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A total of 125 confirmed COVID-19 cases were studied to assess the NAb response in a variety of patients with differing symptoms. As shown in Table 1, 4 (3.2%) were classified as mild cases based on their clinical manifestations, 81 (64.8%) were moderate, 33 (26.4%) were severe, and the remaining 7 (5.6%) were critical cases. Males and females were equally distributed regarding their clinical classification (χ2 = 2.21, P = 0.529). The average age of these patients was 53.4 years, ranging from 19 to 90. Oxygen supplementation was required in most cases (72%), with nine cases (7.2%) requiring mechanical ventilation or extracorporeal membrane oxygenation (ECMO). The average hospital duration for patients was 26.2 days, with a 95% confidence interval (CI) of 24.5 to 27.8 for cases who had been discharged. The symptoms of the mild cases [12 days post-onset (dpo)] lasted a significantly shorter time than those of the moderate (24 dpo) and severe (31 dpo) cases.
Characteristic Clinical classification Total Mild case Moderate case Severe case Critical cases Sex, n (%) Male 1 (1.47) 44 (64.71) 18 (26.47) 5 (7.35) 68 (100.00) Female 3 (5.26) 37 (64.91) 15 (26.32) 2 (3.51) 57 (100.00) Age (years) 40.5 ± 15.4 51.3 ± 14.8 56.0 ± 12.5 72.4 ± 8.0 53.4 ± 15.0 ≤ 60, n (%) 3 (3.80) 55 (69.62) 21 (26.58) 0 (0) 79 (100.00) > 60, n (%) 1 (2.17) 26 (56.52) 12 (26.09) 7 (15.22) 46 (100.00) Underlying disease, n (%) No disease 2 (2.94) 48 (70.59) 14 (20.59) 4 (5.88) 68 (100.00) ≥ One disease 2 (3.51) 33 (57.89) 19 (33.33) 3 (5.26) 57 (100.00) Oxygen supplement requirement, n (%) No requirement 3 (8.57) 32 (91.43) 0 (0) 0 (0) 35 (100.00) Low flow oxygen 1 (1.72) 48 (82.76) 9 (15.52) 0 (0) 58 (100.00) High flow oxygen 0 (0) 1 (4.35) 22 (95.65) 0 (0) 23 (100.00) Mechanical ventilation 0 (0) 0 (0) 2 (40.00) 3 (60.00) 5 (100.00) ECMOa 0 (0) 0 (0) 0 (0) 4 (100.00) 4 (100.00) Disease duration (days) 12.3 ± 5.9 24.5 ± 8.0 31.2 ± 7.8 39.4 ± 24.3 26.7 ± 10.5 ≤ 21, n (%) 4 (10.00) 30 (75.0) 3 (7.50) 3 (7.50) 40 (100.00) > 21, n (%) 0 (0) 51 (60.00) 30 (35.29) 4 (4.71) 85 (100.00) Note. aECMO, Extracorporeal membrane oxygenation. Table 1. Characteristics of the COVID-19 patients in this study
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The proportion of RNA-positive patients declined gradually (Figure 1) with a median of 15 dpo, while the duration of RNA-positivity in severe patients was significantly longer (P < 0.001) than in patients with moderate symptoms. However, no significant difference was observed in the sex, age, and underlying disease classifications. The proportion of seropositive patients continuously increased and reached 100% after 21 dpo of symptoms.
Figure 1. RNA-positive levels and the kinetics of NAbs in COVID-19 patients over time. UD, underlying diseases
Meanwhile, NAb levels increased, peaked at approximately 20–30 dpo, and then decreased as symptoms abated with three different trends detected: 1. stable type, 2. drop type, and 3. wave type (Figure 1 & Table 2) trends. As the NAb testing period may interfere with variability, 51 follow-up cases were selected to study the changes in NAbs. A total of 18 cases (35.3%) showed a stable-type trend since their NAb titers continuously increased or were maintained at a stable level after the peak; 26 cases (51.0%) showed a drop-type trend where NAb expression decreased by at least four times compared with their peak titer; and 7 cases (13.7%) showed a large fluctuation in NAb levels. However, there was no significant difference in trend types between each classification (Table 2). Among all of the cases, six cases older than 60 years and one case that was 58 years showed a wave-type trend, indicating that this type of trend may be associated with older patients. Moreover, the NAb levels of a severe patient were lower than 1:4 in the last antibody test at 56 dpo.
Characteristic Neutralizing antibody trend, n (%) Total χ2 P value Rising type Drop type Wave type Sex 4.46 0.094 Male 8 (26.67) 19 (63.34) 3 (10.00) 30 Female 10 (47.62) 7 (33.33) 4 (19.05) 21 Age (years) 4.73 0.089 ≤ 60 11 (40.74) 15 (55.56) 1 (3.70) 27 > 60 7 (29.17) 11 (45.83) 6 (25.00) 24 Underlying disease 1.89 0.430 No disease 8 (33.33) 11 (45.83) 5 (20.83) 24 ≥ One disease 10 (37.04) 15 (55.56) 2 (7.41) 27 Clinical classification 3.92b 0.166 Mild case 2 (66.67) 1 (33.33) 0 (0) 3 Moderate case 11 (37.93) 16 (55.17) 2 (6.90) 29 Severe case 5 (29.41) 7 (41.18) 5 (29.41) 17 Critical case 0 (0) 2 (100.00) 0 (0) 2 Note. aThere was no statistical difference in the final testing times for each classification. bOnly moderate and severe cases were compared. Table 2. Distribution of neutralizing antibody trends in each classificationa
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We further analyzed the NAb levels of each group at two time points: the initial detection of NAb formation and the peak titer of NAbs. As the enrollment of patients and serum sampling times were not planned or predictable, the first NAb-positive serum of a patient collected after 10 dpo may interfere with the estimation of the first day of detection of NAb. Therefore, 104 cases were analyzed to estimate the initial day of NAb formation (10.4 ± 5.2 dpo). Peak NAb titers were based on 121 cases (20.8 ± 10.0 dpo), with mild cases that were discharged before their NAb levels reached their peak being omitted from the analysis. Follow-up tests were performed for 51 patients with NAbs, and NAbs were still detectable in one case at 85 dpo with a titer of 1:8.
There was no significant difference between each classification in both NAb levels and the time of initial detection of antibody formation indicating a similar response of NAbs to SARS-CoV-2 (Figure 2). The peak NAb titer in males was slightly higher than that in females (P = 0.019), and the geometric means of the antibody titer were 1:163.14 and 1:101.83, respectively. The peak level of NAbs between each disease severity type was significantly different (P < 0.001); the levels in severe patients were the highest, with a geometric mean antibody titer of 1:272.48, followed by moderate patients with a mean titer of 1:115.36. In addition, the time taken to reach peak NAb titer in severe cases was slightly longer than in moderate cases (Figure 2).
Figure 2. Differences in initial and peak NAb titers against SARS-CoV-2 in patients varying in sex, disease severity, age stratification, and underlying disease status. (A)–(D) Initial NAb levels; (E)–(H) Day(s) post-onset of initial NAb formation; (I)–(L) Highest NAb levels; (M)–(P) Day(s) post-onset to reach the highest NAb levels. Statistical significance was determined using the Student’s t-test (E–H and M–P), Mann–Whitney U test (A, C, D, I, K, L), or Kruskal–Wallis H test (B, F, J, N). *, P < 0.05; ***, P < 0.001.
As sex and disease levels showed a discrepancy in the peak NAb levels, we further classified these cases into four groups based on sex and age: younger or equal to 60 years of age, and older than 60 years of age (younger males, MY; younger females, FY; elder males, ME; elder females, FE). The MY group showed higher NAb levels than the FY and FE groups, suggesting that younger men have the fastest response to SARS-CoV-2 (Figure 3).
Figure 3. Differences in the peak titer levels, days required to reach peak NAb levels, and disease duration between different sex/age groups. MY, males ≤ 60 years old; ME, males > 60 years old; FY, females ≤ 60 years old; FE, females > 60 years old. Green dots represent mild cases and yellow dots represent severe cases. Statistical significance was determined using the Student’s t-test and Mann–Whitney U test. a–i, indicates a statistically significant difference (P < 0.05) between groups that have the same letter in each graph. *, P < 0.05; **, P < 0.01.
In addition, severe cases younger than 60 years of age had higher NAb levels than mild cases; however, this trend was not observed for older patients. The MY and FY groups reached peak Nab levels quickly and were discharged, whereas no difference was observed for the ME and FE groups, indicating that older patients experience weaker responses to SARS-CoV-2, thereby prolonging the disease duration.
Kinetic Characteristics of Neutralizing Antibody Responses Vary among Patients with COVID-19
doi: 10.3967/bes2021.133
- Received Date: 2021-09-03
- Accepted Date: 2021-11-24
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Key words:
- Sex /
- Kinetics /
- Neutralizing antibody /
- SARS-CoV-2
Abstract:
Citation: | LI Ling Hua, TU Hong Wei, LIANG Dan, WEN Chun Yan, LI An An, LIN Wei Yin, HU Ke Qi, HONG Wen Shan, LI Yue Ping, SU Juan, ZHAO San Tao, LI Wei, YUAN Run Yu, ZHOU Ping Ping, HU Feng Yu, TANG Xiao Ping, KE Chang Wen, KE Bi Xia, CAI Wei Ping. Kinetic Characteristics of Neutralizing Antibody Responses Vary among Patients with COVID-19[J]. Biomedical and Environmental Sciences, 2021, 34(12): 976-983. doi: 10.3967/bes2021.133 |