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What you need to know about the COVID-19 vaccines

In December 2020, the Food and Drug Administration (FDA) issued emergency use authorizations (EUAs) for two vaccines for the prevention of the coronavirus disease (COVID-19)—one from pharmaceutical company Pfizer-BioNTech and one from pharmaceutical company Moderna. The EUA authority gives the FDA the ability to allow unapproved medical products to be used in an emergency to prevent life-threatening diseases. The FDA issued the EUAs after an extensive review process that determined both vaccines were safe for use.

When will the vaccines be available?

The Centers for Disease Control and Prevention (CDC) Advisory Committee on Immunization Practices has released recommendations for allocation of the vaccines. However, each individual state ultimately has the authority to decide which groups of people will be prioritized. Some counties have created a system through which residents can register to be notified as to when they will be able to receive a vaccine. Anyone who wants to know if such a system is in place should contact their local government.

The following is detailed information about the individual vaccines:


This vaccine has been approved for use in people 16 years of age and older. It contains messenger RNA (mRNA), which is genetic material that contains a small amount of the virus that instructs the cells in the body to make the virus’s distinctive “spike” protein. This causes the body to make copies of the protein, which teaches the immune system how to protect itself against the virus.

During clinical trials for the vaccine, Pfizer found it was 95 percent effective in preventing COVID-19. However, for it to be effective, people must receive it in two doses, with the second dose occurring 21 days after the first. The effectiveness was measured starting from seven days after the dose was administered.


This vaccine has been approved for use in people 18 years of age and older, though the company has recently begun testing it in 12- to 17-year-olds. Like the Pfizer-BioNTech vaccine, it contains mRNA, which teaches the body to protect itself from the virus. Also like the other vaccine, recipients must have two doses for it to be effective. For the Moderna vaccine, those two doses must be 28 days apart. During clinical trials, Moderna found that it was 94 percent effective in preventing COVID-19, measured starting from 14 days after the second dose.

For both vaccines, the most common side effects include injection site pain, fatigue, headache, muscle pain and joint pain—all of which are signs that a person’s immune system has been stimulated to start working, not that the person has contracted COVID-19. Anyone who receives one of the vaccines should be aware that there is a high possibility he or she will feel unwell after the shot—particularly the second dose—and may want to plan to rest immediately following it.

The primary difference between the two vaccines is the circumstances under which they need to be stored. Moderna’s vaccine must be shipped and stored at -4 degrees Fahrenheit, which is the temperature of a regular refrigerator freezer. Pfizer’s vaccine must be shipped and stored at -94 degrees Fahrenheit, which requires special freezers that must be loaded with dry ice every five days. Such freezers are not available at most doctors’ offices or pharmacies.

Neither vaccine has been tested on women who are pregnant or lactating. Both Pfizer and Moderna tested their vaccines on pregnant animals and saw no concerning signs, but they do not yet have data from pregnant humans. Therefore, women who are pregnant should choose whether they want to be vaccinated after discussing the risks and benefits with their doctor. Find more COVID-19 resources and risk control recommendations at