The Missouri Department of Health and Senior Services and the Department of Elementary and Secondary Education have modified shared guidance for determining close contacts and assessing exposures in school settings. Under the updated guidance, proper mask wearing may now prevent individuals from being identified as close contacts in K-12 schools that have implemented a mask mandate. This means that if both individuals at school – the person diagnosed with COVID-19 and the person exposed to the positive case – have masks on and are wearing them correctly, the individual exposed does not need to quarantine.
See the updated guidance here: https://dese.mo.gov/.../COVID-MO-K12-Reopening-Guidance.pdf
