Antibody response after a single dose of ChAdOx1-nCOV (Covishield) vaccine in subjects with prior SARS-CoV2 infection: Is a single dose sufficient?

It is crucial to know whether a single dose of vaccine against SARS-CoV-2 is sufficient to elicit immune response in previously infected people in India. A total of 121 participants (baseline seropositive 46 and seronegative 75) were included to study the immune response to ChAdOx1-nCOV (Covishield) vaccine in previously infected or uninfected people. IgG antibodies were estimated at three different time intervals, i.e. pre-vaccination, 25-35 days post 1st vaccination and 25-35 days post 2nd vaccination. The IgG antibody titre was significantly high among previous seropositive subjects with single dose of vaccine compared to seronegative group with both doses of vaccine respectively (4.59{+/-}1.04 vs 3.08{+/-}1.22, p-value: <0.0001). In conclusion, a single dose of Covishield(R) vaccine might be sufficient to induce an effective immune responsein subjects with prior SARS-CoV2 infection. Stratifying vacinees based on their SARS-CoV2 IgG antibody titre before vaccination would help in meeting the increasing vaccine demand and could be effective to circumvent further wave of the pandemic in India.