Persistence of antibody and T cell responses to the Sinopharm/BBIBP-CorV vaccine in Sri Lankan individuals

Jeewandara, C.; Aberathna, I.; Pushpakumara, P.; Kamaladasa, A.; Guruge, D.; Wijesinghe, A.; Gunasekara, B.; Tanussiya, S.; Kuruppu, H.; Ranasinghe, T.; Dayarathna, S.; Dissanayaka, O.; Gamalath, N.; Ekanayaka, D.; Jayamali, J.; Jayathilaka, D.; Dissanayaka, M.; Jayadas, T.; Mudunkotuwa, A.; Somathilaka, G.; Harvie, M.; Nimasha, T.; Danasekara, S.; Wijayamuni, R.; Schimanski, L.; Rijal, P.; Tan, T.; Dong, T.; Townsend, A.; Ogg, G.; Malavige, G. N.

Background: To determine the kinetics and persistence of immune responses following the Sinopharm/BBIBP-CorV, we investigated immune responses in a cohort of Sri Lankan individuals. Methods: SARS-CoV-2 specific total antibodies were measured in 20-to-39 year (n=61), 40-to-59-year and those >60 years of age (n=22) by ELISA, 12 weeks after the second dose of the vaccine. ACE2 receptor blocking antibodies (ACE2R-Ab), antibodies to the receptor binding domain (RBD) of the ancestral virus (WT) and variants of concern, were measured in a sub cohort. T cell responses and memory B cell responses were assessed by ELISpot assays. Results: 193/203 (95.07%) of individuals had detectable SARS-CoV-2 specific total antibodies, while 67/110 (60.9%) had ACE2R-Ab. 14.3% to 16.7% individuals in the 20 to 39 age groups had detectable antibodies to the RBD of the WT and VOC, while the positivity rates of those >60 years of age was <10%. 14/49 (28.6%) had IFN{gamma} ELISpot responses to overlapping peptides of the spike protein, while memory B cell responses were detected in 9/20 to the S1 recombinant protein. The total antibody levels and ACE2R-Ab declined after 2 to 12 weeks from the second dose, while ex vivo T cell responses remained unchanged. The decline in ACE2R-Ab levels was significant among the 40 to 59 (p=0.0007) and [≥]60 (p=0.005) age groups. Conclusions: Antibody responses declined in all age groups, especially in those >60 years, while T cell responses persisted. The effect of waning of immunity on hospitalization and severe disease should be assessed by long term efficacy studies.