AstraZeneca and Oxford University's potential Covid-19 vaccine produced a strong immune response in older adults, data published yesterday showed as the world Health Organisation warned that vaccines would not arrive in time to defeat the second wave of the pandemic. 

The data, reported in part last month but published in full in The Lancet medical journal yesterday, suggest that those aged over 70, who are at higher risk of serious illness and death from Covid-19, could build robust immunity.

"The robust antibody and T-cell responses seen in older people in our study are encouraging," said Maheshi Ramasamy, a consultant and co-lead investigator at the Oxford Vaccine Group.

"We hope that this means our vaccine will help to protect some of the most vulnerable people in society, but further research will be needed before we can be sure."

Late-stage, or Phase III, trials are ongoing to confirm the findings, researchers said, and to test whether the vaccine protects against infection with SARS-CoV-2 in a broad range of people, including people with underlying health conditions.

Results of those trials should definitely be known by Christmas, the Oxford Vaccine Group's director, Andrew Pollard, said, adding it was too early to know whether and how well the vaccine works in preventing Covid-19 disease.

"We're still waiting to get to the point where we can do the analysis to just work out how well the vaccine can protect people, and we're getting ever closer to that," he told journalists.

The Oxford-AstraZeneca Covid-19 vaccine candidate, called AZD1222 or ChAdOx1 nCoV-19, had been among the front-runners in global efforts to develop shots to protect against infection with the novel coronavirus, or SARS-CoV-2.

Pfizer said Wednesday that a completed study of its experimental vaccine showed it was 95 percent effective, while fellow US firm Moderna said this week that its own candidate was 94.5 percent effective. Russia claims its candidate is more than 90 percent effective.

"We're not in a rush. It's not a competition with the other developers," Oxford's Pollard said, adding that AstraZeneca would release headline efficacy data before it was published in an academic journal.

Unlike the Pfizer-BioNTech and Moderna shots, both of which use new technology known as messenger RNA (mRNA), AstraZeneca's is a viral vector vaccine made from a weakened version of a common cold virus found in chimpanzees.

The Phase II trial reported in The Lancet involved a total of 560 healthy volunteers, with 160 aged 18-55, 160 aged 56-69, and 240 aged 70 or over.

Volunteers got two doses of the vaccine or a placebo, and no serious side effects related to the AZD1222 vaccine were reported, the researchers said.

AstraZeneca has signed several supply and manufacturing deals with companies and governments around the world.

Meanwhile, while acknowledging the vaccine news as encouraging, WHO urged world not to be too hopeful, at least not for the ongoing second wave of pandemic.

The WHO's Michael Ryan said vaccines should not be seen as a "unicorn" magic solution -- and countries battling a resurgence of the virus would once again have to "climb this mountain" without them.

"I think it's at least four to six months before we have significant levels of vaccination going on anywhere," he said, during a public question and answer session live on social media.

Despite recent promising announcements from final-phase candidate vaccine trials, "We're not there with vaccines yet," said Ryan.

"Many countries are going through this wave, and they're going to go through this wave, and continue through this wave, without vaccines.

"We need to understand and internalise that, and realise: we have got to climb this mountain this time, without vaccines."

Ryan warned against slackening off individual vigilance against the virus in the mistaken belief that vaccines would now solve the problem instead.

"Some people think a vaccine will be, in a sense, the solution: the unicorn we've all been chasing. It's not," the Irishman said.

"If we add vaccines and forget the other things, Covid does not go to zero."

The number of new Covid-19 cases in Europe declined last week for the first time in over three months, but deaths in the region continued to climb, WHO data showed Wednesday.

While at least 55.6 million cases worldwide have been registered since the outbreak emerged in China last December, the novel coronavirus has killed more than 1.3 million people around the globe, according to a tally from official sources compiled by AFP.