Sequential Observation of Antibody Response Pattern at 3 and6 Months Following ChAdOx1 nCoV-19 Vaccination AmongHealth Care Workers-A Prospective Single Cohort Study

Background: the duration of the immune response induced by chadox1 ncov-19 vaccinationin a real-world setting is unknown.objectives: this study is aimed to estimate the 6-month trend of sars-cov-2 antibody titerafter covishield vaccination among health care workers (hcw) and their associated factors.materials & methods: a prospective single cohort study of health care workers was done ina tertiary care-teaching institute of central kerala from january 2021 to october 2021. hcwswho have given pre-vaccination serum sample for sars-cov-2 antibody estimation andnegative for sars-cov-2 antibody were included. they were followed up and their bloodsamples to check for antibody levels were taken 28 days after first dose, 2 weeks after seconddose, and 3 and 6 months after first dose of chadox1 ncov-19 vaccine. samples taken from 102hcw were sent for sars-cov-2 igg antibody testing.results: mean age of the study participants was 39.3 (age range:19 - 71) yrs. and 71.6% werefemales. antibody levels of participants at 3rd month ranged from 0.28 s/c to 21.2 s/c with amean of 8.01. only 34 (33.3%) hcw had igg antibody levels >9.5 s/c. mean antibody levelfurther declined to 6.09 s/c at 6th month. only 19 (28.4%) had antibody levels more than 9.5s/c at 6th month. hcw with aged less than 50 years and those who had covid disease during the study period had a significantly higher level of igg antibody titres. quantitative results werereported as signal to cut-off (s/c) value.conclusion: the study found that after vaccination with covishield vaccine igg levels peakedat 14 days following second dose of vaccine, then getting decreased in the third month and furtherin sixth month confirming the need for a booster dose. covid antibody levels were significantlyhigher in covid infected hcw and in young age participants.