The single dose Johnson & Johnson's Covid-19 vaccine has shown strong neutralising antibody activity against the Delta (B16172) variant, with immunity lasting at least eight months, according to results of phase-III trials.

The vaccine is 85 per cent effective against severe/critical disease and demonstrated protection against hospitalisation and death from the deadly coronavirus.

The phase-III trials, submitted preprint to bioRxiv, showed the vaccine was consistently effective across all regions studied globally, including in South Africa and Brazil, where there was a high prevalence of rapidly emerging Beta and Zeta (P2) variants during the study period.

It also generated neutralising antibodies against a range of other SARS-CoV-2 variants of concern, which increased over time, such as the Gamma (P1) variants and the Alpha (B117), Epsilon (B1429), Kappa (B16171) and D614G variants, as well as the original SARS-CoV-2 strain.

"Today's newly announced studies reinforce the ability of the Johnson & Johnson Covid-19 vaccine to help protect the health of people globally," said Paul Stoffels, Vice Chairman of the Executive Committee and Chief Scientific Officer at Johnson & Johnson, in a statement on Thursday.

"We believe that our vaccine offers durable protection against Covid-19 and elicits neutralising activity against the Delta variant. This adds to the robust body of clinical data supporting our single-shot vaccine's ability to protect against multiple variants of concern," he added.

Further, data from a sub-study of the company's Phase 1/2a Covid-19 vaccine study, also submitted preprint to bioRxiv, showed that humoral and cellular immune responses generated by the single-shot Covid-19 vaccine lasted through at least eight months.

T-cell responses, including CD8+ T-cells that seek out and destroy infected cells, persisted over the eight-month timeframe examined.

"Current data for the eight months studied so far show that the single-shot Johnson & Johnson Covid-19 vaccine generates a strong neutralising antibody response that does not wane; rather, we observe an improvement over time. In addition, we observe a persistent and particularly robust, durable cellular immune response," said Mathai Mammen, Global Head, Janssen Research & Development, Johnson & Johnson.

"With each new dataset, we build on our solid foundation of evidence that our single-shot Covid-19 vaccine plays a critical role in ending the pandemic, which continues to evolve and pose new challenges to global health," he added.

The Johnson & Johnson Covid-19 single-dose vaccine is compatible with standard vaccine storage and distribution channels with ease of delivery to remote areas. The vaccine is estimated to remain stable for two years at minus 4 degrees Fahrenheit (minus 20 degrees Celsius), and a maximum of 4.5 months at routine refrigeration temperatures of 36 - 46 degrees Fahrenheit (2-8 degrees Celsius).