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mRNA Vaccines for COVID-19

What are mRNA vaccines and how do they work to defend against COVID-19?

Frequently Asked Questions

The use of messenger RNA (mRNA) in medical interventions has been researched for the last 20 years, including in vaccines hoping to fight diseases such as cancer, rabies, Ebola and the Zika virus. That means the research was ready to be applied to this new disease, COVID-19. With the recent authorization of two mRNA vaccines for emergency use to fight COVID-19 and more vaccine candidates in development, we can build protection against the virus in our communities if enough people are vaccinated.

What Is COVID-19?

COVID-19 is an infectious disease caused by a strain of coronavirus discovered in 2019, called SARS CoV-2. The disease is typically spread through respiratory droplets in the air from an infected person. SARS CoV-2 causes a range from no symptoms to severe symptoms, including fever, cough, fatigue, and breathing difficulty. Coronaviruses are a family of viruses that cause a number of different diseases, including COVID-19. Coronaviruses get their name because of the shape of the viruses, which have spiky proteins that resemble a crown. In Latin, “corona” means crown. This unique shape allows the virus to attach itself to the cells in our eyes, mouth, nose and throat and immediately start to multiply. The COVID-19 outbreak is defined as a pandemic, because it has spread across multiple countries and has affected a large number of people. An epidemic is when a disease outbreak occurs in a specific geographic area.

What Is mRNA and How Does it Work in a Vaccine?

Messenger RNA, or mRNA, are molecules within the body that contain genetic instructions for cells to make proteins that are required for the body to function properly. MRNA vaccines deliver synthetic mRNA molecules into cells, instructing them to make antigens. An antigen is a foreign invader that the immune system recognizes as not being part of itself, such as the protein surface of a virus. In the case of the COVID-19 mRNA vaccines, cells are instructed to only make the SARS Cov-2 spike protein, which is just enough to activate the immune system. But the cells are not given enough instructions to make a full virus, so the vaccine cannot cause COVID-19. Unlike conventional vaccines, mRNA vaccines do not use a weakened or killed virus. These antigens then trigger the immune system to produce specific protective antibodies that neutralize the virus–in this case, the antibodies needed to fight COVID-19. So if a person is exposed to COVID-19, the immune system will detect the familiar antigens and produce antibodies to attack them. A vaccinated person’s immune system can better defend against the infection altogether or greatly reduce the severity of the infection.

How Many Doses of the mRNA Vaccine Are Required?

The two mRNA vaccines for COVID-19 that have received emergency use authorization in the U.S. require two doses, three to four weeks apart, to be effective. With these vaccines, if the body only encounters the antigen once, it’s unclear how long the protection would last. Encountering the same antigen again in a short time boosts the abundance of protective antibodies on standby, so people are safeguarded for as long as possible. Like many vaccines for other common diseases, people may need to get vaccinated for COVID-19 again in the future. The frequency would depend on a variety of factors, including how much of the population receive the vaccine and how long the body retains the antibodies. Researchers are still learning how long these mRNA vaccines may provide protection.

How Does a Vaccine Help Build Herd Immunity?

For many years, vaccines have been preventing illness, saving countless lives, and have greatly reduced or eliminated several diseases around the world. Advancements in vaccines are some of the greatest public health achievements over the last century. The only way we can build enough protection in our communities is if the majority of people receive the vaccine. It's important to note that vaccinations and herd immunity are not two separate approaches to fighting a pandemic. Herd immunity occurs when a large portion of a community (the herd) becomes immune to a disease, making the spread of disease from person to person unlikely. Vaccines are used to help populations reach herd immunity faster.

How Will the Vaccines Be Distributed?

Vaccine distribution is a massive undertaking, involving federal, state, and local officials, carriers like UPS and FedEx, local pharmacies, and more. Even suppliers of dry ice are part of the operation, since the vaccines need to be stored at such low temperatures. After a vaccine is given emergency use authorization by the FDA, doses are allocated to states and tribal governments and then administered to priority groups. To learn more about your state’s plan, find it on the list created by the Kaiser Family Foundation.

The CDC recommended on December 3 that in the very first phase of distribution, known as Phase 1a, the vaccine should be offered to health care personnel and residents of long-term care facilities. The CDC advisory committee recommended on December 20 that if vaccine supply is limited the groups that should be offered vaccination next, in Phase 1b, are people over age 74 and frontline essential workers, such as those working in grocery stores. The advisory committee recommended Phase 1c consist of people aged 65–74 years, people aged 16–64 years with high-risk medical conditions, and other essential workers.

The earliest projection that a vaccine may be available to low-risk members of the general public is spring of 2021. It is important to remember that CDC recommendations for vaccine prioritization are influential but not mandatory, and each state and tribal government will create its own distribution plan.

Do I Still Need to Get Vaccinated if I Already Had COVID-19?

Yes. The CDC recommends getting vaccinated even if you have already had COVID-19, because you can get infected more than once. You may have short-term antibodies for protection after recovering from COVID-19, but we don’t know how long this protection lasts. Also there were no concerns reported from the clinical trials if a participant had COVID-19 and was also vaccinated.

Are There Certain People Who Should Not Receive the Vaccine?

Very few, but individuals with known history of a severe allergic reaction (e.g., anaphylaxis) to any component of the COVID-19 vaccine should not receive the vaccine. In addition, consider speaking with your doctor to make the decision if:

  • You are immunocompromised, meaning you have a known impaired immune system
  • You are pregnant or breastfeeding
  • You have a history of severe allergic reaction such as anaphylaxis to any vaccine or injectable therapy
  • You are currently a participant in a gene therapy clinical trial

The vaccine is currently not being given to children under the age of 16, but with more pediatric clinical trial data, it may eventually be available to younger ages.

If I Have a Rare Disease, Will the Vaccine Affect My Eligibility to Receive Gene Therapy in the Future?

If you are immunocompromised, speak with your provider to make the decision about getting vaccinated. However, there is no use of a virus or viral vector with the mRNA vaccines, so receiving an mRNA vaccine will not prevent you from obtaining a gene therapy in the future for your rare disease.

If I Am Currently a Participant in a Gene Therapy Clinical Trial Can I Get the Vaccine?

Check with your provider of the gene therapy trial for confirmation before receiving the vaccine.

Will the Vaccine Stop Me From Spreading the Virus to Others?

While clinical trial data shows that these mRNA vaccines do a very good job at preventing symptomatic COVID-19, data is still being collected to understand how well the vaccine prevents asymptomatic infection (infection without symptoms). Research is ongoing to determine whether a vaccinated person might still be able to asymptomatically transmit COVID-19 to someone else who is not vaccinated. This is why it is important for a large proportion of the population to be vaccinated.

How Was the mRNA Vaccine Produced and Tested So Quickly? 

Lipid nanoparticles encase the mRNA to protect it before it enters the cell.The mRNA vaccines for COVID-19 have been developed at a record-setting speed, but that doesn’t mean that they aren’t tested to the same safety and efficacy standards as other medical interventions. Before it is made widely available, any vaccine needs to be first studied in clinical trials and then reviewed and authorized by an agency that oversees the safety and effectiveness of medical products. In the United States, this is done by the Food and Drug Administration (FDA). Starting a clinical trial for any medical intervention requires a research team, adequate funding and resources, and enough initial patients and data to properly plan the study. It’s a daunting task and is often why research and development take so long. Because this disease is a global health emergency, funding has been quickly directed toward reducing many of these barriers. The goal is to treat this dangerous disease as soon as possible, and as COVID-19 infection rates increased in 2020, researchers were able to accumulate a wealth of data and eager volunteers for clinical trials.

How Effective Are the mRNA Vaccines?

Based on clinical trials, researchers and health experts have found the results to be positive. The mRNA vaccines were shown to reduce the risk of adults getting COVID-19 by over 90 percent. Moderna’s study involved more than 30,000 participants in the U.S. and was 94.5 percent effective at reducing the risk of getting COVID-19, with only five cases found in the vaccinated group versus 90 in the non-vaccinated group. Racially and ethnically diverse backgrounds were achieved, making up 37 percent of U.S. participants. Almost 25 percent of participants were over the age of 65, and just over 15 percent of people had high-risk medical conditions like diabetes and heart disease. Pfizer and BioNTech’s vaccine involved over 43,000 participants globally and was 95 percent effective at reducing the risk of getting COVID-19, with only eight cases appearing in the vaccinated group versus 162 in the non-vaccinated group. Racially and ethnically diverse backgrounds were achieved, making up 30 percent of U.S. participants and 42 percent of participants in other countries. The trial also had participants in the high-risk age group of 56-85 years old, which made up 45 percent of U.S. participants and 41 percent globally.

Are There Any Side Effects of the COVID-19 Vaccine?

Like any medical intervention, vaccines can cause side effects, which are known from studies to be caused by the vaccine. This often means that your immune system is doing its job and any mild symptoms typically last only a few days. Side effects are a type of adverse event. An adverse event is any health problem ranging from minor to serious, that happens after vaccination, whether it is caused by the vaccine or not. During testing in clinical trials, mRNA vaccines had not caused any serious adverse events. There have since been isolated  incidents of rapid onset of allergic reaction, and of facial swelling in participants who had previously received botox; all cases were treatable, and the participants have recovered. Sites that are administering vaccines are now required to have appropriate medical treatments immediately available for severe allergic reactions. Moderna announced that less than 10 percent of participants who received the vaccine reported short-lived feelings of fatigue, headache, achiness, and muscle pain. The Pfizer and BioNTech vaccine also resulted in no serious safety concerns observed, with less than 4 percent of participants reporting fatigue or headache. Though unlikely, if you have any symptoms that concern you after you are vaccinated, call your doctor.

What Are Clinical Trials?

Clinical trials are a required research process that studies the way an intervention interacts with the body. Clinical trials typically take many years, and are divided into different phases that answer specific questions about the treatment, primarily whether it is safe and effective. However, the FDA has created expedited pathways and programs to accelerate the process while still maintaining the same high standards. This is typically done for drugs and therapies for serious diseases with no other treatment options, or for public health emergencies— fitting for interventions that fight COVID-19.

What is Emergency Use Authorization?

During a declared public health emergency, such as the COVID-19 pandemic, treatment and vaccine developers can apply for an Emergency Use Authorization (EUA) from the FDA. An EUA allows the use of unapproved medical products or unapproved uses of approved medical products to prevent serious or life-threatening diseases during a public health emergency. An EUA for a vaccine must meet certain required criteria, including that there are no adequate, approved, or available alternatives and that benefits outweigh risks. The FDA evaluates whether the criteria is met for each application they receive and takes into account all the scientific evidence about the vaccine. So far two vaccines, developed by Moderna and Pfizer/BioNTech, have been granted EUA status in the United States.

Why Does the Vaccine Need To Be Kept Cold?

An important element of mRNA vaccine production is storage. Like many existing vaccines, the Moderna and Pfizer/BioNTech mRNA vaccines for COVID-19 need to be kept cold before use. However, these two vaccines require much colder storage than most existing vaccines in order to keep the mRNA molecules from degrading. Moderna’s vaccine must be transported and stored at -4 degrees Fahrenheit (-20 degrees Celsius), while the Pfizer/BioNTech vaccine needs to be kept at -94 degrees Fahrenheit (-70 degrees Celsius). Both vaccines can then be thawed shortly before administration. Overcoming shipment and storage challenges will therefore be very important for mRNA vaccine use, especially in countries that do not have existing ultra-cold storage facilities.

Are There Different Kinds of COVID-19 Vaccines Being Developed?

There are currently two different mRNA vaccines for COVID-19 that have received emergency use authorization from the FDA. One vaccine is created by the biotechnology company Moderna and the other by pharmaceutical corporations Pfizer and BioNTech. It’s common to have multiple treatments or preventive medicines in development and having more than one option creates a variety of benefits. We will need more than one company with an approved vaccine to manufacture the number of doses  needed for worldwide vaccination. More vaccine approvals help to increase patient access, and some vaccine approaches may work better in certain populations. There are other vaccine approaches being developed that don’t utilize mRNA. For example, there are vaccine candidates using adenovirus vectors to deliver DNA into cells, instructing them to create antibodies and start the immune system’s response for COVID-19. There are additional approaches being researched that do not fall under the umbrella of gene therapy.

Where Can I Find Additional Information?

The Centers for Disease Control and Prevention (CDC),the U.S. Food and Drug Administration (FDA), and the World Health Organization (WHO) offer credible resources about COVID-19 and mRNA vaccines for COVID-19.

Last Updated: 01/20/2021