Press Release N° 2/2021-The FBK-ISS-INAIL study. Reopening is risky, even with an RT below 1

Rome, 08 January 2021

Easing restrictions when the incidence of Sars-CoV-2 infections is still high may rapidly lead to a new spike in cases, and therefore in hospital admissions, even if the RT is below 1. This has been demonstrated by a study, based on data from the 'first wave' of the epidemic, carried out by researchers of the Bruno Kessler Foundation (FBK), the Italian National Institute of Health (ISS) and the National Institute for Occupational Accident Insurance (INAIL). The study has been published in the journal Proceedings of the National Academy of Science of the United States (PNAS). https://www.pnas.org/content/118/4/e2019617118

A virus transmission model was used in the study to estimate the impact of various mitigation strategies, together with a new method for assessing risk in different production sectors. The results of this research were used to define the possible scenarios associated with phase 2, that is to say the reopening after the lockdown, and to define the possible scenarios and interventions that could be adopted in the autumn.

As for the timing of the lifting of restrictions on social contacts, the research shows that premature reopening may significantly speed up the progress of the epidemic. For example, had the lockdown ended on 20 April instead of 18 May there would have been an approximately 500% increase in cumulative admissions to hospital compared to the cases observed from May to the end of September.

The analysis shows that an RT below 1 is necessary to have some margin after the lifting of restrictions, while the low incidence is necessary to maintain the number of new cases (and therefore admissions to hospital and deaths) at an approximately constant level after the RT returns to values close to 1 following the easing of restrictions. This, for example, happened last summer: the national RT was estimated at around 3 in February, and it then dropped substantially below 1 in a matter of two weeks following the lockdown imposed on 11 March, and then rose again to values close to and even slightly higher than 1 following reopening on 18 May. "In particular - explains Stefano Merler, FBK researcher, the incidence must be low enough for the prevention systems to manage the situation i.e. isolating the new cases and putting contacts in quarantine. Based on the period when the prevention services started coming under pressure because of the increase in the incidence of new cases during the second wave, it was found that the incidence needs to  be less than about 50 cases per week per 100,000 inhabitants to keep things under control".
"The research - continues Merler - shows that the transmission potential of COVID-19 is still very high and suggests extreme caution in resuming social contacts and in the timing with which the contacts are reactivated".

Which restrictions should be lifted first?
As regards the easing of restrictions on social contacts, the research shows that:
 
•    contacts in occupational environments, excluding essential services (e.g. health care) which may be at high risk but cannot be closed down, may not have a heavy impact on the transmissibility of SARS-COV-2;
•    it is however important to encourage smart working as much as possible and where possible;
•    the reopening of schools, from kindergartens to middle schools, may have a limited impact on the transmissibility of SARS-COV-2 due to the lower susceptibility to infection of children and of youngsters below the age of about 14; 
•    an almost full reactivation of social contacts and the reopening of schools of all levels, as occurred in late summer, may result in an epidemic wave that might not be contained without the adoption of very severe restrictive measures.

The analysis carried out does not allow to distinguish between infection transmitted within the school buildings and infection transmitted during school activities outside of the actual buildings (for example, transport, possible gatherings outside school buildings, extra-curricular activities).

Before October, 5% of the Italian population was infected
The authors estimated that up to 30 September about 4.8% of the Italian population was infected, with major differences between Regions (about 11% in Lombardy, 2% in Lazio and 1% in Campania). As a consequence, the analysis suggests that the effects of reopening may differ from Region to Region as a result of the different levels of immunity achieved and the different prevalence of the infection. The research also suggests that demographic structure may play a role, with a lower impact of COVID-19 in Regions with younger populations.

Increased diagnostic capacity
Finally, the authors estimated that the notification rate (how many infections are detected by the surveillance system with respect to the total number of infections, therefore including all asymptomatic cases) increased from about 9.4% during the first wave to about 24.5% during the summer, probably due to improved contact tracing capabilities in situations where the daily incidence is low.