Modelling the SARS-CoV-2 first epidemic wave in Greece: social contact patterns for impact assessment and an exit strategy from social distancing measures

Abstract

In Greece, a nationwide lockdown to mitigate the transmission of SARS-CoV-2 was imposed on March 23, 2020. As by the end of April the first epidemic wave is waning, it is important to assess the infection attack rate and quantify the impact of physical distancing. We implemented a survey to assess social mixing patterns before the epidemic and during lockdown. We estimated R0 from surveillance data and assessed its decline as a result of physical distancing based on social contacts data. We applied a Susceptible-Exposed-Infectious-Recovered model to estimate the infection attack rate and the infection fatality ratio (IFR). As multiple social distancing measures were implemented simultaneously (schools/work/leisure), we assessed their overall impact as well as their relative contribution. R0 was estimated 2.38 (95%CI: 2.01,2.80). By April 26th, the infection attack rate was 0.12% (95% CrI: 0.06%,0.26%) and the IFR 1.12% (95% CrI: 0.55%,2.31%). During lockdown, daily contacts were reduced by 86.9% and the effective reproduction number reached 0.46 (95% CrI: 0.35,0.57). The reduction in R0 attributed to lockdown was 81.0% (95% CrI: 71.8%,86.0%) whereas the reduction attributed to each measure separately ranged between 10%-24%. We assessed scenarios with less disruptive social distancing measures as well as scenarios where measures are partially lifted after lockdown. This is the first impact assessment of the first wave of SARS-CoV-2 in a European country. It suggests that only multiple measures implemented simultaneously could reduce R0 below 1. Measuring social mixing patterns can be a tool for real-time monitoring of the epidemic potential.

Factors determining different death rates because of the COVID-19 outbreak among countries

“…However, it does imply that this is a possibility and focused research is needed to clarify it. It is in relative contrast with a report suggesting that the lockdown was the strongest measure with 81% or R 0 reduction attributed to it, but the methodology of that study was quite different from ours and based on self-report data ( 6 ). That study also suggested that that only multiple measures implemented simultaneously could reduce R 0 below 1.…”

Antibodies against SARS-CoV-2 among health care workers in a country with low burden of COVID-19

“…As of May 30, there were 2,915 confirmed cases and 175 related deaths in Greece with a death rate of 16 per 1,000,000 population, which is one of the lowest in Europe [ 2 ]. Modelling data suggest that by the end of April 2020, when the first wave of epidemic was completed, the infection attack rate in Greece was 0.12% (95% Crl: 0.06–0.26) which corresponds to 13,200 total infections (95% Crl: 6,206–27,700) and a case ascertainment rate of 19.1% (95% CI 9.1–40.6) [ 3 ].…”

A Novel Approach for Estimating the Final Outcome of Global Diseases Like COVID-19

“…Even for a country like Greece, which was one of the countries that took measures very early and succeeded to combat the disease, a relevant study after using a SEIR model was predicting a cumulative number of confirmed cases approximately at 12K with a confidence interval [4.5K,27.5K], see Fig. 3 of [21]. Currently Greece has a cumulative number of 3.4K confirmed cases, smaller even from the lower edge of predicted interval.…”

“…The model predictions of [21] are presented at their Fig. 1 where the model has been fitted to the available data til April 26.…”

“…Now it is the winter at South and a new cycle has began. We can estimate the approximate begin date if we apply method EDE for the curve of Figure 13: The 4 EDE-stages for COVID-19 in Greece for the study time of [21] global cumulative deaths, after its inflection point. Then we find a new turning point on May-27, see Fig.…”