Antibodies for vaccinated with/without natural infection

[M_T]

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7532802/

Out of 155 American patients having undergone a PCR-based control subsequent to an initial positive finding, 88% remained positive 1 to 5 days later, and 56% out of the 105 patients tested afterwards remained positive at 21–25 days [6]. Median PCR negativation time in the 56 patients of the Chinese series by Xiao et al. was 24 days [7]. In Wuhan, 36/378 (9.5%) of patients having tested positive remained positive 30 days later, and in some cases their positivity lasted as long as 83 days [8]. The more severe the clinical presentation, the longer the duration of positivity, with a median of 31 days in a Chinese study involving 41 serious cases [9]. In a Singaporean study, 32% out of 766 COVID19 patients still remained positive at D21, 22% at D28 and 5% at D33

See also
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7417974/
https://www.news-medical.net/news/202106...tests.aspx

As a reminder, initially the CDC recommended a negative test to show one is over the disease. Then they switched to 10 days after symptom onset, presumably partly because of continued positive tests.

For COVID-19 isolation recommendations, see
https://www.cdc.gov/coronavirus/2019-nco...#isolation