Our aim is to study the household transmission dynamics of SARS-CoV-2 in a slum in Rio de Janeiro, Brazil and to estimate the immunity of the study population against the new virus. We will examine and test a sample of children and their families for SARS-CoV-2. Recruitment will take place at a primary health clinic, located in one of the poorest neighbourhoods of the city. We will recruit children 0 to 13 years of age who are brought to the clinic to receive free vaccinations. With the written informed consent from the child's guardian, we will collect the study samples. Afterwards we will visit the child's home to collect samples of all residents, with four follow-up visits in the first month, every three months during the first year and twice in the second year. We hope to uncover the role of children in the disease transmission.

The overall aim of this study is to gain an understanding of the transmission dynamics of COVID19 to household contacts of children, as well as rapid and early information on key clinical, epidemiological, virological characteristics of SARS-CoV-2 infection, and_x000D_ immunity. This household transmission study will provide key epidemiological data on: the proportion of asymptomatic cases and symptomatic cases; the incubation period of SARS-COV-2 and the duration of infectiousness and of detectable shedding; the serial interval of SARS-COV-2 infection; the reproduction numbers: R0 and R of SARS-COV-2; clinical risk factors for COVID-19, and the clinical course and severity of disease; high-risk population subgroups; the secondary infection rate and secondary clinical attack rate of SARS-COV-2 infection among household contacts; and patterns of health-care seeking._x000D_ The secondary objective is to estimate the immunity of the study population over a period of 18 months by assessing the seroprevalence of antibodies to SARS-CoV-2 (IgG) and the kinetics of neutralizing antibodies of children and household contacts.