There has been a cautiously optimistic reaction from medical experts after Pfizer said its experimental vaccine was more than 90% effective in preventing Covid-19 based on initial data from a large study.

The development marks a major victory in the fight against the pandemic.

Pfizer and German partner BioNTech SE are the first drug-makers to show successful data from a large-scale clinical trial of a coronavirus vaccine.

Medical, scientific and business figures have all been reacting to the news

John Moore, Professor at Weill Cornell Medical College, New York City

"I can see nothing problematic."

As for what this means for other vaccines, Prof Moore said:"Moderna's is likely to work as well given the similar design and performance, and Novavax also, as it seems more potent. It's harder to judge about the other candidates."

Lawrence Young, Professor of Molecular Oncology at University of Warwick, Britain

"It's hard to interpret the interim analysis, but it does appear very encouraging."

"In this... preliminary analysis there is a significant reduction in the Covid-19, and I interpret that to mean that ...individuals are not developing disease, but it doesn't tell us anything about whether people are getting infected or not."

Michael Head, Senior Research Fellow in Global Health, University of Southampton

"This cautiously sounds like an excellent result from the phase 3 trials, but we should remain a little cautious.  Theprovisional findings are made available in a press release, and the study is ongoing. However, if the final results show an effectiveness of anywhere near 90% with response in elderly and ethnic minority populations, that is an excellent result for a first generation vaccine.

"This has been seen before - the rapidly-produced ebola vaccine generated very high levels of effectiveness and exceeded all expectations.

"Equally, billions of dollars and numerous clinical trials have struggled to produce any form of vaccination against HIV. Science can be unpredictable."

Azra Ghani, Chair In Infectious Disease Epidemiology, Imperial College London

"These new results represent the first demonstration of substantial efficacy of a vaccine candidate against Covid-19 disease which is very welcome news.  It is important to bear in mind that these are early results based on a relatively small number of cases.  

"In addition, the efficacy estimate is based on seven days of follow-up of participants following the second dose; further data in the coming weeks and months will provide a better picture of longer-term vaccine efficacy."

William Schaffner, Infectious Diseases Expert at Vanderbilt University Medical Center, Nashville, Tennessee, United States.

"The efficacy data are really impressive. This is better than most of us anticipated. I would have been delighted with efficacy of 70% or 75%. 90% is very impressive for any vaccine. The study isn't completed yet, but nonetheless the data look very solid."

Ian Jones, Professor of Virology at University of Reading, Britain

"Of all the vaccines currently in development the BioNtech product always looked like the most bang-per-buck as it is entirely focused on the part of the virus that binds to the human cell, the receptor binding domain.

"The only things we will not know for some time is the longevity of the response in all age groups, but assuming antibody titres are high that should be at least as good as any other vaccine currently in trial."

Florian Krammer, Professor at the Department of Microbiology, Icahn School of Medicine at Mount Sinai, USA

"These are fantastic results. The efficacy could be higher than expected, and this probably means that - at least in the US - there will be an application for approval very soon. Of course, it would be better to see age-specific data, but I suspect that these will be published soon. Frankly, this is the best news I have received since 10 January.."

Marylyn Addo, Head of Tropical Medicine Section, University Medical Center Eppendorf, Hamburg, Germany

"These are interesting first signals, but again they are only communicated in press releases. Primary data are not yet available and a peer-reviewed publication is still pending. We still have to wait for the exact data before we can make a final assessment. At present, there are still few details about the exact data, for example regarding different age groups and in which groups the 94 cases occurred exactly."

Bernd Salzberger, Head of Infectiology, University Hospital Regensburg, Germany

"In the Pfizer/Biontech press release, the Phase II/III placebo-controlled observer-blinded study with the vaccine BNT162b2 reported a vaccine efficacy of over 90%. Although only a few events - a total of 94 cases - have been observed in the study so far, this is a very good result. No serious side effects have been reported - overall a very positive result, which will probably lead to an early approval."

Gerd Faetkenheuer, Head Of Infectiology, Clinic I for Internal Medicine, University Hospital Cologne, Germany

"These are great and promising data. It is incredible that in such a short period of time this progress with the development of a vaccine and clinical trials within a few months has been achieved. The results on efficacy and safety so far are excellent.

"I think this will have a major impact on our handling of the pandemic and I hope that large quantities of the vaccine will be available quickly. The researchers involved can only be congratulated".

Danny Altmann, Professor of Immunology at Imperial College London

In terms of the impact on the Covid-19 pandemic, "it's good news, but it's not 'overnight success' good news".

Prof Altmann cautioned that this and other potentially successful vaccines would still need to be approved and delivered to people across the world, and this will still take many months.

He added, however: "I always felt optimistic, and my optimism remains strong."