As health care professionals administer COVID-19 vaccines throughout the United States, many people have questions, including who is eligible to be vaccinated and how the vaccines work. Here are answers to some frequently asked questions about the vaccines, including additional insight from Armando Meza, M.D., chief of infectious diseases at the Texas Tech University Health Sciences Center El Paso Foster School of Medicine.

No. The Pfizer, Moderna, and Johnson & Johnson vaccines do not contain live versions of the COVID-19 virus. 
Though there is no known timespan for the vaccine’s effectiveness, Dr. Meza estimates the vaccine’s protection will likely last at least one year, if not longer.

Yes. Currently, there’s no firm data on how long immunity lasts after a patient is infected with COVID-19. Because re-infection is possible, the vaccine is suggested for further protection.

Per the CDC, Pfizer, Moderna, Johnson & Johnson, and the Texas Department of State Health Services, below are more answers to frequently asked questions about COVID-19 vaccines.

The FDA authorized two vaccines for emergency use authorization in December 2020. The Pfizer and BioNTech vaccine (commonly referred to as the Pfizer vaccine) was authorized by the FDA on Dec. 11, 2020.  The Moderna vaccine was authorized by the FDA on Dec. 18, 2020. For maximum effectiveness, the vaccines are administered in two doses: 21 days apart for the Pfizer vaccine and 28 days apart for the Moderna vaccine.

On Feb. 27, 2021, the FDA authorized emergency use authorization for a third vaccine, Johnson & Johnson's Janssen COVID-19 vaccine. 

As of May 10, 2021, the FDA authorized Pfizer's COVID-19 vaccine for EUA in adolescents 12 to 15 years old, making the vaccine available to both youth and adults. The City of El Paso has made the Pfizer vaccine available to this age group. Previously the vaccine was only available to those 16 and older. 

Moderna and Johnson & Johnson's vaccines are currently only available for those 18 years of age and older. 

For the Pfizer vaccine, the most common adverse reactions reported were temporary, mild pain at the injection site, fatigue and headache. These side effects generally resolved within two days, according to Pfizer’s large-scale study of more than 40,000 participants. These reactions were less common and milder in older adults than younger adults.

There have been reports of allergic reactions in a handful of people who were vaccinated with the Pfizer vaccine in Britain and Alaska. The FDA has issued a precaution for people with a history of severe allergic reaction to vaccines; they may still receive the vaccine, but health care workers should counsel them on the risks and benefits of receiving the vaccination.

The Moderna study found that most common side effects were mild and included injection-site pain, fatigue, headache and chills. Severe adverse reactions were rare but occurred more frequently after the second dose.

After a brief halt of the use of the Johnson & Johnson vaccine, the CDC and FDA recommended the continued use of the vaccine effective April 23, 2021. However, women younger than 50 should be aware of the rare risk of blood clots with low platelets after vaccination. If you've received the Johnson & Johnson vaccine, here's what you should know. For more information, read the CDC/FDA statement regarding the safe use of the Johnson & Johnson vaccine. 

Common side effects of the Johnson & Johnson vaccine include pain, redness and swelling in the arm where you received the shot, fatigue, headache, muscle pain, chills, fever and nausea. 

For maximum effectiveness, the vaccines require two doses: 21 days apart for the Pfizer vaccine and 28 days apart for the Moderna vaccine. Only one dose is required for the Johnson & Johnson vaccine. 

According to CDC recommendations, fully vaccinated individuals (2 weeks after the second of a two-dose vaccine, or 2 weeks after a one-dose vaccine)  can resume activities without wearing a mask or physicially distancing, except where required by federal, state, local, tribal or territorial laws, rules and regulations, including local business and workplace guidance. 

However, due to the delta variant, the CDC recommends wearing a face mask in all public indoor settings in areas of substantial or high transmission, regardless of vaccination status. 

The CDC suggests that those with an immune-weakining condition, or who take medication that weakens the immune system, should talk to their health care provider before easing precautions after being fully vaccinated.

The Pfizer and Moderna vaccines are known as mRNA vaccines. They have strands of genetic material called mRNA inside a special coating. That coating protects the mRNA from enzymes in the body that would otherwise break it down. It also helps the mRNA enter the muscle cells near the vaccination site in the upper arm.

The vaccines give instructions for our cells to make a harmless piece of what is called the “spike protein.” The spike protein is found on the surface of the virus that causes COVID-19.

Once the instructions (mRNA) are inside the immune cells, the cells use them to make the protein piece. After the protein piece is made, the cell breaks down the instructions and gets rid of them.

Next, the cell displays the protein piece on its surface. Our immune systems recognize that the protein doesn’t belong there and begin building an immune response and making antibodies, like what happens in natural infection against COVID-19.

At the end of the process, our bodies have learned how to protect against future infection. The benefit of mRNA vaccines, like all vaccines, is those vaccinated gain this protection without ever having to risk the serious consequences of getting sick with COVID-19.

They are new, but not unknown. Researchers have been studying and working with mRNA vaccines for decades. Interest has grown in these vaccines because they can be developed in a laboratory using readily available materials. This means the process can be standardized and scaled up, making vaccine development faster than traditional methods.

Future mRNA vaccine technology may allow for one vaccine to provide protection for multiple diseases, thus decreasing the number of shots needed for protection against common vaccine-preventable diseases.

The Johnson & Johnson vaccine is a viral vector vaccine which uses a modified version of a different virus (the vector) to deliver important instructions to cells. The benefit of viral vector vaccines, like all vaccines, is those vaccinated gain protection without having to risk the serious consequences of getting sick with COVID-19. 

First, the vector (not the virus that causes COVID-19, but a different, harmless virus) will enter a cell in our body and then use the cell’s machinery to produce a harmless piece of the virus that causes COVID-19. This piece is known as a spike protein and it is only found on the surface of the virus that causes COVID-19.

Next, the cell displays the spike protein on its surface, and our immune system recognizes it doesn’t belong there. This triggers our immune system to begin producing antibodies and activating other immune cells to fight off what it thinks is an infection.

At the end of the process, our bodies have learned how to protect us against future infection with the virus that causes COVID-19. The benefit is that we get this protection from a vaccine, without ever having to risk the serious consequences of getting sick with COVID-19. Any temporary discomfort experienced after getting the vaccine is a natural part of the process and an indication that the vaccine is working.

Additional facts about COVID-19 viral vector vaccines: 

  • They cannot give someone COVID-19 or other infections. 
  • Viral vectors cannot cause infection with COVID-19 or with the virus used as the vaccine vector. 
  • They do not affect or interact with DNA in any way. 
  • The genetic material delivered by the viral vector does not integrate into a person's DNA.