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Background & objectives: Vaccination against COVID-19 induces spike protein-binding IgG antibodies, a robust correlate of protection against COVID-19. This study was undertaken to assess the humoral response after completion of both the doses of ChAdOx1 nCoV vaccine in healthcare workers (HCWs) at a tertiary care health centre in India. Methods: A cross-sectional COVID-19 vaccine-induced antibody study was conducted among HCWs. IgG antibodies against spike protein were measured at least 28 days after the first dose and the second dose of vaccination in both SARS CoV-2 naïve and recovered HCWs. Mean and median antibody titre following each dose of vaccine and its association with age, gender, co-morbidities and factors such as exercise, stress and sleep deprivation were also explored. Results: Among the 200 vaccine recipients, 91.5 per cent showed seroconversion after the first dose and 99.5 per cent after the second dose. The mean titre after the second dose was significantly higher when compared to the first dose (12.68±4.17 vs. 9.83±6.3, P=0.001). More than half (54%) had high antibody titre ?12 S/Co (Signal/cut-off). Previous COVID-19 infection was the single most important factor influencing antibody production, where the mean titre just after a single dose [mean-17.81±5.94, median-20.5 (interquartile range [IQR]-3.7)] surpassed the titre after the second dose in SARS CoV-2 naïve individuals [mean-12.29±4.00, median-12.8 (IQR-3.7), P=0.001]. Furthermore, 28 per cent of vaccinees showed a reduction in titre after the second dose. The mean fall in titre was 2.25±1.40 and was more pronounced in males, the younger age group and those with previous COVID-19 infection. Interpretation & conclusions: ChAdOx1 nCov-19 vaccine after two doses elicited an excellent immune response. However, greater immunogenicity after the first dose was seen among those with previous COVID-19 infection, even surpassing the titre achieved by the second dose of vaccine in SARS CoV-2 naïve recipients. A fall in antibody titre after the second dose is a matter of concern and requires further studies.
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Objective To analyze the changes of serum antibody levels of children in Changning District of Shanghai City, who received the second dose of varicella vaccine at one year after the first dose thereof.Methods A total of 206 children aged at 1 to 3 years in Changning District who had received one dose of varicella vaccine were included as objects of observation in the observation group.They received the second dose of varicella vaccine at one year after the first dose thereof.Their venous blood was collected before the second dose thereof as well as and at 35 to 42 days thereafter, and the varicella antibody level was tested through Fluorescent Antibody to Membrane Antigen(FAMA) assay so as to compare the difference between the antibody level before the second dose of varicella vaccine and that thereafter.Results The varicella-zoster virus(VZV) antibody titers of the blood serum before and after the second dose of varicella vaccine for the objects of observation were compared.The geometric mean titers(GMT) of the antibody before and after the second dose of varicella vaccine were 1∶11.90 and 1∶71.04, respectively, with the antibody level of the latter significantly higher than that of the former (t=18.1, P<0.01), which showed significant difference between the two.The objects of observation whose antibody levels increased to over 4 times their original antibody levels occupied 82.52% of the total objects of obervation.Conclusion The second dose of varicella vaccine received at one year after the first dose thereof can effectively improve the VZV antibody titer in the blood serum of immunization recipients.
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Objective: To evaluate the effect of the second dose of measles vaccine on measles antibody status during childhood. Setting: Immunization centre of Under-five Clinic of the Department of Community Medicine at a tertiary-hospital. Design: Randomized Controlled trial. Methods: Blood samples were collected from all subjects for baseline measles serology by heel puncture at 9-12 months of age. All subjects were given the first dose of measels vaccine. At second visit (3-5 months later), after collecting the blood sample from all, half the children were randomized to receive the second dose of measles vaccine (study group), followed by collection of the third sample six weeks later in all the subjects. Results: A total of 78 children were enrolled and 30 children in each group could be analyzed. 11(36.6%) children in the study group and 13 (43.3%) children in the control group had protective levels of measles IgG at baseline. Around 93.3 % of children in the study group had protective measles antibody titers as against 50% in the control group at the end of the trial. The Geometric Mean Titre (GMT) of measles IgG increased from 14.8 NTU/mL to 18.2 NTU/mL from baseline to six weeks following receipt of the second dose of the vaccine in the study group, as compared to a decrease from 16.8 NTU/mL to 12.8 NTU/mL in the control group. Conclusions: A second dose of measles vaccine boosts the measles antibody status in the study population as compared to those who receive only a single dose.