Expected impact of COVID-19 outbreak in a major metropolitan area in Brazil

Tarcisio M Rocha Filho; Fabiana S. Ganem dos Santos; Victor B Gomes; Thiago A.H. Rocha; Julio H.R. Croda; Walter M Ramalho; Wildo N Araujo

In January 2020 China reported to the World Health Organization an outbreak of pneumonia of 2 undetermined origin in the city of Wuhan, Hubei. Initially 44 cases were reported, having as 3 common exposure contact the Wuhan seafood market. An increasing number of unrelated 4 secondary cases have since been detected across China, and leading to the dissemination of cases 5 into several countries [1] . The etiologic agent was identified as a new coronavirus, of the 6 betacoronavirus family, which has since be named SARS-CoV-2, and the resulting disease 7 COVID-19 [2] . In January 30, 2020, the World Health Organization declared the outbreak of 8 COVID-19 as a Public Health Emergency of International Interest (ESPII) [3, 4] , and in March 9 11 declared it a Pandemic [5] . 10 Previously to 2019, two highly pathogenic coronavirus had been described in the world. The 11 first named SARS-CoV and described in 2003, was responsible for an epidemic of severe acute 12 respiratory syndrome (SARS), initiated in China and with secondary cases in 26 other countries, 13 accounting for a total of 8,096 cases and 774 deaths [case-fatality rate (CFR): 9.6%] [6, 7] . The 14 second virus, named MERS-CoV, was identified in 2012 is a betacoronavirus responsible for the 15 Middle East Respiratory Syndrome (MERS) [8] . Cases of MERS-CoV are reported sporadically 16 ever since, resulting from zoonotic transmission, with a few outbreaks associated with human to 17 human transmission, resulting in 2449 cases and 845 deaths (CFR: 34,5%), with the majority 18 (84%) reported in Saudi Arabia [9] . 19 SARS-CoV-2 has significant differences relative to MERS-CoV and SARS-CoV. In just over 20 a month of the epidemic, more cases of COVID-19 were confirmed than in the entire history of 21 22 linked to epidemic amplification phenomena, with few cases were responsible for a 23 disproportionately high number of secondary cases, the so-called super-spreaders, with a 24 significant number of cases resulting from nosocomial transmission. This characteristic allowed 25 outbreaks to occur even in scenarios with an average basic reproduction number R 0 of less than 26 one [4, [10] [11] [12] [13] [14] . Unlike SARS-CoV and MERS-CoV, over-dispersion events does not seem to be 27 of a major relevance for the COVID-19 epidemic, suggesting a more homogeneous 28 transmissibility in the population [15, 16] . 29 Homogeneous transmissibility and the potential for transmission from asymptomatic 30 sources [17] brings COVID-19's behavior closer to other respiratory transmission viruses, such 31 as measles or influenza [13] . Influenza viruses, despite the differences in relation to viruses of 32 the coronavirus family, have similar modes of transmission, and the associated clinical 33 syndromes. Eventually new influenza viruses originating from genetic recombination in animals 34 infect humans, and subsequently transmitted in the population, having been responsible for 35 pandemics in the past, with the occurrence of hundreds of thousands of cases and thousands of 36 deaths worldwide [18, 19] .