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Moderna's vaccine can last for weeks in a refrigerator, expanding an edge on rivals.

Moderna on Monday claimed its experimental coronavirus vaccine, once thawed, can remain stable for up to 30 days when stored at temperatures between 2 to 8 degrees Celsius, citing new data that significantly improves on the seven-day window the company had previously communicated.

A 30-day shelf life should make the vaccine more useful for mass vaccination programs since it could be kept in refrigerators at pharmacies, doctor's offices, hospitals and public health organizations. A similar vaccine from Pfizer and BioNTech can only be stored at refrigerator temperatures for five days.

Early results from large clinical trials have shown both vaccines to be more than 90% effective at preventing cases of COVID-19, according to their respective developers. Each requires two shots spaced a few weeks apart, however, making storage critical to any immunization plan. For shipping and longer-term storage, Pfizer and BioNTech's vaccine must be kept at minus 70 degrees Celsius, while Moderna's can be held at minus 20 degrees Celsius — the temperature of a home freezer.

The Phase 3 trial results from Moderna and the team of Pfizer and BioNTech suggest the two vaccines are comparably effective. But the smaller biotech company may have an edge when it comes to storing and shipping its shot.

Early stability data had raised questions of whether either vaccine could be stored in a doctor's office, and therefore, how widely they could be used if proven safe and effective. Both rely on messenger RNA to stimulate an immune response, a newer drug-making technology that hasn't yet resulted in an approved drug.

While messenger RNA has now proven uniquely suited to quickly developing vaccine candidates, there are drawbacks as well. RNA molecules are chemically unstable and sensitive to temperature as well as to enzymes that can break them down. That sensitivity makes storage, transportation and distribution a key challenge for manufacturers to overcome.

Pfizer and BioNTech's ultra-cold storage requirements, for example, forced the partner comapnies to develop a special shipping box.

As recently as an August meeting of a Centers for Disease Control and Prevention advisory committee, Pfizer and BIoNTech's vaccine was believed to be refrigerator-stable for 24 hours. At that time, those characteristics were viewed as limiting the shot's use to "centralized sites with adequate equipment and high throughput," such as healthcare facilities.

BioNTech now says, however, the vaccine can be kept at 2 to 8 degrees Celsius for up to five days, which improves its potential utility. And CEO Ugur Sahin told investors last week that there are more stability studies underway to determine whether the vaccine can be stored at minus 20 and minus 40 degrees Celsius, as well as "extended storage" at 2-8 degrees Celsius. The company expects its next update in mid-December.

In the meantime, Moderna's latest announcement should ease concerns that storage and distribution challenges will limit uptake of its shot.

"To have a vaccine that is stable at refrigerator temperatures for up to 30 days is an enormous advantage for mass vaccination programs," Paul Offit, director of the vaccine education center at Children's Hospital of Philadelphia, said in an email.

Moderna plans to seek an emergency clearance from the Food and Drug Administration in the coming weeks after fuller safety data are collected. Pfizer should as well, also pending positive safety results that are expected shortly. Assuming each are approved, the companies estimate they can manufacture a combined 50 million to 60 million doses for use in the U.S. before the end of the year.

Author:Jonathan Gardner


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