Editor's note: Information on the COVID-19 crisis is constantly changing. For the latest numbers and updates, keep checking the CDC's website. For the most up-to-date information from Michigan Medicine, visit the hospital's Coronavirus (COVID-19) webpage.

Almost immediately after the SARS-CoV-2 virus was identified in January 2020, scientists got to work on a vaccine. In less than a year, one of top candidate vaccines, from Pfizer and BioNTech, was granted Emergency Use Authorization by the U.S. Food and Drug Administration. A second vaccine from Moderna Inc. and NIH is likely to soon follow. Both vaccines use mRNA technology.

Sandro Cinti, M.D., Professor of Infectious Disease at University of Michigan Medical School likens an mRNA vaccine to "Tom Cruise's character in Mission Impossible." Like an undercover spy, the vaccine's mission is to get into the cell, deliver instructions and then self-destruct. The instructions are a small piece of genetic code, the mRNA, for the coronavirus' spike protein. "The spike protein is an antigen, which is the piece of the virus we want an immune response to," Cinti explains.

The body's immune system recognizes that protein as an attack and ramps up to fight it off. The vaccine tricks the body into reacting to a harmless set of instructions so that if you encounter the virus again, your body already knows how to fight it.

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The Pfizer and Moderna viruses were shown to be over 90% effective in the more than 30,000 people who received one of the vaccines in a Phase 3 clinical trial.

What's in the COVID-19 vaccine?

The vaccine contains more than just mRNA, of course. Unlike what some online rumors have stated, the vaccine does not contain tracking devices, fetal tissue or any live virus. It won't give you COVID-19. Michigan Medicine's Chief Pharmacy Officer Stan Kent, RPh, explains that beyond the mRNA instructions themselves, the vaccine contains a fatty coating to protect the mRNA (which is delicate and sensitive to heat and light), salts to maintain proper pH and a stabilizing sugar. And those concerned about the mRNA itself, need not be, says Kent. "If you think about it, any cell, whether it be from a plant or animal, has DNA and RNA in it. We're ingesting and breathing it in constantly."

Should there be concerns about allergic reactions to the COVID vaccine?

Shortly after vaccination began in the UK, there were news reports of two people having severe allergic reactions after getting the vaccine. "People can have allergic reactions to medicine, a vaccine, food but these are pretty rare," says Adam Lauring, M.D., Ph.D., Associate Professor of Internal Medicine and Microbiology and Immunology. "For instance, there are allergic reactions to the flu shot every year, but these reactions are short and manageable."

In fact, those getting the vaccine are observed for at least 15 minutes afterward to make sure they are okay. The CDC has also created an app called v-safe that patients can opt-in to report any side effects. Side effects that were common from the COVID-19 vaccine included injection site pain, tiredness, headache, fever among other mild effects.

Says Lauring, "I wouldn't say a couple of people with an allergic reaction among tens of thousands would be reason to be overly concerned about the safety of the vaccine."

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mRNA vaccines: Don't forget your second dose

Both the Pfizer and Moderna vaccines require two doses. In the early phases of the vaccine clinical trials, both groups looked to see how much of their vaccine was required to provide immunity, by looking at the amount of antibodies produced. They determined that two doses, one followed by another three to four weeks later, provided the best immunity with the fewest side effects. Though there was data that one dose offered some protection, "it's not something you can bank on and the amount of data to support that were not particularly strong," says Lauring. "I definitely would not encourage people to think that after the first dose everything is fine. You really need to show up for the second dose."

Special populations and the COVID vaccine

Certain groups who are eligible for COVID-19 vaccination may be wondering if the vaccine is safe for them, including people who are immunocompromised or who are pregnant or breastfeeding.

"There's no reason to believe the mRNA vaccine will have detrimental effects in someone who is immune compromised," says Cinti. The CDC Advisory Committee on Infection Practices, which recommended the vaccine for emergency use, notes that these people are at higher risk for severe COVID-19. Although there is no specific safety or efficacy data, people who are immunocompromised can receive the vaccine after discussing with their clinician. 

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"It's all about your risk," says Cinti. "If the risk of getting COVID-19 outweighs the risk of getting the vaccine, then you might want to get the vaccine."

Data have shown that people who are pregnant are also at higher risk for severe illness or death from COVID-19. With the potential devastating consequences of COVID-19 in mind, the CDC and the Society for Maternal-Fetal Medicine have recommended that pregnant women be offered the vaccine after a discussion with their doctor about risk and benefits.

Even as healthcare workers and others receive the first doses, the CDC, FDA and other researchers will continue to study the vaccines, gathering data to see how they perform in the real world.

"Any time there's a vaccine, there's a robust reporting system that monitors for adverse events that will continue to track these events in case there's something that pops up that wasn't seen in the clinical trial," says Lauring.

But, he says, there should be no question in taking a safe and effective vaccine during a pandemic.

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