This could be because:
– Antibody status (both the level of the antibodies and the type of antibodies) changes over time from the point of infection, and so antibody levels may have declined over time.
– You may have been exposed to COVID-19 but have different antibodies that this research test is not designed to pick up.
You should continue to follow all guidance on self-isolation and social distancing as appropriate. In addition, we encourage all study members to have the COVID-19 vaccine when offered, regardless of antibody results.