ACE2 and COVID-19: However, as the rationale for booster COVID-19 vaccine doses following primary vaccine schedules is based on post-dose increases in NAb levels from baseline (56) and as there was no significant difference in ACE2-RBD binding inhibition demonstrated by LFA result categories, conclusions cannot be drawn from these results in relation to booster COVID-19 vaccine doses in those with “Weak Positive” or “Positive” results via LFA.