How rare is it for that to happen? @ExGingi seemed to be implying it *never* happens.
Local public health authorities determine and establish the quarantine options for their jurisdictions. CDC currently recommends a quarantine period of 14 days. However, based on local circumstances and resources, the following options to shorten quarantine are acceptable alternatives.
Quarantine can end after Day 10 without testing and if no symptoms have been reported during daily monitoring.
With this strategy, residual post-quarantine transmission risk is estimated to be about 1% with an upper limit of about 10%.
When diagnostic testing resources are sufficient and available (see bullet 3, below), then quarantine can end after Day 7 if a diagnostic specimen tests negative and if no symptoms were reported during daily monitoring. The specimen may be collected and tested within 48 hours before the time of planned quarantine discontinuation (e.g., in anticipation of testing delays), but quarantine cannot be discontinued earlier than after Day 7.
With this strategy, the residual post-quarantine transmission risk is estimated to be about 5% with an upper limit of about 12%.
In both cases, additional criteria (e.g., continued symptom monitoring and masking through Day 14) must be met and are outlined in the full text.
CDCAdditional sources on ending quarantine early with a negative PCR test:
https://www.medrxiv.org/content/10.1101/2020.10.27.20211631v4https://www.medrxiv.org/content/10.1101/2020.08.21.20177808v3https://www.medrxiv.org/content/10.1101/2020.11.23.20237412v1In short: it appears that quarantining contacts for 14 days from exposure reduces transmission risk by nearly 100%. Reducing quarantine to 10 days (with no symptoms) appears to still lower transmission risk by ~98%, while further reducing quarantine to 7 days with a negative PCR test seemingly still decreases transmission risk by ~95%. Exercising extreme caution for the remaining 4-7 days (mask wearing, avoiding crowds, distancing, and symptom monitoring) further reduces ongoing transmission risk.
It’s certainly likely that with a quarantine period cut in half, compliance would rise dramatically. Additionally, it’s reasonable to assume it would be better for the economy, mental health, education, etc. If the virus is not heavily prevalent in a population it may be worthwhile to eliminate as many avenues of transmission as possible despite the cost but where we currently stand as a country the CBA certainly seems to greatly favor increasing compliance at the cost of somewhat elevated transmission risk. The fact that this would encourage greater testing among exposed contacts would definitely be helpful as well.
IMO, in a population with a large amount of immunity (like Lakewood or BP), even where the virus is not heavily prevalent, it makes sense to adopt a policy of 7 days plus a negative PCR. However, that is only true if all or most contacts will comply with quarantine policies (unlike Lakewood or BP). Otherwise, even the slightly elevated risk can get blown out of proportion by a few irresponsible people due to the k factor.