To study the level of neutralizing antibodies produced in the population at different time intervals after completion of the inactivated 2019-nCoV vaccine immunization, and to evaluate the protective effect produced by the vaccine in the population.

Fifty volunteers were included in this study, the neutralizing antibodies were detected by ELISA, and the inhibition rate and positive rate were calculated from the absorbance OD value.

The positive rates were 76% (38/50), 68% (34/50), 30% (15/50) and 100% (50/50) in the groups of 6, 8, 10 months’ intervals and intensive immunization, respectively; while the mean suppression rates were 58.80%, 49.86%, 34.60 and 95.55%, respectively. The result of the time main effects test showed that there was a statistically significant difference in the mean inhibition rate between the different time periods (F = 326.00, P<0.001). The paired t-test showed a gradual decrease in the mean inhibition rate in the 6th, 8th and 10th month, with a significant increase (P<0.001) after 7-day in intensive immunization.

This study showed after two doses of the 2019-nCoV vaccine, the level of neutralizing antibodies gradually decreased and weakened over time, but there was immune memory in the body, and when the body intensively stimulated by vaccine again, the level of neutralizing antibodies would rise significantly.

Inactivated 2019-nCoV vaccine; Neutralizing antibodies; Inhibition rate; Positive rate