The University of Oxford’s vaccine candidate showed promising signs when tested in a small number of monkeys, according to a new study.

Six rhesus macaques were given half the dose of the vaccine currently being tested in humans.

The paper, which also looked at mice, showed some of the animals developed antibodies to the virus within 14 days of being vaccinated, with all of them displaying evidence of antibodies within 28 days.

According to the study, which has not been peer-reviewed, a single vaccination dose was also effective in preventing damage to the lungs – organs that can be severely affected by the virus.

The authors wrote: “We observed a significantly reduced viral load in bronchoalveolar lavage fluid and respiratory tract tissue of vaccinated animals challenged with SARS-CoV-2 compared with control animals, and no pneumonia was observed in vaccinated rhesus macaques.

“Importantly, no evidence of immune-enhanced disease following viral challenge in vaccinated animals was observed.”

The researchers further found viral loads in the lower respiratory system were significantly reduced, suggesting vaccination prevents virus replication in the lower respiratory tract.

Despite this marked difference in virus replication in the lungs, reduction in viral shedding from the nose was not observed.

Stephen Evans, professor of pharmacoepidemiology at the London School of Hygiene and Tropical Medicine, said the results were “very definitely” good news, adding: “The most important finding to me is the combination of considerable efficacy in terms of viral load and subsequent pneumonia, but no evidence of immune-enhanced disease.

“The latter has been a concern for vaccines in general, for example with vaccines against respiratory syncytial virus (RSV), and for SARS vaccines.

“This was a definite theoretical concern for a vaccine against SARS Cov-2 and finding no evidence for it in this study is very encouraging.”

He added that it was not known whether the trials in the macaques would translate into humans.

Dr Penny Ward, visiting professor in pharmaceutical medicine at King’s College London and chairwoman of the education and standards committee of the Faculty of Pharmaceutical Medicine, said: “This publication describes two preclinical studies which investigated immune response to vaccination with the Jenner Institute SARS Cov2 vaccine in murine and primate models.

“Single doses of the vaccine produced high quantities of neutralising antibody in both species.

“One concern with vaccines against CoV species is the potential for antibody dependent enhancement of the disease pathology – this is one reason for the lack of a vaccine against the 2003 SARS CoV strain.

“It is helpful to see that monkeys vaccinated with this SARS CoV2 vaccine did not have any evidence of enhanced lung pathology and that, despite some evidence of upper respiratory tract infection by SARS COV2 after high viral load virus challenge, monkeys given the vaccine did not have any evidence of pneumonia.

“These results support the ongoing clinical trial of the vaccine in humans, the results of which are eagerly awaited.”