COVID-19 household study to assess secondary attack rates and the proportion asymptomatic, including children

The spectrum of illness associated with "Coronavirus Infectious Disease 2019" (COVID-19) due to the SARS-CoV-2 virus varies a lot. Most people experience mild or moderate illness but some experience severe illness requiring hospitalization or resulting in death. Cases without any symptoms (called asymptomatic) have also been reported but how frequently that occurs is hard to know because people with asymptomatic infections are less likely to be seen by a health care professional or to be tested for the virus. Children appear to be less affected overall by the pandemic, but some reports suggest they are more likely to have mild or asymptomatic infections so may also be missed. To get a better understanding of the extent to which mild or asymptomatic infections, including children, contribute to the overall burden and spread of COVID-2019, we propose a household study involving families with children in British Columbia (BC) and Quebec. When the first case in a household is identified, we will actively follow all of the household members for infection over a one-month period. We will measure how many become infected by testing them for SARS-CoV-2 antibodies in their blood at the start and end of the one-month period and by asking them to self-collect respiratory specimens weekly. All household members will complete a daily diary of symptoms so we can compare their test results to their symptom severity, including whether they had been infected without even knowing it (asymptomatic). To study immune responses and viral shedding in more detail, we will also offer a subset of households to participate in more intensive sampling. These findings will clarify the role of asymptomatic infections and children and help public health authorities navigate the next stages of the pandemic.