Early data showing Pfizer's coronavirus vaccine candidate is more than 90% effective turned a lot of heads this week, but experts say the drugmaker faces a number of obstacles in getting its vaccine to the public.

The first hurdle: FDA authorization and manufacturing

Pfizer has said it intends to seek an emergency use authorization from FDA within the next week, once it has a total of two months of safety data. That puts the vaccine on track to be authorized by FDA as early as December, the Wall Street Journal reports.

Once the vaccine is authorized, Pfizer will need to produce massive quantities of the drug. Albert Bourla, Pfizer's CEO, said that, by the end of the year, the company will have enough doses for 25 million people.

In 2021, Pfizer said it will produce enough of the vaccine for 630 million people and will continue to increase production later in the year with a goal of producing 1.3 billion doses total. Bourla said that some priority groups, such as first responders, would potentially be able to walk into a pharmacy and receive the vaccine by the middle of 2021.

Even so, it will take time before enough of the population receives the vaccine that herd immunity is reached, experts say. Roy Anderson, an epidemiologist and professor at Imperial College London, said that assuming the vaccine maintains its 90% effectiveness, at least 75% of the population will need to receive the shot to reach herd immunity.

"We're realistically talking about the middle of next year before there is any significant uptake," Martin McKee, professor of European public health at the London School of Hygiene and Tropical Medicine, said.

The second hurdle: Distribution

If the Pfizer gets FDA's OK for the drug and meets its own manufacturing goals, the drugmaker will then need to ensure it can be distributed—and the company has already thought through major aspects of this process.

The vaccine will be manufactured in Kalamazoo, Michigan, before it's shipped out to the rest of the United States.

For shipment and storage, the company has created thermal containers to safely transport the vaccines, which must be stored at a temperature of 94 degrees below zero Fahrenheit, NBC News reports. The vaccines will be packaged beneath dry ice and will be shipped via air to large distribution hubs nationwide. From there, the vaccines will be sent via ground transport to dosing locations, which could include "hospitals, outpatient clinics, community vaccination locations, and pharmacies," according to Kim Bencker, a spokesperson for Pfizer.

Each shipment of the vaccine will have a GPS-tracked thermal sensor to monitor both the temperature and location of the vaccine, which Pfizer said will "proactively" prevent "deviations," such as accidents or theft.

After the vaccine is delivered, the company has said doses can be stored for up to six months in ultra-low temperature freezers, up to five days in a refrigeration unit, or up to 15 days in their original packaging with new dry ice, NBC News reports.

Experts say the logistics of transporting and storing the vaccine at such low temperatures will present a significant challenge.

"The cold chain is going to be one of the most challenging aspects of delivery of this vaccination," Amesh Adalja, senior scholar at Johns Hopkins Center for Health Security, said. "This will be a challenge in all settings because hospitals even in big cities do not have storage facilities for a vaccine at that ultra-low temperature."

That includes the Mayo Clinic, one of the biggest hospitals in the United States, which does not currently have the ability to store the vaccine at extremely low temperatures, Reuters reports.

"We're talking about a vaccine that needs storage at minus 70 or 80 [degrees Fahrenheit]. That's a tremendous logistical issue not only in the U.S. but outside the Western world," Gregory Poland, a virologist and vaccine researcher at the Clinic, said. "We're a major medical center and we don't have storage capacity like this. That will be true for everybody. This is a logistical obstacle."

It will especially be an obstacle for rural health care facilities, Claire Hannan, executive director at the Association of Immunization Managers, said.

"If Pfizer's is the only vaccine to be authorized in the next few months, we do worry about equity when it comes to spreading it to rural areas," she said.

Onisis Stefas, chief pharmacy officer for Northwell Health, said the health system is expanding its ultra-cold storage capacity to smoothly distribute the vaccine once it's approved.

"I think it will be difficult, but based on the task and how important it is, people will do the best to their ability to make that happen," Stefas said (Popken, NBC News, 11/9; Colchester/Hinshaw, Wall Street Journal, 11/10; O'Donnell, Reuters, 11/9).