Can you pick which Covid-19 vaccine to get? 1 factor will decide

When people get a flu vaccine, the company behind the shot isn't usually top of mind. But with coronavirus vaccines created in record-speed and on public display, Moderna and Pfizer have become household names. Both received Emergency Use Authorization from the FDA in December and both are now being distributed and used.

So the question is: Will you get to choose which one you get?

The answer is not really — at least, not anytime soon.

As long as vaccines remain in short supply, most people will not have a choice of which vaccine they receive, says William Schaffner, an infectious disease expert at Vanderbilt University Medical Center. It’s not a sure thing that every facility will have both vaccines on hand at all, let alone both at the same time.

“Certainly at this stage, each location that provides vaccines will have only one kind of vaccine,” Schaffner tells Inverse.

Decisions made by the federal government will determine how much of each vaccine every state gets, but at the local level, transportation and storage requirements will dictate what specific facilities get what vaccine.

That's the final step that determines what vaccine is available when you walk through the door.

"The main thing is the cold storage," Schaffner continues. "That's far and away what accounts for 99 percent of who's getting what."

What factors decide which Covid-19 vaccine I get?

The Pfizer and Moderna vaccines need to be transported and stored in different ways. This means some locations are a better fit for one vaccine compared to the other.

The Pfizer vaccine needs to be stored long-term temperature of -70 degrees celsius (-94 degrees Fahrenheit), which requires special freezers. If one of those isn't available, it can be stored for up to 30 days in a special cooler designed by Pfizer, provided it's refilled with dry ice every five days. If even that won't suffice, the vaccine can last for about 5 days in a normal refrigerator.

"We think the Moderna vaccine will be much more widely available than Pfizer’s."

Meanwhile, Moderna's vaccine can be stored for six months at a higher temperature of -20 degrees Celsius (-4 degrees Fahrenheit). It can last for 30 days in a normal refrigerator.

Because the Moderna vaccine has a longer shelf life at refrigerator temperature, Schaffner says that this vaccine is better suited for smaller facilities that don’t have specialized equipment. It's currently being delivered to spaces like local health departments, community hospitals, rural hospitals, and "eventually to pharmacists and doctors offices," he says.

“We think the Moderna vaccine will be much more widely available than Pfizer’s."

Pfizer’s vaccine, however, is suited for places like larger hospitals or clinics that have specialized freezers at their disposal. That's working to our advantage for now because the first round of vaccination is partially targeted towards healthcare workers who can receive the vaccine where they work.

It's also the large pharmacies, like CVS and Walgreens, that are tasked with delivering and administering vaccines at long-term care facilities, this week. The pharmacy chains will manage the cold-chain requirements for the vaccine and provide on-site clinics.

The minimum order volume for the Pfizer vaccine is 975 doses, which may be ideal for large hospitals vaccinating large numbers of people. But for smaller clinics, that’s a lot of vaccines to handle.

Modena can supply a vaccine in a minimum order of 100, which is, again, easier for small pharmacies, clinics, or doctor’s offices with limited space.

“When it comes time for the average person to get vaccinated, they're more likely to go to their doctor, or to the local health department or to a pharmacist. And I think those locations will have the Moderna vaccine,” Schaffner says.

Pfizer and Moderna vaccines: What’s the difference?

The Phase 3 clinical trial on the Pfizer vaccine showed it was about 95 percent effective in preventing Covid-19 disease. Moderna’s appears to be equally effective: It's 94.5 percent effective in preventing disease.

Neither vaccine, however, has been proven to prevent infection — which is why you'll still have to wear a mask post-vaccine, no matter which one you get.

Both vaccines also tend to have similar kinds of side effects, including headache, fever, or fatigue. But data from the Moderna vaccine trial suggest that more people experienced intense versions (enough to disrupt daily living) of headache and fatigue in that trial compared to Pfizer's. For instance, 9.7 percent of people in Moderna's trial experienced severe fatigue whereas 3.8 percent of people in Pfizer's trial experienced the same.

However, for right now, Schaffner calls the difference between both vaccines “small potatoes.” But that does not mean they are interchangeable.

These vaccines shouldn’t be mixed and matched. After receiving one brand of vaccine, it’s critical to stick to that brand when getting a second dose, says Schaffner, because there’s no data on how well vaccines perform when combined – at least not yet.

That second dose comes 21 days later for the Pfizer Vaccine and 28 days later for the Moderna vaccine.

What comes next — The FDA has indicated that both the Pfizer vaccine and the Moderna vaccine will continue to be studied. This will illuminate finer details about how well each one works in the wild. As those results come in, it could become clear that one vaccine works better in some populations. For now, both vaccines seem to perform comparably, Schaffner says.

The FDA is also keeping an eye on reports of severe allergic reactions to the Pfizer vaccine — six cases have been reported as of Saturday. No such reports have been seen for the Moderna vaccine just yet. That may also change as more people are vaccinated.

The CDC guidance still says that people with a history of allergies not related to vaccines should get the Pfizer vaccine. The National Institute of Health is also planning a study on patients with a history of allergic reactions to clarify what component of the Pfizer vaccine may be behind the reactions. This could help clarify the guidance in the coming weeks.

It's important to remember that there could be more vaccines on the way: There are still 18 vaccines in Phase 3 trials. And if those vaccines are also safe and effective, there may be a future where people choose which vaccines they get as supply increases.

For now, as the US rolls out a mass vaccination campaign, it’s the logistics that dictate which vaccine ends up in what area, and ultimately, which one is in the freezer when you walk through the door.