Johnson & Johnson (J&J) has reported that interim data from a Phase I/IIa sub-study of its single-dose Covid-19 vaccine showed robust and long-lasting immune responses against the Delta variant (B.1.617.2) and other SARS-CoV-2 variants of concern.

The Phase I/IIa trial is assessing the safety, reactogenicity and immunogenicity of the vaccine at two dose levels given intramuscularly as a single dose, or two doses administered eight weeks apart in healthy adults.

This multi-centre, randomised, double-blind, placebo-controlled trial is progressing at multiple sites in Belgium and the US.

The latest sub-study data are from cohort Ib of the Phase I/IIa trial, which recruited 25 adult subjects aged 18 to 55 years at the Beth Israel Deaconess Medical Center for descriptive exploratory immunogenicity studies.

Interim data showed that the humoral (antibody) and cellular (T-cell) immune responses by the vaccine lasted for eight months after vaccination.

T-cell responses, including CD8+ T-cells that find and destroy infected cells, lasted more than the assessed eight-month timeframe.

The study also indicated maturation of B-cell response without requiring boosting. Mature B-cells generate antibodies to help fight SARS-CoV-2.

Furthermore, results showed that the vaccine also induced dual mechanisms of protection against variants of concern, including the Alpha (B.1.1.7), Beta (B.1.351), Gamma (P.1), Epsilon (B.1.429) and Kappa (B.1.617.1), as well as original strain (WA1/2020).

J&J noted that the data signify an expansion of neutralising antibodies over eight months, together with lasting T-cell responses and the indication of B-cell maturation.

J&J Janssen Research & Development global head Mathai Mammen said: “The study showed that variant-specific neutralising antibodies increased over the eight months examined after vaccination which suggests the maturation of B-cell responses.

“In addition, the T-cell responses are especially strong and stable over time, which is also potentially important for activity against these variants.”

In April 2021, J&J expanded the Phase IIa trial of the Covid-19 vaccine candidate to include adolescent subjects aged 12 to 17 years.