The CDC recommends this 90 day window because a "positive" test result is more likely to be due to your previous illness than a new infection. Therefore, testin

The CDC recommends this 90 day window because a "positive" test result is more likely to be due to your previous illness than a new infection. Therefore, testing is useless because it gives you no useful information [1] > for adults recovered from SARS-CoV-2 infection, a positive SARS-CoV-2 RT-PCR result without new symptoms during the 90 days after illness onset more likely represents persistent shedding of viral RNA than reinfection It does NOT mean that you are suddenly susceptible after 90 days - just that after 90 days, you are less likely to be actively shedding the previous infection so the tests are useful again [1] https://www.cdc.gov/coronavirus/2019-ncov/hcp/duration-isolation.html https://www.cdc.gov/coronavirus/2019-ncov/hcp/duration-isola...