But the New Year has brought with it a slow rollout for those currently eligible to receive their coronavirus shots, such as frontline health care workers, their support staff, and nursing home residents. But for those able to get vaccinated, which one of the two vaccines one might receive will largely boil down to where you live, according to public health and life sciences experts.

It’s still too early to tell how things will shake out once production of these vaccines ramps up, but it’s reasonable to assume that bigger cities may have better access to the vaccine that requires colder storage—the vaccine from Pfizer.

While Pfizer’s and Moderna’s respective vaccines stem from the same cool science and have shown similar rates of effectiveness in clinical trials, they have different manufacturing processes, storage requirements, and dosing regimens, meaning that a strong distribution strategy is key.

“It’s much more complex in the United States than in many other countries,” says Ali Tinazli, the chief commercial officer at Fluxergy, a California-based diagnostics specialist that is developing a rapid response COVID testing system.

Tinazli believes that any strategy of distributing the Pfizer and Moderna COVID vaccines—and other potential vaccines that will receive authorization in the future such as AstraZeneca’s and Johnson & Johnson’s—in this country will require a layered approach, whereas in smaller nations there may be deals for one specific vaccine or another to suit their needs.

The U.S. strategy will almost certainly evolve as states and locales identify various bottlenecks and figure out their individual needs for doses. Pfizer’s vaccine, which requires ultracool storage, might be routed to large health systems with more sophisticated abilities such as the Mayo Clinic.

Moderna’s, which comes with more conventional cooling requirements, may be easier to dole out to rural areas, according to health experts. So location will almost certainly dictate which one you receive.

Last week, Moderna announced that it would boost its 2021 production quota for its COVID shot by 20% to 600 million doses, which would reach 300 million people globally since the product, like Pfizer’s, requires two doses. The U.S. is expected to have access to 200 million of those doses by June, according to the company.

As of Jan. 11, just 25.4 million doses, including both of the vaccines currently being used, had been distributed, and only about 9 million people had actually received the first dose of a vaccine in the U.S.

The Centers for Disease Control and Prevention (CDC) issued updated guidance on the issue on distribution strategies on Jan. 7. A key element of the program is decidedly low-tech: a vaccination card or printout that tells you which vaccine you received and the date and location of the shot’s administration, alongside an electronic record copy. That would help prevent mixups between the Pfizer and Moderna vaccines.

But at the end of the day, which one you receive will boil down to your zip code, local health care infrastructure, and the total number of available doses.