PARIS (AFP) - A Covid-19 vaccine that provokes an immune response through white blood cells has shown promise in trials, according to research on Tuesday (Nov 23) that provides new hope for people with compromised immune systems.

The jab, known as CoVac-1 and developed by a team at Germany's University of Tuebingen, was shown to produce a strong white blood cell - or T-cell - response in all 36 phase one trial participants.

T-cells are white blood cells that attack and neutralise whole infected cells. This is unlike an antibody response, provoked by traditional Covid-19 and other vaccines, which targets specific pathogens within the body directly.

This secondary immune response is potentially vital for patients with suppressed immune systems for whom existing Covid-19 vaccines on the market offer weaker levels of protection against severe disease.

Transplant recipients, for example, receive treatment to stifle antibody activity to prevent their bodies from rejecting the life-saving organ.

For them and others, such as cancer patients, bypassing the antibody response and targeting T-cells may prove the best way to mount an immune response to Covid-19. Participants in the trial were aged between 18 and 80 years, and received a single dose of the vaccine.

"CoVac-1 showed a favourable safety profile and induced broad, potent... T-cell responses," the study said, noting that the results were the same when tested against Covid-19 variants.

The team reported that the strength of the T-cell response provoked by the jab was stronger than what had been observed through infection with Covid-19.

The effects of the jab were seen to last up to three months, according to the research, which was published in the prestigious Nature journal.

The report said the very preliminary results support the already ongoing phase two trials being conducted in patients with immunodeficiencies.

Phase two trials typically contain larger cohorts and will likely provide important data on the vaccine's efficacy and safety for all types of patients.

"CoVac-1 may well serve as a (complementary) vaccine... particularly in elderly and immunocompromised individuals with impaired ability to mount sufficient immune responses after Sars-CoV-2 vaccination with currently approved vaccines," it added, referring to the virus that causes Covid-19.