Retrospective analysis of the Italian exit strategy from COVID-19 lockdown

Valentina Marziano; Giorgio Guzzetta; Bruna Maria Rondinone; Fabio Boccuni; Flavia Riccardo; Antonino Bella; Piero Poletti; Filippo Trentini; Patrizio Pezzotti; Silvio Brusaferro; Giovanni Rezza; Sergio Iavicoli; Marco Ajelli; Stefano Merler

doi:10.1073/pnas.2019617118

New Research In

Edited by Andrea Rinaldo, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland, and approved December 14, 2020 (received for review September 18, 2020)

Significance

We use a mathematical model to evaluate the Italian exit strategy after the lockdown imposed against the COVID-19 epidemics, comparing it to a number of alternative scenarios. We highlight that a successful reopening requires two critical conditions: a low value of the reproduction number and a low incidence of infection. The first is needed to allow some margin for expansion after the lifting of restrictions; the second is needed because the level of incidence will be maintained approximately constant after the reproduction number has grown to values close to one. Furthermore, we suggest that, even with significant reductions of transmission rates, resuming social contacts at prepandemic levels escalates quickly the COVID-19 burden.

Abstract

After the national lockdown imposed on March 11, 2020, the Italian government has gradually resumed the suspended economic and social activities since May 4, while maintaining the closure of schools until September 14. We use a model of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission to estimate the health impact of different exit strategies. The strategy adopted in Italy kept the reproduction number R_t at values close to one until the end of September, with marginal regional differences. Based on the estimated postlockdown transmissibility, reopening of workplaces in selected industrial activities might have had a minor impact on the transmissibility. Reopening educational levels in May up to secondary schools might have influenced SARS-CoV-2 transmissibility only marginally; however, including high schools might have resulted in a marked increase of the disease burden. Earlier reopening would have resulted in disproportionately higher hospitalization incidence. Given community contacts in September, we project a large second wave associated with school reopening in the fall.

Footnotes

↵¹V.M. and G.G. contributed equally to this work.
↵²To whom correspondence may be addressed. Email: merler{at}fbk.eu.

Author contributions: G.G., S.B., G.R., S.I., M.A., and S.M. designed research; V.M., G.G., B.M.R., F.B., P. Poletti, and F.T. performed research; V.M., G.G., B.M.R., F.B., A.B., P. Poletti, and F.T. analyzed data; and V.M., G.G., F.R., P. Poletti, F.T., P. Pezzotti, M.A., and S.M. wrote the paper.
Competing interest statement: M.A. has received research funding from Seqirus. The funding is not related to COVID-19. All other authors declare no competing interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.2019617118/-/DCSupplemental.