If someone in my house has COVID-19, how likely am I to get it?
What is the risk of COVID-19 transmission within my household, if everyone is unvaccinated?
Secondary Attack Rate (SAR) is a measure of disease transmissibility. It is the proportion of people within a group who get sick after exposure to an infected person. This doesn’t count people who are currently infected or who are fully vaccinated. For example, if 2 people get COVID-19 after a birthday party with 5 unvaccinated people, the SAR would be 2 out of 5 or 40%.
The SAR is higher within households, largely because family members and housemates spend longer periods of time together, are in closer proximity, and share high-touch surfaces. Overall estimates of SARS-CoV-2 have found an overall SAR of about 18%, or 1 in 5, for household contacts.
What is the risk of COVID-19 transmission within my household when I am fully vaccinated?
If you are exposed to someone in your house who has COVID-19, the risk of becoming infected is low if you are fully vaccinated. However, certain conditions could increase your risk, including: if the infected person is symptomatic, you’re in a COVID-19 hot spot, or you live in a group setting (e.g., correctional facilities, dormitory, nursing home).
The SAR in a household of people of mixed vaccination status is not zero. Therefore, household members that are sick should isolate themselves, and other members should follow quarantine guidelines for vaccinated and unvaccinated people.
How will COVID-19 variants affect household transmissibility?
There are currently five COVID-19 variants of concern, commonly referred to as the country in which they were first detected: United Kingdom (B.1.1.7), South Africa (B.1.351), U.S. California (B.1.427, B.1.429), and Brazil (P.1). All five are in the United States and are more contagious. Evidence on how the variants impact household SAR is limited. But initial studies suggest that the household SAR is 60% higher for the UK variant.
Last update: Apr 8, 2021, 16:40pm ET
Science review: HAY, JAB