Comparison of Antibody Response Elicited by ChAdOx1 and BNT162b2 COVID-19 Vaccine

Abstract

Background: ChAdOx1 and BNT162b2 vaccines are currently commonly used against coronavirus disease 2019 worldwide. Our study was designed to determine the serostatus and relative levels of anti-S and neutralizing antibodies in patients who were administered either ChAdOx1 or BNT162b2 vaccine. In addition, we investigated whether the antibody response to each vaccine differed according to sex and age.

Methods: Healthcare workers (HCWs) at a general hospital who were vaccinated with two doses of either ChAdOx1 or BNT162b2 were invited to participate in this prospective cohort study. Blood samples of HCWs vaccinated with both ChAdOx1 doses over a period of 12 weeks were collected at weeks 4 and 8 post first vaccination and 2 weeks post second vaccination. Blood samples of HCWs vaccinated with BNT162b2 were collected in the third week after the first dose, and the second dose was then administered on the same day; two weeks post second dose (5 weeks after the first dose), blood samples were collected to assess the antibody response. The titers of anti-S antibodies against the severe acute respiratory syndrome coronavirus 2 spike (S) protein receptor-binding domain and the neutralizing antibodies in the collected blood were evaluated.

Results: Of the 309 HCWs enrolled in the study, 205 received ChAdOx1 and 104 received BNT162b2. Blood samples from participants receiving either the ChAdOx1 or BNT162b2 vaccine exhibited substantial anti-S and neutralizing antibody seropositivity subsequent to the second dose. All participants (100%) from both vaccine groups were seropositive for anti-S antibody, while 98% (201/205) of ChAdOx1-vaccinated individuals and 100% (104/104) of BNT162b2-vaccinated individuals were seropositive for neutralizing antibodies. The median levels of anti-S and neutralizing antibodies were significantly higher in the BNT162b2-vaccinated group than the ChAdOx1-vaccinated group; in particular, anti-S antibody titers of 1,020 (interquartile range, 571.0-1,631.0) U/mL vs. 2,360 (1,243-2,500) U/mL, P < 0.05, were recorded for the ChAdOx1 and BNT162b2 groups, respectively, and neutralizing antibody titers of 85.0 (65.9-92.1%) vs. 95.8 (94.4-96.6%), P < 0.05, were recorded for the ChAdOx1 and BNT162b2 groups, respectively. In the ChAdOx1 vaccine group, the neutralizing antibody level was significantly higher in women than in men (85.7 [70.3-92.5%] vs. 77.7 [59.2-91.0%], P < 0.05); however, the neutralizing antibody titer in the BNT162b2 vaccine group did not vary between the two sexes (95.9 [95.2-96.6%] vs. 95.2 [93.5-96.3%], P = 0.200). Analysis of the correlation of antibody profiles with age revealed that the levels of anti-S antibodies and signal inhibition rate (SIR) of neutralizing antibodies decreased significantly with age.

Conclusion: Both the ChAdOx1- and BNT162b2-vaccinated groups showed high seropositivity for anti-S and neutralizing antibodies. The SIR of neutralizing antibodies in the ChAdOx1 vaccine group was higher in women than in men. Enhanced antibody responses were observed in participants vaccinated with BNT162b2 compared to those vaccinated with the ChAdOx1 vaccine.

Keywords: Antibody; COVID-19 Vaccine; Immunogenicity; SARS-CoV-2.

Fig. 1. Comparison of antibody responses between ChAdOx1 and BNT162b2 vaccinees. Antibody titers after 1st and 2nd doses of ChAdOx1 and BNT162b2 vaccines are shown.

SIR = signal inhibition rate.

Fig. 2. Antibody responses after 1st and 2nd dose in ChAdOx1 vaccinees. The antibody titers showed no significant difference at 4 and 8 weeks after the first dose but increased markedly after the second dose of ChAdOx1 vaccine.

NS = not significant, SIR = signal inhibition rate.

Fig. 3. The correlation between SARS-CoV-2 anti-S antibodies (U/mL) and neutralization rate (%). SARS-CoV-2 anti-S antibody and neutralizing antibody titers showed a strong positive correlation (Pearson's r = 0.89).

SARS-CoV-2 = severe acute respiratory syndrome coronavirus 2.

Fig. 4. Difference in anti-S titers and neutralizing antibody titers between two sexes. After the 2nd dose of ChAdOx1 vaccine, the neutralizing antibody titer was higher in females than in males. Regarding the BNT162b2 vaccine, after the 1st dose, the levels of anti-S and neutralizing antibodies were higher in females than in males, but there was no difference in the antibody titers between the sexes after the 2nd dose.

NS = not significant, SIR = signal inhibition rate.

Fig. 5. Level of anti-S and neutralizing antibodies according to the age. (A) In ChAdOx1 vaccine group, the neutralizing antibody titer was slightly higher in the younger age group than in older age group after the second dose. In the BNT162b2 group, there was no significant difference in the antibody response according to age after the second dose. (B) For anti-S and neutralizing antibody, the antibody levels of individuals are plotted against patient age in both vaccine groups with the best fit lines, Pearson's correlation (R) and P value (P). In both vaccine groups, neutralization tended to decrease with age.

SIR = signal inhibition rate.