Persistence of immune responses to the Sinopharm/BBIBP-CorV vaccine.
Jeewandara C., Aberathna IS., Pushpakumara PD., Kamaladasa A., Guruge D., Wijesinghe A., Gunasekera B., Ramu ST., Kuruppu H., Ranasinghe T., Dayarathna S., Dissanayake O., Gamalath N., Ekanayake D., Jayamali J., Jayathilaka D., Dissanayake M., Jayadas TT., Mudunkotuwa A., Somathilake G., Harvie M., Nimasha T., Danasekara S., Wijayamuni R., Schimanski L., Rijal P., Tan TK., Dong T., Townsend A., Ogg GS., Malavige GN.
BackgroundTo determine the kinetics and persistence of immune responses following the Sinopharm/BBIBP-CorV, we investigated immune responses in a cohort of Sri Lankan individuals.MethodsSARS-CoV-2 specific total antibodies were measured in 20-39 years (n = 61), 40-59 years (n = 120) and those >60 years of age (n = 22) by enzyme-linked immunosorbent assay, 12 weeks after the second dose of the vaccine. Angiotensin-converting enzyme 2 (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.ResultsA total of 193/203 (95.07%) of individuals had detectable SARS-CoV-2 specific total antibodies, while 67/110 (60.9%) had ACE2R-Ab. A total of 14.3%-16.7% individuals in the 20-39 age groups had detectable antibodies to the RBD of the WT and variants of concern, while the positivity rates of those ≥60 years of age was <10%. A total of 14/49 (28.6%) had Interferon 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 from 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 40-59 (p = .0007) and ≥60 (p = .005) age groups.ConclusionsAntibody 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.