Objectives: Research on recovering COVID-19 patients could be helpful for containing the pandemic and developing vaccines, but we still do not know much about the clinical features, recovery process, and antibody reactions during the recovery period. Methods: We retrospectively analysed the epidemiological information, discharge summaries, and laboratory results of 324 patients. Results: In all, 15 (8.62%) patients experienced chest distress/breath shortness, where 8 of the 15 were severely ill. This means severely ill patients need an extended amount of time to recover after discharge; next, 20 (11.49%) patients experienced anxiety and 21 (12.07%) had headache/insomnia and a small fraction of them complained of anosmia/ageusia, indicating that these patients need treatment for mental and psychological health issues. Regarding the re-positive patients, their CT and laboratory test results showed no obvious evidence of illness progress or infectivity but a high anti-SARS-CoV-2 antibody expression. Conclusion: Recovered COVID-19 patients need psychological and physiological care and treatment, re-positivity can occur in any person, but juveniles, females, and patients with mild/moderate existing symptoms have higher rates of re-positivity, While there is no evidence that turning re-positive has an impact on their infectivity, but it still alerted us that we need differentiate them in the following managements.

Background: The second wave of the coronavirus disease 2019 (COVID-19) epidemic in India was caused by the COVID-19 Delta variant. However, the epidemiological characteristics and transmission mechanism of the Delta variant remain unclear. To explore whether the epidemic trend will change after effective isolation measures were taken and what is the minimum number of individuals who need to be vaccinated to end the epidemic.Methods: We used actual data from March 5 to April 15, 2021, of daily updates confirmed cases and deaths, to estimate the parameters of the model and predict the severity of possible infection in the coming months. The classical Susceptible-Exposed-Infected-Removed (SEIR) model and extended models [Susceptible-Exposed-Infected-Removed-Quarantine (SERIQ) model and Susceptible-Exposed-Infected-Removed- medicine (SERIM) model] were developed to simulate the development of epidemic under the circumstances of without any measures, after effective isolation measures were taken and after being fully vaccinated.Results: The result demonstrated good accuracy of the classic model. The SEIRQ model showed that after isolation measures were taken, the infections will decrease by 99.61% compared to the actual number of infections by April 15. And the SEIRQ model demonstrated that if the vaccine efficative rate was 90%, when the vaccination rate was 100%, the number of existing cases would reach a peak of 529,723 cases on the 52nd day.Conclusion: Effective quarantine measures and COVID-19 vaccination from official are critical prevention measures to help end the COVID-19 pandemic.

Nucleic acid testing and antibody testing data from 143 recovered COVID-19 patients during the convalescent phase were retrospectively analyzed. A total of 23 (16.1%) recovered patients re-tested positive for SARS-CoV-2 RNA by RT-PCR. Three months after symptom onset, 100% and 99.3% of the patients remained positive for total and IgG antibodies, and the antibody levels remained high. IgM antibodies declined rapidly, with a median time to seroconversion of 67 (95% CI: 59, 75) days after onset. Approximately 25% of patients were seronegative for IgA antibodies at three months after onset. There was no statistically significant difference in antibody kinetics between patients with and without re-positive RT-PCR results during the convalescent phase. Supplementary Information The online version contains supplementary material available at 10.1007/s00705-021-05132-9.