Objective To investigate the levels of neutralizing antibodies against the novel coronavirus in the serum of elderly individuals aged 60 years and above in Shanghai’s Changning District， following natural infection and mixed immunity， in order to provide a basis for strengthening immunity in the elderly.

Methods Elderly people who participated in free health check-ups at 10 community health service centers in Changning District from May to June 2023 were selected as the subjects. Information such as gender， age， COVID-19 infection history， COVID-19 vaccine immunization history， and chronic disease history were collected. Serum samples of the subjects were collected and quantitative detection of SARS-CoV-2 neutralizing antibodies was performed by magnetic particle chemiluminescence method. The antibody levels of different populations were analyzed.

Results A total of 620 subjects were included， 586 of whom （241 males and 345 females） met the study conditions. There were 90 people in the full vaccination + infection group， 224 people in the intensive vaccination + infection group， and 272 people in the unvaccinated + infection group. The positive rates of COVID-19 antibody in the three groups were 94.44% （95%CI： 87.51%‒98.17%）， 95.98% （95%CI：92.51%‒98.15%） and 22.06% （95%CI： 17.28%‒27.46%）， respectively. The positive rates in full vaccination + infection group and intensive vaccination + infection group was significantly higher than that in unvaccinated + infection group （χ²=147.561，P<0.01；χ²=271.729，P<0.01）. The antibody level in full vaccination + infection group （640.74 AU·mL^-1） and intensive vaccination + infection group （1 200.88 AU·mL^-1） was significantly higher than that in unvaccinated + infection group （4.51 AU·mL^-1） （all P<0.01）.The antibody level in the intensive vaccination + infection group was also significantly higher than that in the whole vaccination + infection group （P < 0.05）.

Conclusion After 5‒6 months of infection， the neutralizing antibody positive rate and antibody level were significantly higher in the elderly who received the full vaccination and infection or intensive vaccination and infection. It is recommended that elderly individuals， who have been infected for more than 5‒6 months but have not been vaccinated， should consider getting vaccinated to enhance their levels of neutralizing antibodies.