Because there is no scientific basis for a 14 day quarantine. The CDC reduced the number and their reduced number is actually very conservative. There are studies that came out shortly before they made the change. The policies we implemented were all based on SARS, and it was very different. France has now dropped its period to 7 days, Germany 5 days. Based on the research 7 is probably the safe number.
“Even if you were to get the P.C.R. test right on the very first day that you could, by the time you get the results back, 90 percent of your shedding has been completed,” said Dr. Michael Mina, a virologist at the Harvard T.H. Chan School of Public Health. “This meta-analysis shows just how short your transmission window is.”
Should Isolation Periods Be Shorter for People With Covid-19? - The New York Times (nytimes.com)
Gotta keep in mind the difference between isolation and quarantine. For people that have tested positive, the new CDC isolation is 10 days. The German and France periods are also for isolation. It's for infected people, Isolation is infected. But you do need to back date it to the day your symptoms onset, not from when you got your test results. As the article mentions, live shedding ends about 9 days after symptom onset.
But this is not the same as the quarantine period. For those who have had a close contact, you first need to wait for symptoms before starting that 10 day clock. 100% of people who had symptoms report them by day 14. That's where the scientific basis for 14 days came into play. This was a Wuhan COVID study (confirmed multiple times later), not on OG SARS. It's the quarantine period after a contact waiting to see if you get symptoms, not isolation period. Unfortunately a basketball team is one just one giant close contact.
Where the confusion comes in is that most people report symptoms around day 5 (median is day 4-5) and with those 10 days of isolation you coincidentally also end up at 14 days from contact. So you're advised to wait 14 days after contact to see if you get symptoms, and also most people in general are done shedding by 14 days after contact. Which is why it's a good number of days to use as a general public health advisory.
But yes, that 14 day quarantine window is conservative. 98% of people have developed symptoms by day 12. 90% by day 10. 75% by day 7, 50% by day 5. There is a public health number between days 5 and 12 from contact that would be more palatable while also preventing the majority of pre-symptomatic spread (which can be full blast 2 days before symptom onset). 14 days for quarantine is too conservative.
Correspondingly, false negative PCR tests are high until between days 5 and 8 for those who develop symptoms on day 5. But for those 50% who develop symptoms after day 5, the false negative rates are still extremely high until 1-3 days after symptom onset. So yes, it would be great to test people out of quarantine, but where do you set the threshold considering the accuracy of the tests? This is what just happened to UConn as the student athlete tested negative twice while it turns out they were infected until testing positive on what was likely the 3rd test later on day 6 or 7.
If 75% of people develop symptoms by day 7, that means by day 8 or 9 you should have a strong likelihood that a negative test will clear someone (or they've already developed symptoms). I would throw in a test before then as well for further confirmation. So my personal policy would be 2 negative tests for asymptomatic people both taken after day 7 from contact or totally asymptomatic through day 10 with no tests. And then the CDC recommended 10 days isolation from symptom onset for those with a positive case.
