system
Given the following post, respond as if you're commenting on Reddit:
human
What's the difference between the Moderna and Pfizer Covid vaccines?

They seem to be very similar in how they were created, yet one needs a much lower storage temperature and the other has a 4 week gap between doses instead of 3 weeks. What gives?
gpt
RNA is very thermostable at -80C, and becomes increasingly less stable and more prone to degradation as temperatures rise. -20C is a good temperature for storage measured in months, and 4C is good in terms of a few weeks, while room temperature storeage can result in degradation in hours to a few days.

What makes RNA so unstable is the hydroxyl ion at the 2' position of the ribose backbone. This hydroxyl ion can cause hydrolysis of the phosphate linker that connects successive RNA bases in the chain. The higher the temperature, the more likely this is to occur. The hydroxyl is susceptible to other types of degradation, including RNAse enzymes.

 The hydroxyl is missing in DNA (this is what deoxy refers to in DNA) and as a result, DNA is very stable at room temperature, and can strongly resist degradation.

Another important factor is that RNA has structure where lengths of the RNA chain pair up forming "hairpins" and loops. The hydroxyl helps to stabilize these structures that are important for RNA function, and in this conformation, the hydroxyl is also protected, but heat can cause these structures to "melt" and expose the hydroxyl.

Now, an example of a protective modification is the replacement of the 2' hydroxyl with 2'OMe, that is the addition of a methyl group to the oxygen.  RNA used in drug therapies will often have this 2'OMe modification either the entire length of the RNA molecule, or at select positions. There are a number of other modifications that offer some extra  stability to the RNA, as well. And as it happens, Moderna owns the patent to a large number of mRNA modifications. Not only do they own the patents, but they also have an incredible knowledge base and a lot of experience to be to able implement these technologies

Fortunately, in regards to COVID-19, Moderna is not enforcing their patents against other companies that want to use those technologies for their own SARS Cov-2 mRNA vaccines, but it is reasonable that Moderna's vaccine may have greater thermal stability than vaccines made by other companies and they will also be able to more quickly assess the storeage needs for their mRNA than other companies.