(Reuters) -GlaxoSmithKline and CureVac said a study here on macaque monkeys showed their jointly-developed mRNA COVID-19 vaccine candidate to be "strongly improved" in protecting against the virus compared with CureVac"s first attempt. The encouraging news on its “second-generation” vaccine gave CureVac’s German-listed shares an 8% lift, as the stock gradually recovers from a slump in June when the German biotech company’s first vaccine candidate recorded a disappointing 48% efficacy in mass testing on humans. The companies said on Monday that a blood analysis of the animals showed that the next-generation vaccine known as CV2CoV triggered virus-fighting antibodies as well as immune cells that target infected cells faster and in greater quantities than CureVac’s first-generation vaccine candidate. The surge in antibodies and immune cells was similar to that observed after a real infection with SARS-CoV-2, the coronavirus that causes COVID-19, they said. Higher antibody blood counts were observed across virus variants of concern, including the Beta, Delta and Lambda lineages, they added. When infected with the original SARS-CoV-2 virus detected in the Chinese city of Wuhan, macaques vaccinated with CV2CoV had better clearance of the virus in the lungs and nasal passages, when comparing the two vaccines. The results have yet to be peer-reviewed for publication in a medical journal. U.S.-listed shares of CureVac, which also reported its quarterly financial results on Monday, were up 9.5% in pre-market trading. GSK and CureVac teamed up in February in a 150 million euro ($177 million) deal to develop the next-generation COVID-19 vaccine from next year, in an attempt to tackle several variants with one shot. Initial testing of CV2CoV on humans would begin during the last quarter of this year, CureVac said. ($1 = 0.8496 euros) Reporting by Yadarisa Shabong in Bengaluru; Editing by Maju Samuel and Barbara Lewis Our Standards: The Thomson Reuters Trust Principles.