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July 2 (Reuters) - Johnson & Johnson said late Thursday that its single-shot COVID-19 vaccine showed promise against the highly contagious Delta variant in a laboratory study.

An analysis of blood from eight patients showed that immune responses elicited by the vaccine against the Delta variant, first identified in India, were at a higher level than against the Beta variant, which was first identified in South Africa.

The World Health Organization has said Delta is becoming the globally dominant variant of COVID-19, raising concerns over whether existing vaccines will work against it.

So far, preliminary data has shown that vaccines made by Pfizer Inc and BioNTech, AstraZeneca and Moderna are largely protective against Delta, with the concentration of virus-neutralizing antibodies being somewhat reduced.

"We believe that our vaccine offers durable protection against COVID-19 and elicits neutralizing activity against the Delta variant," Johnson & Johnson Chief Scientific Officer Paul Stoffels said.

Disease experts believe the J&J's vaccine may require booster shots of the Pfizer/BioNTech or Moderna vaccines to be more effective against the Delta variant.

U.S. public health officials have said there is no clinical data to support the move.

"The data should take center stage as the more-virulent Delta variant drives a global surge in COVID-19 infections and gains ground in the United States," Cantor Fitzgerald analyst Louise Chen said.

J&J has submitted the data as a preprint to the website bioRxiv, a free online archive of unpublished clinical studies, ahead of peer review.

Data from a separate study also showed that immune response for recipients of the vaccine lasted at least eight months.

"The single-shot Johnson & Johnson COVID-19 vaccine generates a strong neutralizing antibody response that does not wane; rather, we observe an improvement over time," Mathai Mammen, head of research and development at J&J's drugs business, said.

(Reporting by Aakriti Bhalla and Manas Mishra in Bengaluru; Editing by Sherry Jacob-Phillips and Arun Koyyur)