The United Kingdom has approved another coronavirus vaccine for use, weeks after the country became the first in the world to start inoculating its citizens.

In a statement, the UK government said the Medicines and Healthcare Products Regulatory Agency (MHRA) had authorized Oxford University/AstraZeneca's Covid-19 vaccine following "rigorous clinical trials and a thorough analysis of the data by experts at the MHRA."

The UK is the first country to approve the Oxford University/AstraZeneca vaccine.

The vaccine had met "strict standards of safety, quality and effectiveness," the statement added.

"The NHS has a clear vaccine delivery plan and decades of experience in delivering large scale vaccination programmes. It has already vaccinated hundreds of thousands of patients with the Pfizer/BioNTech vaccine and its roll out will continue. Now the NHS will begin putting their extensive preparations into action to roll out the Oxford University/AstraZeneca vaccine."

Previously, the team developing the vaccine said it had an "an average efficacy of 70%," with one dosing regimen showing an efficacy of 90%.

"Excitingly, we've found that one of our dosing regimens may be around 90% effective and if this dosing regime is used, more people could be vaccinated with planned vaccine supply," Andrew Pollard, chief investigator of the Oxford Vaccine Trial, said in November.

AstraZeneca has promised to supply hundreds of millions of doses to low and middle-income countries, and to deliver the vaccine on a not-for-profit basis to those nations in perpetuity.

The vaccine -- developed at England's Oxford University -- is significantly cheaper than the others and, crucially, it would be far easier to transport and distribute in developing countries than its rivals since it does not need to be stored at freezing temperatures.

"I think it's the only vaccine that can be used in those settings at the current time," Azra Ghani, chair in infectious disease epidemiology at Imperial College London, told CNN.

The Oxford/AstraZeneca vaccine can be kept at refrigerator temperatures of 2 to 8 degrees Celsius (36 to 46 degrees Fahrenheit) for at least six months. Moderna's vaccine has to be stored at minus 20 degrees Celsius (minus 4 degrees Fahrenheit) -- or at refrigerator temperatures for up to 30 days -- and the Pfizer/BioNTech vaccine has to be stored at minus 75 degrees Celsius (minus 103 degrees Fahrenheit), and used within five days once refrigerated at higher temperatures.

"Pfizer and Moderna require freezer storage, and that just isn't in place in many settings," Ghani said.

"Cold chain" refrigeration is the standard storage used globally to deliver vaccines from central locations to local health clinics. AstraZeneca's vaccine is so far "the only one that can definitely be delivered to those systems," added Ghani.

The vaccines are based on different technology. AstraZeneca's offering -- like Johnson & Johnson's vaccine and Russia's Sputnik V -- uses an adenovirus to carry genetic fragments of coronavirus into the body.