inclusion criteria: 1. aged 18 to 80 years. 2. history of close contact or exposure to positive covid-19 cases in the same household. 3. absence of symptoms resembling covid-19 (e.g., fever and acute respiratory or gastrointestinal symptoms) for two weeks prior to enrolment for the study. 4. able to give informed consent or in case of \<21 and\>/=18 years old subject, parents able to give consent for those individuals. in the event the household is unable to read or sign/date the icf, an impartial witness to be present to ascertain the information, comprehension and voluntariness. the impartial witness must be able to read the informed consent form (icf). 5. able to comply with study procedures and follow-up 6. singapore citizen, permanent resident or long-term pass-holder.

inclusion criteria: 1. aged 18 to 80 years. 2. history of close contact or exposure to positive covid-19 cases in the same household. 3. absence of symptoms resembling covid-19 (e.g., fever and acute respiratory or gastrointestinal symptoms) for two weeks prior to enrolment for the study. 4. able to give informed consent or in case of \<21 and\>/=18 years old subject, parents able to give consent for those individuals. in the event the household is unable to read or sign/date the icf, an impartial witness to be present to ascertain the information, comprehension and voluntariness. the impartial witness must be able to read the informed consent form (icf). 5. able to comply with study procedures and follow-up 6. singapore citizen, permanent resident or long-term pass-holder.

inclusion criteria: aged 18 to 80 years. history of close contact or exposure to positive covid-19 cases in the same household. absence of symptoms resembling covid-19 (e.g., fever and acute respiratory or gastrointestinal symptoms) for two weeks prior to enrolment for the study. able to give informed consent or in case of <21 and>/=18 years old subject, parents able to give consent for those individuals. in the event the household is unable to read or sign/date the icf, an impartial witness to be present to ascertain the information, comprehension and voluntariness. the impartial witness must be able to read the informed consent form (icf). able to comply with study procedures and follow-up singapore citizen, permanent resident or long-term pass-holder.

inclusion criteria: aged 18 to 80 years. history of close contact or exposure to positive covid-19 cases in the same household. absence of symptoms resembling covid-19 (e.g., fever and acute respiratory or gastrointestinal symptoms) for two weeks prior to enrolment for the study. able to give informed consent or in case of <21 and>/=18 years old subject, parents able to give consent for those individuals. in the event the household is unable to read or sign/date the icf, an impartial witness to be present to ascertain the information, comprehension and voluntariness. the impartial witness must be able to read the informed consent form (icf). able to comply with study procedures and follow-up singapore citizen, permanent resident or long-term pass-holder.

inclusion criteria: 1. aged 18 to 80 years. 2. history of close contact or exposure to positive covid-19 cases in the same household. 3. absence of symptoms resembling covid-19 (e.g., fever and acute respiratory or gastrointestinal symptoms) for two weeks prior to enrolment for the study. 4. able to give informed consent or in case of <21 and>/=18 years old subject, parents able to give consent for those individuals. in the event the household is unable to read or sign/date the icf, an impartial witness to be present to ascertain the information, comprehension and voluntariness. the impartial witness must be able to read the informed consent form (icf). 5. able to comply with study procedures and follow-up 6. singapore citizen, permanent resident or long-term pass-holder.

inclusion criteria: 1. aged 18 to 80 years. 2. history of close contact or exposure to positive covid-19 cases in the same household. 3. absence of symptoms resembling covid-19 (e.g., fever and acute respiratory or gastrointestinal symptoms) for two weeks prior to enrolment for the study. 4. able to give informed consent or in case of <21 and>/=18 years old subject, parents able to give consent for those individuals. in the event the household is unable to read or sign/date the icf, an impartial witness to be present to ascertain the information, comprehension and voluntariness. the impartial witness must be able to read the informed consent form (icf). 5. able to comply with study procedures and follow-up 6. singapore citizen, permanent resident or long-term pass-holder.