ABSTRACT
SARS-CoV-2 inactivated vaccines have shown remarkable efficacy in clinical trials, especially in reducing severe illness and casualty. However, the waning of humoral immunity over time has raised concern over the durability of immune memory following vaccination. Thus, we conducted a nonrandomized trial among the healthcare workers (HCWs) to investigate the long-term sustainability of SARS-CoV-2-specific B cells and T cells stimulated by inactivated vaccines and the potential need for a third booster dose. Although neutralizing antibodies elicited by the standard two-dose vaccination schedule dropped from a peak of 29.3 arbitrary units (AU)/mL to 8.8 AU/mL 5 months after the second vaccination, spike-specific memory B and T cells were still detectable, forming the basis for a quick recall response. As expected, the faded humoral immune response was vigorously elevated to 63.6 AU/mL by 7.2 folds 1 week after the third dose along with abundant spike-specific circulating follicular helper T cells in parallel. Meanwhile, spike-specific CD4+ and CD8+ T cells were also robustly elevated by 5.9 and 2.7 folds respectively. Robust expansion of memory pools by the third dose potentiated greater durability of protective immune responses. Another key finding in this trial was that HCWs with low serological response to two doses were not truly "non-responders" but fully equipped with immune memory that could be quickly recalled by a third dose even 5 months after the second vaccination. Collectively, these data provide insights into the generation of long-term immunological memory by the inactivated vaccine, which could be rapidly recalled and further boosted by a third dose.
ABSTRACT
Objective The time and the risk factors of virus nucleic acids negative conversion of coronavirus disease 2019 (COVID-19) patients were analyzed. Methods The clinical data of patients with COVID-19 admitted to Chongqing Public Health Medical Treatment Center from February 6 to March 9, 2020 were collected retrospectively. The clinical characteristics, treatment and outcome were described. The time of turning negative of nucleic acid was counted and the risk factors of turning negative of nucleic acid were analyzed. Results There were 104 confirmed cases of COVID-19, 56 males and 48 females, with an average age of (49.9 +or- 15.5) years (12-86 years old). The average interval between clinical symptoms and medical treatment was 5.5 days. From the time point of clinical symptoms, the time needed for nucleic acid to turn negative was (19.8 +or- 7.7) days, of which 32 cases (30.8%) turned negative within 14 days, 72 cases (69.2%) turned negative more than 14 days, and 14 cases (13.5%) turned negative more than 28 days. Univariate analysis showed that the time interval from clinical symptoms to medical treatment (6.7+or-4.4) days of nucleic acid conversion group after 14 days was longer than that (2.6 +or-1.8) days of conversion group within 14 days (P < 0.05);the incidence of combined with pulmonary bacterial infection (25 cases, 34.7%), infection more than three pulmonary lobes (36 cases, 50.0%), severe patients (24 cases, 33.3%) and combined use of glucocorticoids were greater than those of conversion group within 14 days (all P < 0.05). Multivariate analysis showed that there were significant differences in the time interval from symptoms to medical treatment and the proportion of three or more lobes involved in lung lesions between the two groups (P < 0.05). Conclusions The risk factors of viral nucleic acid turning negative are the timeliness of medical treatment, combined with pulmonary bacterial infection, wide range of pulmonary lesions, clinical typing and combined use of glucocorticoids, especially the timeliness of medical treatment and the range of pulmonary lesions.