Long-term antibody response after COVID-19 vaccination in health care workers: A single centre study from Pakistan.

The retrospective cohort study was planned to determine long-term anti-spike immunoglobulin G levels after receiving coronavirus disease-2019 vaccination by healthcare workers. The study took place between June and July 2022 at the Indus hospital in Karachi. Healthcare workers who had previously screened negative to prevaccination Severe Acute Respiratory Syndrome Coronavirus 2 nucleocapsid antibodies were tested for post-vaccination Severe Acute Respiratory Syndrome Coronavirus 2 anti-spike immunoglobulin G levels using a quantitative assay. The test was also performed on the stored pre-vaccination samples of the subjects collected up to 18 months previously. Antibody levels in subjects without infection, with infection and with booster administration were compared. The median postvaccination anti-spike immunoglobulin G in infected only, infected with routine vaccination and infected with booster values were 1,725.6 IU/mL (interquartile range: 684.80- 4,708.9 IU/mL), 2,067.15 IU/mL (interquartile range: 705.33-4,670.4 IU/mL) and 6,139.15 IU/mL (interquartile range: 2,426.05-10,623.40 IU/mL). There was a doubling of antibody titers, from 1,744 IU/mL to 3,829 IU/mL, in those who received a booster versus routine vaccination (p>0.05). The antibodies remained positive more than a year following vaccination.