Clinical and immune response characteristics among vaccinated persons infected with SARS-CoV-2 delta variant: a retrospective study

Abstract

Objectives: This study aimed to observe the clinical and immune response characteristics of vaccinated persons infected with the delta variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in Yangzhou, China.

Methods: We extracted the medical data of 129 patients with delta-variant infection who were admitted to Northern Jiangsu People's Hospital (Yangzhou, China) between August and September, 2021. The patients were grouped according to the number of vaccine doses received into an unvaccinated group: a one-dose group and a two-dose group. The vaccine used was SARS-CoV-2-inactivated vaccine developed by Sinovac. We retrospectively analyzed the patients' epidemiological, clinical, laboratory, and imaging data.

Results: Almost all patients with delta-variant infection in Yangzhou were elderly, and patients with severe/critical illness were over 70 years of age. The rates of severe/critical illness (P=0.006), fever (P=0.025), and dyspnea (P=0.045) were lower in the two-dose group than in the unvaccinated group. Compared to the unvaccinated group, the two-dose group showed significantly higher lymphocyte counts and significantly lower levels of C-reactive protein (CRP), interleukin-6 (IL-6), and D-dimer during hospitalization and a significantly higher positive rate of immunoglobulin G (IgG) antibodies at admission (all P<0.05). The cumulative probabilities of hospital discharge and negative virus conversion were also higher in the two-dose group than in the unvaccinated group (P<0.05).

Conclusions: Two doses of the SARS-CoV-2-inactivated vaccine were highly effective at limiting symptomatic disease and reducing immune response, while a single dose did not seem to be effective.

Keywords: Delta variant; Hospitalization; Immune response; Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2); Vaccine.

Fig. 1. Patients and flow chart. COVID-19: coronavirus disease 2019.

Fig. 2. Distribution of time intervals from onset to admission, onset to diagnosis, and admission to diagnosis. (a‒c) Estimated distributions of the time intervals from onset to admission (a), onset to diagnosis (b), and admission to diagnosis (c) stratified by the number of vaccine doses. (d‒f) Time from onset to admission (d), onset to diagnosis (e), and admission to diagnosis (f) in the unvaccinated, one-dose, and two-dose groups. Data are expressed as mean±SD. One-way ANOVA followed by post-hoc Tukey's test: F _{(2, 126)}=1.96 (d), F _{(2, 126)}=1.04 (e), F _{(2, 126)}=1.75 (f). Unvaccinated group, n=56; one-dose group, n=38; and two-dose group, n=35. SD: standard deviation; ANOVA: analysis of variance.

Fig. 3. Lymphocyte count and CRP, IL-6, and D-dimer levels in the unvaccinated, one-dose, and two-dose groups at 7 and 14 d after admission. (a) Lymphocyte counts on Day 7. Compared with the unvaccinated group, the two-dose group had a higher lymphocyte count. (b‒d) Levels of CRP (b), IL-6 (c), and D-dimer (d) on Day 7. (e) Lymphocyte count remained higher in the two-dose group than in the unvaccinated group on Day 14. (f‒h) Levels of CRP (f), IL-6 (g), and D-dimer (h) on Day 14. Data are expressed as mean±SD. ^* P<0.05, ^** P<0.01, and ^*** P<0.001. One-way ANOVA followed by post-hoc Tukey's test: F _{(2, 126)}=2.40 (a), F _{(2, 126)}=8.34 (b), F _{(2, 126)}=8.34 (c), F _{(2, 126)}=5.06 (d), F _{(2, 82)}=2.42 (e), F _{(2, 82)}=1.55 (f), F _{(2, 82)}=0.73 (g), and F _{(2, 82)}=1.25 (h). At 7 d after admission: unvaccinated group, n=56; one-dose group, n=38; and two-dose group, n=35. At 14 d after admission: unvaccinated group, n=41; one-dose group, n=24; and two-dose group, n=20. CRP: C-reactive protein; IL-6: interleukin-6; SD: standard deviation; ANOVA: analysis of variance.

Fig. 4. Prevalences of immunoglobulin M (IgM) and IgG antibodies in the unvaccinated, one-dose, and two-dose groups after admission: (a‒c) IgM antibodies at 0 (a), 7 (b), and 14 d (c) after admission; (d‒f) IgG antibodies at 0 (d), 7 (e), and 14 d (f) after admission.

Fig. 5. Comparison of immunoglobulin M (IgM) and IgG antibody levels in the unvaccinated, one-dose, and two-dose groups after admission: (a‒c) IgM levels at 0 (a), 7 (b), and 14 d (c) after admission; (d‒f) IgG levels at 0 (d), 7 (e), and 14 d (f) after admission. Data are expressed as mean±SD. ^* P<0.05. One-way ANOVA followed by post-hoc Tukey's test: F _{(2, 126) ‍} =0.26 (a), F _{(2, 126) ‍} =0.34 (b), F _{(2, 82) ‍} =0.72 (c), F _{(2, 126) ‍} =3.51 (d), F _{(2, 126) ‍} =3.12 (e), and F _{(2, 82) ‍} =0.90 (f). At 0 and 7 d after admission: unvaccinated group, n=56; one-dose group, n=38; and two-dose group, n=35. At 14 d after admission: unvaccinated group, n=41; one-dose group, n=24; and two-dose group, n=20. SD: standard deviation; ANOVA: analysis of variance.

Fig. 6. Abnormal chest CT changes in the unvaccinated, one-dose, and two-dose groups. (a, b) Estimated distributions of time intervals from onset to progression (a) and onset to absorption (b) of chest CT abnormalities stratified by the number of vaccine doses. (c) Time interval from onset to absorption of CT abnormalities in the unvaccinated, one-dose, and two-dose groups. Data are expressed as mean±SD. One-way ANOVA followed by post-hoc Tukey's test: F _{(2, 126)}=1.76. Unvaccinated group, n=56; one-dose group, n=38; and two-dose group, n=35. CT: computed tomography; SD: standard deviation; ANOVA: analysis of variance.

Fig. 7. Hospital discharge rates and factors associated with clinical outcomes in the unvaccinated, one-dose, and two-dose groups. (a, b) Probabilities of hospital discharge and length of hospitalization stratified by vaccine doses. (c) Results of proportional hazard Cox model. Hazard ratios and corresponding 95% confidence intervals are shown for the following factors: age, sex, fever, and levels of C-reactive protein, interleukin-6 (IL-6), D-dimer, total bilirubin, alanine aminotransferase, and creatinine.

Fig. 8. Positive viral RNA rates and factors associated with negative virus conversion in the unvaccinated, one-dose, and two-dose groups. (a, b) Positive rate of viral RNA detection and time until negative virus conversion after diagnosis, stratified by vaccine doses. (c) Results of proportional hazard Cox model. Hazard ratios and corresponding 95% confidence intervals are shown for the following factors: age, sex, fever, and levels of C-reactive protein, interleukin-6 (IL-6), D-dimer, total bilirubin, alanine aminotransferase, and creatinine.