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Vaccine trials are in full swing in an effort to find a shot at beating COVID-19. But who will get the first inoculations?

It’s a complicated equation hinging on shipping, storage, availability and risk level. Combine all of this with trial results for different vaccine candidates and the Centers for Disease Control has come up with a COVID-19 vaccine dosing schedule that could have millions getting their shot by December.

As students head back to school and employers increasingly welcome returning workers it becomes even more critical for herd immunity.

The key to that lies in a vial with an injection that offers immunity to SARS-CoV2, the virus that causes COVID-19.

There are several candidates scientists at various pharmaceutical companies and universities are giving to study participants. As Phase 3 trial results begin to trickle in, experts say every state should prepare to invite residents to get their vaccine as early as October. The process tested and perfected back in the 2009 H1N1 flu pandemic.

Tinglong Dai, who has a PhD, is an associate professor at Johns Hopkins University.

“I think the infrastructure is there. So suppose we have a reasonable amount of supply in the beginning, I think it could be a smooth process,” Dai said.

The federal government will initially buy all available, viable vaccines. Medical offices, hospitals and pharmacies must enroll in the vaccination program for the right to administer the initial shots, confirming they have staff and proper facilities

The CDC Advisory Committee on Immunization Practices said as those vaccine doses are shipped across the country, they should go immediately to big cities with large populations. Frontline medical workers and first responders, older people and those with co-morbidities like asthma, diabetes, heart disease, high blood pressure and obesity will get priority since they are likely to get sicker with a COVID-19 diagnosis.

Dr. Mike Ison is with Northwestern Medicine Infectious Diseases.

“There will have to be entire processes developed to figure out how we are going to get patients identified,” he said. “What is challenging is we have a lot of people at high risk who may not be tied into healthcare and how are they going to know to come in where to go how easy is it too bring patients in?”

Most of the experimental vaccines require two doses given a month apart. So far two of seven study vaccines are rising to the top. A third promising trial was halted just this week as a study participant got sick.

The two leading candidates do not have preservatives and therefore they are temperature sensitive.

Moderna’s vaccine arrives at -4 degrees Fahrenheit and can be stored for two weeks in a regular refrigerator. But Pfizer’s shot requires a -94 degree storage temperature which may impact where it’s distributed in mass. Pfizer will ship doses in special containers with dry ice which must be replaced every five days. Hospitals typically have sufficient cold storage.

“This is going to be more complicated depending on the vaccine some of the vaccines have to be frozen in liquid nitrogen or at very low temps and most clinical practices don’t have the capacity to deal with that,” Ison said.

In addition to vaccines, supply kits with needles, syringes, alcohol pads and surgical masks will be shipped to distribution sites.

Here’s the potential schedule: If both vaccines are proving safe in trials, 3 million doses will be shipped in October. That ramps up to 20-30 million in November with another 45 million arriving in December. For a total of potentially 78 million vaccinations.

If there is a hitch with either top candidate, only 1-2 million doses will go out in October. With 10-20 million by November and 15-30 million by December. In the best case scenario here, 52 million people will get a vaccine.

“I think it is very, very important to have a really transparent process, a really transparent reporting procedure for any incidents related to vaccination,” Dai said. “Because only when this process is very transparent, only when safety is closely monitored, can people be confident about safety of this vaccine.”

All of this depends on the current trials continuing without delay and the manufacturing process running smoothly. If so, for many, a new year’s gift of immunity from COVID-19 may be on the horizon along with a return to a more normal life in 2021.

Meantime doctors advise, in the absence of a COVID-19 vaccine for everyone, it is even more critical to get a flu shot this year.