Pfizer's experimental COVID-19 vaccine is more than 90 percent effective based on initial trial results, the drugmaker said on Monday, a major victory in the war against a virus that has killed over a million people.

Scientists, public health officials and investors welcomed the first successful interim data from a large-scale clinical test. However, mass roll-outs, which need regulatory approval, will not happen this year.

Pfizer and German partner BioNTech said they had found no serious safety concerns yet and expected to seek the U.S. emergency use authorization (EUA) this month, raising the chance of a regulatory decision as soon as December.

If granted, the companies estimate they can roll out up to 50 million doses this year, enough to protect 25 million people, and then produce up to 1.3 billion doses in 2021.

Experts said they wanted to see the full trial data, but the preliminary results looked encouraging.

"This news made me smile from ear to ear. It is a relief to see such positive results on this vaccine and it bodes well for COVID-19 vaccines in general," said Peter Horby, professor of emerging infectious diseases at the University of Oxford.

Things have to be fixed

There are still many questions, such as how effective the vaccine is by ethnicity or age, and how long it will provide immunity, with social distancing and face covering set to remain for the foreseeable future.

Besides, the vaccine's complex and super-cold storage requirements are an obstacle for even the most sophisticated hospitals in the United States. These may impact when and where it will be available in rural areas or poor countries where resources are tight.

"The cold chain is going to be one of the most challenging aspects of delivery of this vaccination," said Amesh Adalja, senior scholar at Johns Hopkins Center for Health Security.

"This will be a challenge in all settings because hospitals even in big cities do not have storage facilities for a vaccine at that ultra-low temperature."

One of the most prestigious U.S. hospitals, the Mayo Clinic in Rochester, Minnesota, said it does not currently have that capability.

"We're talking about a vaccine that needs storage at minus 70 or 80. That's a tremendous logistical issue not only in the U.S. but outside the Western world," said Dr Gregory Poland, a virologist and vaccine researcher with the Mayo Clinic.

Pfizer expects to seek the U.S. emergency use authorization for people aged 16 to 85. To do so, it will need two months of follow-up safety data to assure no side effects crop up. That is expected to be available in the third week of November.

U.S. Health and Human Services Secretary Alex Azar said it would take several weeks for the U.S. regulators to receive and process the data before a potential approval.

Anthony Fauci, director of the U.S. National Institute of Allergy and Infectious Diseases, greeted Pfizer's breakthrough on Monday, saying the U.S. could have vaccine doses ready to administer to people before the end of the year.

In an interview with CNN, Fauci said he believes he will stay in his current role for the time being and has no intention of leaving.

(With input from Reuters)