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Good news! Your son can come out of isolation and rejoin society, albeit in a manner respecting continued universal masking, physical distancing, hand hygiene, and the other measures needed to avoid COVID-19. According to CDC’s Guidance your son’s first opportunity to come out of isolation would have been:
At least 10 days since symptoms first appeared AND
At least 24 hours with no fever (without using a fever-reducing medication) AND
Other symptoms are resolving
So, according to your son’s scenario, he never had a fever and had rapid resolution of symptoms (no, he does not have to wait until the throat tingling is gone) and so could have come out from isolation at day 10 (after 10 days) from the onset of symptoms. A repeat COVID-19 test would only be necessary if there were new symptoms of a possible COVID-19 infection.
The CDC’s Guidance is here. https://www.cdc.gov/coronavirus/2019-ncov/if-you-are-sick/isolation.html