By the end of this week, people in the country worst-hit by COVID-19 could gain access to a second COVID-19 vaccine. On Tuesday (Dec 15), the US Food and Drug Administration (FDA) endorsed mRNA-1273 - the vaccine candidate made by American biotechnology company Moderna - as safe and effective.
This paves the way for the vaccine's emergency authorisation, a decision that the FDA will make after a panel of outside advisers meets on Thursday.
Singapore has also approved the Pfizer-BioNTech vaccine, with the first shipment expected by the end of the year.
Other countries such as Canada, Saudi Arabia, Mexico and Kuwait have also authorised the use of the Pfizer-BioNTech vaccine. A big group that could soon follow, if the European Union gives its final approval, which could come as early as Dec 23.
A third COVID-19 vaccine, developed by China's Sinovac Biotech, is also currently in late-stage trials. Indonesia already has 1.2 million doses of CoronaVac, the vaccine it has been testing since August.
Here’s a look at how the three COVID-19 vaccines differ:
The COVID-19 vaccine developed by US pharmaceutical giant Pfizer and Germany’s BioNTech was the first COVID-19 vaccine to be approved by the US FDA for emergency use.
How it works: The Pfizer-BioNTech vaccine uses messenger RNA (mRNA) technology. mRNA vaccines teach our cells to make a protein that triggers an immune response inside our bodies. This is different from traditional vaccines which put a weakened or inactivated germ into our bodies.
Storage: Pfizer-BioNTech's COVID-19 vaccines need to be kept at minus 70 degrees Celsius, which presents logistical challenges, especially for poorer countries.
Efficacy: 95 per cent
Rollout: Britain was the first country in the world to roll out injections on Dec 8, with the US following around a week later on Dec 16. Singapore, Canada, Mexico and Saudi Arabia have also authorised the use of the Pfizer-BioNTech COVID-19 vaccine.
The initial results from Moderna's vaccine were described a month ago by the US' leading expert on infectious diseases Anthony Fauci as "stunningly impressive".
How it works: Just like the Pfizer-BioNTech vaccine, the Moderna vaccine uses mRNA technology.
Storage: Can be kept for 30 days with refrigeration, six months at minus 20 degrees Celsius.
Efficacy: 94.5 per cent
Rollout: None as of Dec 16.
Developed by China's Sinovac Biotech, the vaccine, known as CoronaVac, is currently undergoing phase 3 clinical trials in places such as Brazil and Indonesia.
How it works: Sinovac's vaccine uses inactivated vaccine technology, which utilises virus particles that have been killed to stimulate our bodies to produce an immune response. This vaccine is similar to the flu vaccine.
Storage: The vaccine can be stored at normal fridge temperatures of 2 to 8 degrees Celsius and may remain stable for up to three years. This may be an attractive option for places where access to refrigeration is challenging.
Rollout: None as of Dec 16.
Editor's note: An earlier version of this story stated that the chickenpox and MMR vaccines are inactivated vaccines. They are not. We are sorry for the error.