EClinicalMedicine 23 (2020) 100370 Contents lists available at ScienceDirect EClinicalMedicine journal homepage: https://www.journals.elsevier.com/eclinicalmedicine Commentary Serosurveys and convalescent plasma in COVID-19 rez-Cameoa, Juan Marín-Lahozb,* Cristina Pe a Emergency Department; Hospital Universitari Vall d’Hebron; Passeig de la Vall d’Hebron 119-129; 08035 Barcelona (SPAIN) b Neurology Department and Emergency Department; Hospital de la Santa Creu I Sant Pau; C/ Mas Casanovas 90; 08041 Barcelona (SPAIN) A R T I C L E I N F O overcome COVID-19. Furthermore, the real number of convalescent patients may be much greater than the number based on the recov- Article History: ery of previously identified patients because of the existence of Received 15 April 2020 asymptomatic and mild infections. This might be especially true in Revised 24 April 2020 Accepted 24 April 2020 countries where most of the incident infections had been acquired Available online 1 May 2020 from not previously identified cases. This is currently the case in sev- eral western countries. The estimates from the Imperial College Lon- The current pandemic is not only overwhelming the health systems don COVID-19 Response Team also support the hypothesis that most of the affected countries but also is killing thousands of other ways of the cases go unrecognized. According to their calculations, among healthy adults. Convalescent plasma has been proposed [1] and 11 European countries (comprising 375 million citizens) as of March approved to treat COVID-19 based on the experience acquired treating 30th there were about 18 million cases [4]. Populations that have other viral diseases such as influenza, Ebola, and SARS [2]. It is consid- been fully or randomly tested confirm the existence of asymptomatic ered a safe treatment (at least its side effects and contraindications are infections [5 7]. Accordingly, we propose two sources of donors, not well known) and it has proven to be efficacious in several viral infec- frequently identified, should be explored: paucisymtomatic patients: tions for more than a century. Currently, several countries and health and fully asymptomatic patients. institutions are trying to gather convalescent sera for either empirical Serosurveys might identify as many donors as required for the treatment or clinical trials. Based on the WHO interim guidance devel- growing number of patients who could benefit from convalescent oped for the 2014 Ebola outbreak [3], convalescent plasma has advan- plasma. Serosurveys have been used to evaluate the immunity of tages over other proposed treatment: it requires low technology (and some populations to infections such as Ebola and SARS after con- therefore it can be produced where required independent of pharma- trolling the outbreaks. They are very useful to evaluate the suscep- ceutical companies), it is low cost and its production is easily scalable as tibility of a population and therefore to calculate the peak of a long as there are sufficient donors. current or subsequent outbreak using the SIR model (susceptible, In other words, relative donor scarcity can threaten any plan to mas- infectious and recovered compartments) estimating the size of the sively produce treatments based on plasma. Due to the exponential recovered compartment. This in turn is used to decide health poli- nature of the pandemic, the number of current patients is greater than cies. To our knowledge, serosurveys have not been used to drive the number of recovered patients at any given time until the peak is plasma donations. In these diseases, known to have greater mor- reached. The number of identified recovered patients equals approxi- tality, a significant proportion of asymptomatics has been found mately the number of identified active patients three weeks earlier seropositive among exposed populations [8,9]. minus the deaths. In a supposed population with a steady growth of To boost the ability of serosurveys to find potential donors, the identified contagions of 20% something similar to what is currently going approach could be modified to enrich the sample (albeit not obtain- on in several cities around the world the number of active patients is ing representative data). Targeting populations at high risk of expo- between 17 and 87 times greater than the number of identified recov- sure such as contacts or health workers and self-identification of ered patients (potential donors). This means, in the best case scenario, potentially convalescent patients using questionnaires could easily there would be convalescent plasma available for 1 5% of the identified lead to as many plasma donors as required before the number of con- current patients. The actual number of donors will probably be much tagions peaks. lower as not every convalescent patient willing to donate would be suit- able (a great proportion are elder and have comorbidities) and not every Declaration of Competing Interest suitable potential donor will be willing to donate. Fortunately, infection by SARS-CoV2 is not as lethal as that caused We declare no competing interests. by Ebola virus and many patients do not require treatment to * Corresponding author. Funding rez-Cameo), E-mail addresses: crperez@vhebron.net (C. Pe juanmarinlahoz@gmail.com (J. Marín-Lahoz). No grants or financial support have been received for this work. https://doi.org/10.1016/j.eclinm.2020.100370 2589-5370/© 2020 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license. (http://creativecommons.org/licenses/by-nc-nd/4.0/) 2 C. Perez-Cameo and J. Marín-Lahoz / EClinicalMedicine 23 (2020) 100370 References [4] Flaxman S., Mishra S., Gandy A., et al.Estimating the number of infections and the impact of non- pharmaceutical interventions on COVID-19 in 11 European coun- tries. 2020; 35. [1] Chen L, Xiong J, Bao L, Shi Y. Convalescent plasma as a potential therapy for COVID- [5] Nishiura H, Kobayashi T, Suzuki A, et al. Estimation of the asymptomatic ratio of 19. Lancet Infect Dis 2020;20:398–400. novel coronavirus infections (COVID-19). Int J Infect Dis 2020 published online [2] Luke TC, Casadevall A, Watowich SJ, Hoffman SL, Beigel JH, Burgess TH. Hark back: March 13. doi: 10.1016/j.ijid.2020.03.020. Passive immunotherapy for influenza and other serious infections. Crit Care Med [6] Day M. Covid-19: identifying and isolating asymptomatic people helped eliminate 2010;38:e66–73. virus in Italian village. BMJ 2020;368. doi: 10.1136/bmj.m1165. [3] World Health Organization. Use of convalescent whole blood or plasma collected [7] Gudbjartsson DF, Helgason A, Jonsson H, et al. Spread of SARS-CoV-2 in the Icelan- from patients recovered from Ebola virus disease for transfusion, as an empirical dic population. Eng J Med 2020;0 null. treatment during outbreaks. Interim guidance for national health authorities and [8] Hoff NA, Mukadi P, Doshi RH, et al. Serologic markers for Ebolavirus among healthcare blood transfusion services. Geneva, Switzertland: WHO; 2014 https://apps.who. workers in the democratic republic of the congo. J Infect Dis 2019;219:517–25. int/iris/bitstream/handle/10665/135591/WHO_HIS_SDS_2014.8_eng.pdf;sequen- [9] Chen W-Q, Lu C-Y, Wong T-W, et al. Anti SARS-CoV Immunoglobulin G in Health- ce=1 (accessed April 3, 2020). care Workers, Guangzhou, China. Emerg Infect Dis 2005;11:89–94.