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And where there is evidence of side effects ranging from mild to severe, the more serious side effects are rare. All data and statistics are based on publicly available data at the time of publication. Some information may be out of date. Visit our coronavirus hub for the most recent information on the COVID-19 pandemic. The above information comes from the Centers for Disease Control and Prevention (CDC). The agency currently approves three types of COVID-19 vaccines for their safety and effectiveness:mRNA vaccinesvector vaccinesprotein subunit vaccines However, in the United States, protein subunit vaccines are not in common use compared with other types. This article explores how the vaccine works, the different types, and the benefits and risks of each. Some people may experience mild side effects that can last for a few days. However, very few individuals may experience severe side effects, such as anaphylaxis, and require immediate medical attention. If these serious side effects occur, a person should dial 911 or consult an emergency department. Anaphylaxis is a severe allergic reaction that can be life threatening. The symptoms develop suddenly and include:hivesswelling of the face or mouthwheezingfast, shallow breathinga fast heart rateclammy skinanxiety or confusiondizzinessvomitingblue or white lipsfainting or loss of consciousness If someone has these symptoms:Check whether they are carrying an epinephrine pen. If they are, follow the instructions on the side of the pen to use it.Dial 911 or the number of the nearest emergency department.Lay the person down from a standing position. If they have vomited, turn them onto their side.Stay with them until the emergency services arrive. Some people may need more than one epinephrine injection. If the symptoms do not improve in 5–15 minutes, or they come back, use a second pen if the person has one. How the vaccines work Share on PinterestChip Somodevilla/Getty ImagesThe COVID-19 vaccine conditions a person’s immune system to respond to SARS-CoV-2, the virus that causes the disease, without causing an infection. Since 2020, laboratories worldwide have developed different vaccines that serve the same purpose. When SARS-CoV-2 passes from one person to another, it causes an infection that attacks the body. The immune system uses white blood cells to defend the immune system. Of the overall white blood cells in the body, lymphocytes make up 25% of them. There are two main categories of lymphocytes: B lymphocytes and T lymphocytes. The following types of white blood cells perform the functions below: Macrophage: Fight the infection by removing germs and cells that are no longer functional. They leave behind parts of the germs, known as antigens. The body identifies these as dangerous and stimulates “attacking” antibodies.B lymphocytes: These produce antibodies, follow the macrophages, and attack part of the virus that remains.T lymphocytes: This type of defensive white blood cell attacks healthy body cells that carry infections. After a viral infection, some lymphocytes that have attacked the virus remain in the body, ready to respond if the infection returns. The T lymphocytes recognize the virus act quickly if the body encounters the same virus. The B lymphocytes recall how to fight it and produce antibodies to attack the virus. It takes a few weeks after vaccination for the body to produce these T lymphocytes and B lymphocytes. What we know so far COVID-19 is still a relatively young virus, and the development of vaccines was a rapid process. However, coronaviruses are not new. For many years, research has been developing vaccines for similar viruses, such as Middle East respiratory syndrome coronavirus (MERS-CoV) and severe acute respiratory syndrome coronavirus (SARS-CoV). Despite their fast production, the approved vaccines for COVID-19 have undergone the necessary clinical trials. Additionally, there have been tens of thousands of participants in each of these trials. As of March 30, 2022, over 217 million people in the U.S. have received both vaccine doses. Additionally, over 97 million individuals have had a booster dose of the vaccine. However, the vaccine can cause side effects, such as fever and pain in the injection site. That said, they generally do not last longer than 2 days and are rarely serious. Side effects come from the process of the body building immunity. The following manufacturers have produced vaccines that currently have approval in the U.S.:PfizerModernaJohnson and Johnson Safety and risks of Pfizer Pfizer-BioNTech has manufactured a messenger RNA, or mRNA, vaccine. The vaccine works by using a piece of mRNA to instruct cells in the body on how to create a certain protein. This protein then generates an immune response, during which the body produces the antibodies that will fight the live virus if there is an infection. The Pfizer vaccine is safe for people aged 5 years and older. Any side effects are generally mild and occur within a few days of receiving the vaccine. However, the Pfizer vaccine can cause complications for certain people. Individuals should not have the vaccine if they are allergic to any of its ingredients. If there is an allergic reaction after the first dose, they should not have a second dose of the mRNA vaccine. In rare cases, young people have experienced myocarditis, which refers to inflammation of the heart, or pericarditis, which involves inflammation of the tissue surrounding the heart, after having the Pfizer mRNA COVID vaccine. Safety and risks of Moderna Similar to the Pfizer vaccine, the Moderna vaccine is an mRNA vaccine. It is appropriate for people who are 18 years of age or older. As with the Pfizer vaccine, the Moderna vaccine can pose a risk for people who are allergic to the ingredients. If a person has an allergic reaction from the first mRNA dose, they should not have a second dose of Moderna. In rare situations, young people have experienced myocarditis or pericarditis after having the Moderna mRNA vaccine. Safety and risks of Johnson and Johnson Johnson and Johnson’s Janssen vaccine is a viral vector vaccine. These types of vaccines work by putting molecules called antigens from one virus into a completely different virus. It enables these antigens to mimic the infection as they enter the cells, triggering an immune response. The Johnson and Johnson vaccine is appropriate for individuals who are 18 years of age or older. It has higher safety risks than the other two types, as there may be a link between the Johnson and Johnson vaccine and blood clots. However, the likelihood is extremely low, affecting a rate of 3.83 people in every million. In some cases, it has been fatal. Additionally, individuals should avoid the vaccine if they are allergic to any of its ingredients. They should also not have a second dose of the same vaccine if they have an allergic reaction to the first. Despite some health implications, the Johnson and Johnson viral vector vaccine is generally safer than not having a vaccine, and it is the best option for people at risk from mRNA vaccines. Severe and rare side effects of the vaccines There are rare cases where people have experienced adverse effects after receiving the COVID-19 vaccine. The link between these effects and the vaccine is not certain. These effects are:anaphylaxismyocarditispericarditisGuillain-Barré Syndromethrombosis with thrombocytopenia syndrome (TTS) As of May 5, 2022, the FDA changed the Emergency Use Authorization (EUA) granted to the Johnson & Johnson vaccine, limiting authorization. This decision follows an analysis of the safety concerns regarding thrombosis with thrombocytopenia syndrome (TTS). Authorization of the Johnson & Johnson vaccine is now limited to people ages 18 years and older who can’t receive other approved COVID-19 vaccines or who would choose not to get vaccinated otherwise. Individuals who cannot receive other COVID-19 vaccines includes those for whom it is not clinically appropriate or who don’t have access to the Moderna or Pfizer vaccine. If a person experiences a rare side effect from the vaccine, they should seek medical assistance immediately or dial 911. Additionally, they can report the incident to the Vaccine Adverse Event Reporting System after recovery. Benefits outweigh risks Overall, the benefits of any COVID-19 vaccine are greater than its potential risks, which are rare. However, certain individuals may be at more risk, such as those with certain allergies, so they should ensure they choose an appropriate vaccine for their needs. They can consult a doctor to discuss their options for getting vaccinated. Note that the risk of death or hospitalization from COVID-19 is considerably higher than the risk of such effects from the vaccine. Summary COVID-19 vaccines effectively enable the body to build up immunity to the virus without having an infection. Though researchers developed these vaccines rapidly, those vaccines that currently have approval in the U.S. have undergone all the necessary clinical trials. Scientists developed these vaccine production techniques before the discovery of COVID-19, using the principles from managing other coronaviruses, such as SARS and MERS. Overall, the advantages of the Pfizer and Moderna mRNA vaccines and the Johnson and Johnson viral vector vaccine outweigh the risks. Last medically reviewed on March 30, 2022Immune System / VaccinesCOVID-19 12 sourcescollapsedMedical News Today has strict sourcing guidelines and draws only from peer-reviewed studies, academic research institutions, and medical journals and associations. We avoid using tertiary references. We link primary sources — including studies, scientific references, and statistics — within each article and also list them in the resources section at the bottom of our articles. You can learn more about how we ensure our content is accurate and current by reading our editorial policy.Coronavirus (COVID-19) update: FDA limits use of Janssen COVID-19 vaccine to certain individuals. (2022).https://www.fda.gov/news-events/press-announcements/coronavirus-covid-19-update-fda-limits-use-janssen-covid-19-vaccine-certain-individualsCOVID data tracker. (2022).https://covid.cdc.gov/covid-data-tracker/Developing COVID-19 vaccines. (2022).https://www.cdc.gov/coronavirus/2019-ncov/vaccines/distributing/steps-ensure-safety.htmlJanssen COVID-19 vaccine. (2022).https://www.fda.gov/emergency-preparedness-and-response/coronavirus-disease-2019-covid-19/janssen-covid-19-vaccineJohnson & Johnson's' Janssen COVID-19 vaccine overview and safety. (2022).https://www.cdc.gov/coronavirus/2019-ncov/vaccines/different-vaccines/janssen.htmlLau, C. L., et al. (2022). Risk–benefit analysis of COVID-19 vaccines - A neurological perspective.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8687148/Li, Y.-D., et al. (2020). Coronavirus vaccine development: From SARS and MERS to COVID-19.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7749790/Moderna COVID-19 vaccine (also known as Spikevax) overview and safety. (2022).https://www.cdc.gov/coronavirus/2019-ncov/vaccines/different-vaccines/Moderna.htmlPfizer-BioNTech COVID-19 vaccine (also known as COMIRNATY) overview and safety. (2022).https://www.cdc.gov/coronavirus/2019-ncov/vaccines/different-vaccines/Pfizer-BioNTech.htmlStay up to date with your COVID-19 vaccines. (2022).https://www.cdc.gov/coronavirus/2019-ncov/vaccines/different-vaccines.htmlTigner, A., et al. (2021). Histology, white blood cell.https://www.ncbi.nlm.nih.gov/books/NBK563148/Understanding how COVID-19 vaccines work. (2022).https://www.cdc.gov/coronavirus/2019-ncov/vaccines/different-vaccines/how-they-work.htmlFEEDBACK:Medically reviewed by Darragh O'Carroll, MD — By Helen Millar on March 30, 2022 Latest newsWhat sets 'SuperAgers' apart? 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