The most exciting thing about Pfizer’s Covid-19 vaccine isn’t that it works

Pfizer and BioNTech’s announcement of preliminary efficacy results for their Covid-19 vaccine candidate is a tiny speck of light at the end of a long, dark tunnel. Based on interim data from a late stage clinical trial, their candidate could prevent 90% of Covid-19 infections.

There are still questions about how effective the vaccine would be in the real world, but there’s one thing scientists know for sure: This vaccine model could massively accelerate the process of making vaccines for future pandemics.

Pfizer and BioNTech’s vaccine candidate isn’t a live virus that’s been weakened, or a killed virus. Even though historically, these vaccine platforms have produced the strongest antibody responses (pdf), they can take years and sometimes over a decade to develop—not ideal for squashing a quickly-spreading pandemic.

Instead, it’s what’s called an mRNA vaccine. If the US Food and Drug Administration (FDA) grants it emergency use authorization or eventual approval, it’d be the first of its kind on the market. This class of mRNA vaccines could make vaccines against new pathogens available shortly after scientists sequence its genetic material, says Malcolm Duthie, a professor in the department of global health at the University of Washington. “It speeds it up at the pandemic response immensely,” he says.

One bottleneck in traditional vaccine development is figuring out how to safely mimic an external pathogen. This means building a properly folded protein facade or genetically altering a virus so that cells register it as a threat without being under threat. With mRNA vaccines, researchers can skip that step; instead, they give cells the instructions for mounting defenses against a virus that isn’t there.

Pfizer and BioNTech’s mRNA vaccine provides the cellular ingredient list not for a virus, but for the antibodies that target the signature spike protein on SARS-CoV-2. When our cells make the proteins they need to survive, mRNA—short for messenger RNA—is the intermediary genetic material translated from DNA, akin to the shopping list you write yourself after reading a recipe in a cookbook.

To get that mRNA into your cells, the vaccine designers put it in a fatty envelope that has the same chemical characteristics as certain proteins that can shimmy their way through our cell membranes. Once inside, the fatty envelope degrades, and little protein factories called ribosomes read the mRNA inside to start making select snippets of the SARS-CoV-2 virus, which kicks of antibody production.

The fact that Pfizer and BioNTech’s vaccine seems to have worked so well means that they were right that the signature spike protein on the SARS-CoV-2 virus was a good target. But it also means that—for the very first time—mRNA vaccines seem to have worked. If they do, researchers working to develop vaccines for future pandemics will have a blueprint of how to quickly develop vaccines against them.

BioNTech, which initially developed the candidate, had come up with dozens of targets just a few weeks after the virus was genetically sequenced back in January; by May, it had narrowed them down to four candidates for early safety testing in humans, and by July, it had homed in on the candidate that would eventually be scaled up in the large clinical trials conducted with Pfizer. That kind of timeline is unheard of in the study of vaccines.

Pfizer and BioNTech aren’t the ones group working on an mRNA vaccine; Moderna is also working on an mRNA Covid-19 vaccine candidate, which had a similarly speedy development timeline. Moderna is also in late-stage clinical trials, and is expected to be able to start parsing through its data in just a few weeks.

The one downside of the positive results for this new vaccine design: new storage and distribution plans. Pfizer and Moderna have stated that their vaccines need to be kept at -70°C and -20°C respectively, which is significantly colder than most vaccines. Without these extremely cold temperatures, Duthie says, the mRNA and lipid nanoparticles can lose their integrity. But if mRNA vaccines become standard, the world will be prepared with plenty of deep freezers for their next deployment.