Isolating and transporting each particular variant from around the world is too much of a hassle. Instead, Pfizer scientists grow the variants themselves, using information from a database called GISAID, which contains virus sequencing data uploaded by scientists and physicians worldwide. The genetic sequence acts as an instruction manual. Swanson’s team downloads the sequences attributed to a particular variant, and runs an algorithm to identify the key mutations. Next, they synthesize the new spike protein, which is what SARS-CoV-2 uses to latch onto and enter human cells.

Most other research centers insert the spike protein into a different, non-pathogenic virus, creating what’s called a pseudovirus, which requires a lower lab security level, but is also less accurate. And so Pfizer’s scientists use another method: The company has samples of the virus from the first Covid-19 case in the U.S., back in January 2020. To create a new variant, its scientists insert the new spike protein into the old SARS-2 virus.

“Our system is very different from a lot of other labs, and I think we’re the only one in the world doing it this way,” said Pei-Yong Shi, a molecular biology professor at the University of Texas Medical Branch who’s working closely with Pfizer to study the variants.