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Rapid response to:


Covid-19: control measures must be equitable and inclusive

BMJ 2020; 368 doi: (Published 20 March 2020) Cite this as: BMJ 2020;368:m1141

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SARS-CoV-2 positive patients with few/no symptoms and modest levels of detectable viral RNA in the oropharynx have been described [1]. This claim, together with the observation that SARS-CoV-2 displays a well-known decay rate both in aerosols and various surfaces [2], suggests an intriguing possibility: when an otherwise healthy subject is exposed to a very low viral load, a partial immunization might occur that prevents severe COVID-19 forms. This mechanism, that we might term “mithridatization”, has been already described in animal models of the 2009 pandemic influenza virus, where decreasing the challenge dose resulted in reduction in clinical signs and delay in virus production in the upper respiratory tract [3]. This would mean that a low-dose challenge with SARS-CoV-2 might be administered to decrease the COVID-19 symptomatology, in particular in fragile patients.


1) Zou L, Ruan F, Huang M, Liang L, Huang H, et al. 2020. SARS-CoV-2 Viral Load in Upper Respiratory Specimens of Infected Patients. N Engl J Med 2020; 382:1177-1179. DOI: 10.1056/NEJMc2001737.
2) van Doremalen N, Bushmaker T, Morris DH, Holbrook MG, Gamble A, et al. 2020. Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1. N Engl J Med, DOI: 10.1056/NEJMc2004973.
3) Marriott AC, Dove BK, Whittaker CJ, Bruce C, Ryan KA, et al. 2014. Low dose influenza virus challenge in the ferret leads to increased virus shedding and greater sensitivity to oseltamivir. PLoS One, 9(4):e94090. doi: 10.1371/journal.pone.0094090.
4) Peiris JS, Chu CM, Cheng VC, Chan KS, Hung IF, et al. 2003. Clinical progression and viral load in a community outbreak of coronavirus-associated SARS pneumonia: a prospective study. Lancet. 2003 May 24;361(9371):1767-72.

Arturo Tozzi
Center for Nonlinear Science, Department of Physics, University of North Texas, Denton, Texas, USA

Gennaro D'Amato
Division of Respiratory and Allergic Diseases, Department of Chest Diseases, High Specialty A. Cardarelli Hospital, Napoli, Italy
Medical School of Specialization in Respiratory Diseases, University on Naples Federico II

Competing interests: No competing interests

21 March 2020
Arturo Tozzi
Gennaro D'Amato, Cardarelli Hospital, Napoli, Italy
ASL NA2 NORD, Caivano, Naples
via Amendola, 5, Caivano