One month ago, no matter where you lived, if you were a known close contact of an individual who became ill with COVID-19 or tested positive for the SARS-CoV-2 virus, your local public health officials would have asked you to self-quarantine for 14 days. But earlier this month, the Centers for Disease Control and Prevention (CDC) announced two new options to allow shorter quarantine periods for some individuals:
- A seven-day quarantine after testing negative on Day 5 or later, or
- A 10-day quarantine without testing.
State and local health departments may choose to stick with a 14-day quarantine requirement or adopt one or both shorter options. The Massachusetts Department of Public Health and the City of Cambridge are allowing both. However, for Covid Pass participants who access campus regularly, MIT will be accepting the second option only, requiring a quarantine period of at least 10 days.
Why quarantine?
Quarantine is intended to reduce the risk that infected individuals might unknowingly transmit infection to others. It also ensures rapid evaluation and treatment for individuals who develop symptoms or test positive during that time.
Health agencies like the CDC and World Health Organization (WHO) base their guidelines for quarantine periods on what is known of a virus’s possible incubation period — the time between exposure and the first symptoms of illness. Incubation periods vary from virus to virus, and different people develop symptoms at different rates within that incubation period.
In the case of COVID-19, the initial recommendation for a 14-day quarantine period was based on estimates of the upper bounds of the virus’s incubation period. Quarantine became an especially important aspect of the struggle to control the virus’s spread after research showed that people were able to transmit SARS-CoV-2 before developing symptoms and that a substantial portion of infected people remain asymptomatic but still able to transmit the virus.
Why the new quarantine options?
While the possible incubation period is still known to be as long as 14 days in some cases, we now have greater access to testing and know more about the typical progression of illness and infection after exposure. For example, a study of more than 7,000 confirmed cases in China during January and February showed the median incubation period to be 5 days. A later study obtained essentially the same result and also found that 97.5 percent of individuals who develop symptoms do so within 11.5 days of infection.
More recently, CDC scientists used a mathematical model to analyze the expected effectiveness of various combinations of symptom monitoring, testing, and quarantine to reduce the risk of transmission from infected individuals during and after travel. Using different estimates of the infectious period, test-positivity relative to infection, and test sensitivity, they found — not surprisingly — that a 14-day quarantine period was the most effective intervention, reducing risk of viral transmission by 97–100 percent in all conditions. But they also found that shorter quarantine periods could be combined with symptom monitoring and testing to achieve nearly as much risk reduction.
Based on observational and published data and its own modeling studies, the CDC estimates an approximately 5% risk of someone developing COVID-19 after their “seven days plus negative test” quarantine option and a 1% risk with the “10-day, no test option” that MIT is now using.
Both options require that individuals actively monitor themselves for symptoms and take their temperature at least once every day for a full 14 days from the date they were exposed to the virus — even after they are released from quarantine. Individuals who develop even mild symptoms or a temperature of 100°F or higher must self-isolate immediately and arrange to be tested.
If you are a Covid Pass participant
MIT’s contact-tracing team will supervise your 10-day quarantine. Unless you develop symptoms, you do not need to be tested during the quarantine period. However, if testing seems that it might be useful in your case, MIT’s contact tracers can work with you to help make those arrangements. On Day 11, once the contact-tracing team has spoken with you to confirm that you have remained asymptomatic, they will lift your Covid Pass hold.
You should get tested at one of MIT’s regular Covid Pass surveillance-testing sites the first available testing day that you are due to be on campus. As long as your previous test was done within the last 14 days, you will be able to access campus buildings and proceed with your normal campus activities the same day. However, if your previous test result is 14 days old or older, you will need to wait for a negative test result before your campus access is restored.
