Immune Responses to a Single Dose of the AZD1222/Covishield Vaccine at 16 Weeks in Individuals in Sri Lanka.
Jeewandara C., Guruge D., Pushpakumara PD., Kamaladasa A., Aberathna IS., Ramu ST., Gunasekera B., Wijesinghe A., Dissanayake O., Kuruppu H., Ranasinghe T., Jayathilaka D., Dayarathna S., Ekanayake D., Jayamali J., Gamalath N., Mudunkotiwa A., Somathilake G., Dissanayake M., Harvie M., Nimasha T., Madusanka D., Jayadas T., Wijayamuni R., Schimanski L., Rijal P., Tan TK., Townsend A., Ogg GS., Malavige GN.
Due to limited access to vaccines, many countries have only administered a single dose of the AZD1222, whereas the dosage intervals have increased ≥4 wk. We sought to investigate the immunogenicity of a single dose of vaccine at ≥16 wk postimmunization. Severe acute respiratory syndrome coronavirus 2-specific Abs in 553 individuals and Abs to the receptor-binding domain of the Wuhan virus (wild-type) and the variants of concern, angiotensin-converting enzyme 2 receptor blocking Abs ex vivo and cultured IFN-γ T cell (Homo sapiens) responses and B cell (H. sapiens) ELISPOT responses, were investigated in a subcohort. The seropositivity rates in those >70 y of age (93.7%) was not significantly different compared with other age groups (97.7-98.2; Pearson χ2 = 7.8; p = 0.05). The Ab titers (Ab index) significantly declined (p < 0.0001) with increase in age. A total of 18 of 69 (26.1%) of individuals did not have angiotensin-converting enzyme 2 receptor-blocking Abs, whereas responses to the receptor-binding domain of wild-type (p = 0.03), B.1.1.7 (p = 0.04), and B.1.617.2 (p = 0.02) were significantly lower in those who were >60 y. Ex vivo IFN-γ T cell ELISPOT responses were seen in 10 of 66 (15.1%), whereas only a few expressed CD107a. However, >85% had a high frequency of cultured IFN-γ T cell ELISPOT responses and B cell ELISPOTs. Virus-specific Abs were maintained at ≥16 wk after receiving a single dose of AZD1222, although levels were lower to variants of concern, especially in older individuals. A single dose induced a high frequency of memory T and B cell responses.