 with the 60-day lockdown, compared to the 45- and 75-day lockdowns.

While the simulations fit the Japanese and New Zealand observations well, with the USA, the second peak is shown with about 40-50 million cases at about the start of 2021 given a lockdown duration of 90 days. Argentina shows a delayed peak, December to February, with a 100-days lockdown, as does Indonesia, which shows a delayed peak of about 40 million after 45 days, and 32 million after 100 days.

Implications and Recommendations

The researchers comment, “Gradual deconfinement strategies always result in a lower number of infections and deaths, when compared to the sudden release of moderate to large portions of the population.”

If this is not feasible, they recommend a mixed or two-phase relaxation, where the most high-risk groups are shielded completely, but others can exit as long as they continue with social distancing and other relevant measures, along with testing and tracing.

They also warn, “Our results are in line with others showing that, in the absence of other control measures (for example, increases in case detection, isolation, and/or contact tracing), widespread relaxation of social distancing will result in a resurgence of cases, which will most likely overwhelm healthcare capacity.” The lowest mortality is seen, as well as the highest total number of cases, with the longest lockdown duration of 90 days.

The researchers also note that reduction of spread by even a third, as well as a longer duration of immunity, reduces the size of the second peak

Journal reference:
Dr. Liji Thomas

Written by

Dr. Liji Thomas

Dr. Liji Thomas is an OB-GYN, who graduated from the Government Medical College, University of Calicut, Kerala, in 2001. Liji practiced as a full-time consultant in obstetrics/gynecology in a private hospital for a few years following her graduation. She has counseled hundreds of patients facing issues from pregnancy-related problems and infertility, and has been in charge of over 2,000 deliveries, striving always to achieve a normal delivery rather than operative.

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