Abstract
BackgroundAlthough effective vaccines have been developed against coronavirus disease 2019 (COVID-19), the level of neutralizing antibodies (NAbs) induced after vaccination in the real world is still unknown. The aim of this work was to evaluate the level and persistence of NAbs induced by two inactivated COVID-19 vaccines in China.MethodsSerum samples were collected from 1,335 people aged 18 years and over who were vaccinated with an inactivated COVID-19 vaccine at Peking University People’s Hospital from January 19 to June 23, 2021, for the detection of anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies.ResultsThe positive rate for NAbs against SARS-CoV-2 was 79–91% from the first month to the second month after the second vaccine dose. The gradual decline in positivity rate for NAb response was observed from 78% at 3 months post-vaccination to 0% at 12 months post-vaccination. When there was a 21-day interval between the two doses of vaccine, the NAb positivity rate was 0% 6 months after the second dose. NAb levels were significantly higher when the interval between two doses were 3–8 weeks than when it was 0–3 weeks (χ2 = 14.04, p < 0.001). There was a linear correlation between NAbs and IgG antibodies in 1,335 vaccinated patients. NAb levels decreased in 31 patients (81.6%) and increased in 7 patients (18.4%) over time in the series of 38 patients after the second vaccination. The NAb positivity rate was significantly higher in 18- to 40-year-old subjects than in 41- to 60-year-old subjects (t = −1.959, p < 0.01; t = 0.839, p < 0.01).ConclusionThe NAb positivity rate was the highest at the first and second month after the second dose of vaccine, and gradually decreased over time. With a 21-day interval between two doses of vaccine, neutralizing antibody levels persisted for only 6 months after the second dose of vaccine. Therefore, a third vaccine dose is recommended. Our results suggest that in cases in which NAbs cannot be detected, IgM/IgG antibodies can be detected instead. The level of NAbs produced after vaccination was affected by age but not by sex. Our results suggest that an interval of 21 to 56 days between shots is suitable for vaccination.
Highlights
The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of novel coronavirus pneumonia [coronavirus disease 2019 (COVID-19)], which has caused a global pandemic
To assess the change in neutralizing antibody (NAb) over time in people who completed the two-dose vaccine, we calculated the median number of days between completing the two-dose vaccine and testing for SARS-CoV-2 antibodies, which was 50 days (0–332 days)
Our research shows that the NAb positivity rate was 66.5% among adults from the 1st to 12th months after receiving two doses of inactivated vaccine and from the 1st to 11th months after receiving one dose of vaccine
Summary
The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of novel coronavirus pneumonia [coronavirus disease 2019 (COVID-19)], which has caused a global pandemic. As virus mutations have been reported recently, an effective vaccine against SARS-CoV2 is urgently needed to control the global COVID-19 pandemic. More than 280 vaccine candidates are in development worldwide, of which 23 are in phase three clinical trials (World Health Organization, 2021). Inactivated vaccines, such as the influenza vaccine, have been widely studied and used to prevent respiratory tract infection due to their good safety (Kyriakidis et al, 2021). A phase 3 clinical trial of inactivated vaccines in China evaluated the efficacy and persistence of immunization by detecting neutralizing antibody (NAb) titers (Al Kaabi et al, 2021). The aim of this work was to evaluate the level and persistence of NAbs induced by two inactivated COVID-19 vaccines in China
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