Research in Sri Lanka finds Covishield single dose effectiveness dropped at 16 weeks

Research conducted in Sri Lanka has found that the effectiveness of a single dose of the Oxford–AstraZeneca Covishield vaccine dropped at 16 weeks for those above the age of 60.

Virus specific antibodies were maintained at 16 weeks after receiving a single dose of Oxford–AstraZeneca code-named AZD1222, although levels were lower to variants of concern (VOCs), especially in older individuals.

“Our preprint on waning immunity at 16 weeks after a single dose, in the elderly individuals. Neutralising antibodies and antibodies for variants wane in the elderly but memory responses intact. However, even after a single dose, those younger than 60 had very good responses. 93% had antibodies at 16 weeks, after a single dose,” Professor Neelika Malavige of the Department of Immunology and Molecular Sciences of the Sri Jayawardenepura University tweeted.

A single dose induced a high frequency of memory T and B cell responses, researchers said.

Due to limited access to vaccines, many countries have only administered a single dose of the AZD1222, while the dosage intervals have increased.

Researchers sought to investigate the immunogenicity of a single dose of vaccine at 16 weeks.

SARS-CoV-2 specific antibodies in 553 individuals and antibodies to the receptor binding domain (RBD) of the Wuhan virus (WT) and the variants of concern (VOCs), ACE2 receptor blocking antibodies, ex vivo and cultured IFNγ T cell responses and B cell ELISpot responses were investigated in a sub-cohort.

Results found that the seropositivity rates in those >70 years of age (93.7%) was not significantly different compared to other age groups (97.7 to 98.2, Pearson Chi-Square = 7.8, p-value = 0.05).

The antibody titres (antibody index) significantly declined (p<0.0001) with increase in age. 18/69 (26.1%) of individuals did not have ACE2 receptor blocking antibodies, while responses to the RBD of WT (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 years.

Ex vivo IFN γ T cell ELISpot responses were seen in 10/66 (15.1%), while only a few expressed CD107a.

However, 85% had a high frequency of cultured IFNγ T cell ELISpot responses and B cell ELISpots.

“The seropositivity rates in those >70 years of age (93.7%) was not significantly different compared to other age groups. However, the antibody titres (antibody index) significantly declined (p<0.0001) with increase in age, 16 weeks post-vaccination with a single dose,” Professor in the Department of Family Medicine, University of Sri Jayewardenepura, Dr. Chandima Jeewandara tweeted.

The research paper was prepared by Chandima Jeewandara, Dinuka Guruge, Pradeep Pushpakumara, Achala Kamaladasa, Inoka Aberathna, Shyrar Tanussiya, Banuri Gunasekera, Ayesha Wijesinghe, Osanda Dissanayaka, Heshan Kuruppu, Thushali Ranasinghe, Deshni Jayathilaka, Shashika Dayaratne, Dinithi Ekanayaka, MPDJ Jayamali, Nayanathara Gamalath, Anushika Mudunkotuwa, Gayasha Somathilaka, Madushika Dissanayaka, Michael Harvie, Thashmi Nimasha, Deshan Madushanka, Tibutius Jayadas, Ruwan Wijayamuni, Lisa Schimanski, Pramila Rijal, Tiong Tan, View ORCID ProfileAlain Townsend, Graham Ogg and Gathsaurie Neelika Malavige. (Colombo Gazette)

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