Swiss regulators have said that data submitted by AstraZeneca is not sufficient for them to authorise use of the company's Covid-19 vaccine and "new studies" are needed.
The Swissmedic regulatory authority said it had been examining information from AstraZeneca but that was "not yet sufficient to permit authorisation".
"To obtain more information about safety, efficacy and quality, additional data from new studies are needed," it said in a statement.
Switzerland has so far given the green light to Covid-19 vaccines made by Pfizer-BioNTech and Moderna.
It had been expected to authorise the AstraZeneca jab soon, after the European Union last week gave the vaccine the go ahead.
But while the EU granted approval for use in all people over the age of 18, several European countries have advised against giving the jabs to people over 65, citing lack of evidence that it was effective among the elderly.
Swissmedic said a meeting of its external advisory body today had confirmed its interim assessment of the AstraZeneca vaccine data.
"The data currently available do not point to a positive decision regarding benefits and risks," it said.
"To obtain a conclusive assessment, the applicant will among other things have to submit additional efficacy data from a Phase 3 trial under way in North and South America, and these will have to be analysed.
"As soon as the results have been received, a temporary authorisation according to the rolling procedure could be issued at very short notice," it added.
Oxford/AstraZeneca vaccine cuts virus transmission - study
The Oxford-AstraZeneca vaccine significantly reduces virus transmission and is highly protective after a single dose, according to an Oxford University study, which the UK government said vindicated its inoculation strategy.
"It does show the world that the Oxford jab works, it works well," Health Secretary Matt Hancock told BBC radio, hailing the study's findings as "good news".
"It slows transmission by around two-thirds, so it categorically supports the strategy that we're undertaking," he said.
The Oxford study, which is awaiting peer review, found that those who had been vaccinated with a single dose of the vaccine were 67% less likely to test positive with a PCR test, "suggesting the potential for a substantial reduction in transmission".
It also provided backing for the UK's strategy of administering as many first doses of vaccine to high-risk groups as possible and allowing a 12-week interval before the second dose, which has been criticised by some experts.
The other vaccine already being rolled out in the UK, the Pfizer-BioNTech, was designed to be administered with a shorter interval.
"We are confident that the 12-week dosing schedule is the right one for both of the vaccines that we're using in the UK," Mr Hancock said.
Researchers found that a single dose was 76% effective in preventing virus symptoms after 22 days and for up to 90 days, while it did not prevent asymptomatic illness.
It was more effective to wait 90 days than to administer the second dose, researchers found "providing further support for current policy".
The survey had 17,177 participants in the UK, Brazil and South Africa. The data covers the period up to 7 December 2020. None of those studied were hospitalised.
The vaccine is cheap to produce and is being sold at cost price. It can also be stored at fridge temperature, while the Pfizer vaccine requires extremely cold storage.
The Assistant Professor of Virology at University College Dublin said the AstraZenca data gives everyone even more hope.
Speaking on RTÉ's Today with Claire Byrne, Dr Gerald Barry said previously there was no data to suggest that a vaccine could prevent a person from potentially transmitting the virus if they were infected.
He explained that this is important because anyone who is not vaccinated remains vulnerable and a potential petri dish scenario where the virus could mutate and continue to circulate.
Ideally, Dr Barry said, you want a vaccine that is neutralising and stops both infection and transmission.
He said that there are clear indications that the vaccine is having a positive impact in Israel and hospitalisations and severe disease in older populations are dropping.
When asked about the Russian vaccine, he said that he "thinks it is great" and the data coming out of the Russian studies is very positive.