The drugmaker Moderna announced on Monday that its coronavirus vaccine is 94.5 percent effective, joining Pfizer as a front-runner vaccine. Moderna has developed the vaccine with the US National Institutes of Health and has come out with promising results in its Phase 3 vaccine efficacy trial. The announcement comes days after Pfizer had released trial results showing 90 percent effectiveness in its vaccine.

Both the vaccines use mRNA or messenger RNA platforms that carry information between different parts of a cell and provide instructions for protein synthesis. The vaccines introduce mRNA that is encoded with a coronavirus-specific antigen into people which leverages the person’s protein synthesis machinery to produce antigens that trigger an immune response.

Moderna’s mRNA delivery platform is very immunogenic. The DSMB (Data and Safety Monitoring Board), an independent group of experts who oversee and monitor patient safety and vaccine efficacy during clinical trials, reported that Moderna trials were safe, the vaccines are well-tolerated by volunteers. Whereas Pfizer’s vaccine, developed in collaboration with Germany’s BioNTech-Fosun Pharma, reported more than 90 percent efficacy in its preliminary analysis with no side effects found.

The vaccines are neck in neck in terms of efficacy percentages, but Pfizer has a big shortcoming in its shelf life and distribution constraints. The Pfizer vaccine will need to be optimally stored at minus 70 degrees Celsius and will degrade in around five days at normal refrigeration temperatures of slightly above freezing.

Two doses of the Pfizer vaccine are required 3 weeks apart to achieve high effectiveness which could make distribution even more complicated.

In contrast, Moderna claims its vaccine can be maintained at most home or medical freezer temperatures for up to six months. Moderna alleges that the vaccine can remain stable for 30 days after thawing at standard refrigerated conditions, of around 2 to 7 degrees Celsius, within the six-month shelf life.

As of now, Moderna seems like the strongest competitor in the race — its easy storage technology puts it ahead of Pfizer.