# Can the COVID-19 vaccine cause me to get sick? Canonical page: https://clinicsjo.com/en/faq/can-covid-19-vaccine-cause-illness Language: en Category: infectious Publisher: ClinicsJo Published: 2026-09-13T08:09:51.330Z Content updated: 2026-09-13T08:09:51.330Z Translation (ar): https://clinicsjo.com/ar/faq/can-covid-19-vaccine-cause-illness No, the COVID-19 vaccine (such as the Moderna vaccine) cannot cause you to develop COVID-19. Vaccines do not contain the live SARS-CoV-2 virus that causes the disease. Instead, vaccines work by teaching your immune system how to recognize and fight the virus, which reduces the risk of infection or limits its severity if you do contract it [\[1\]](). COVID-19 vaccines are intended to protect you from infection, reduce the likelihood of needing emergency care or hospitalization, lower the risk of severe illness or death, and also reduce the risk of long COVID [\[2\]](). ## How does the COVID-19 vaccine work? COVID-19 vaccines, such as mRNA vaccines, work by delivering a small piece of the virus's genetic material (not the virus itself) into your body. This genetic material instructs your cells to produce a harmless protein that resembles a part of the SARS-CoV-2 virus. Your immune system recognizes this protein as foreign and begins producing antibodies and other immune cells to fight it. This way, if you are exposed to the actual virus in the future, your immune system is prepared to recognize and attack it effectively, preventing you from getting sick or reducing the severity of the illness [\[1\]](). ## Common side effects of the vaccine It is normal to feel some side effects after receiving a COVID-19 vaccine, and these effects are a sign that your body is building protection. Common side effects include [\[1\]](): - Pain, swelling, and redness at the injection site. - Pain and swelling in the lymph nodes (in the same arm where you received the injection). - Fatigue and exhaustion. - Headache. - Muscle and joint pain. - Chills. - Nausea or vomiting. - Fever. - Rash. These side effects are usually mild to moderate and disappear within a few days. If the side effects are bothersome or do not go away, you should contact your healthcare provider or vaccination provider [\[1\]](). ## When should you seek medical help? Although serious side effects are very rare, you should be aware of some symptoms that require immediate medical attention. Call emergency services (9-1-1 in the United States) or go to the nearest hospital if you experience a severe allergic reaction, which usually occurs within minutes to one hour after receiving the vaccine. Signs of a severe allergic reaction include [\[1\]](): - Difficulty breathing. - Swelling of the face and throat. - Fast heartbeat. - Bad rash all over the body. - Dizziness and weakness. You should also seek medical attention immediately if you experience any of the following symptoms after receiving a COVID-19 vaccine, as they may indicate myocarditis or pericarditis, which are rare conditions that occur more commonly in males under 40 years of age [\[1\]](): - Chest pain. - Shortness of breath. - Feeling of a fast-beating, fluttering, or pounding heart. You can learn more about COVID-19 vaccines and how to protect your family and the community from the virus by visiting [COVID-19 Vaccines: Protecting Your Family and Community from the Virus (Arabic)](). ## Important information before vaccination Before receiving the COVID-19 vaccine, it is essential to inform the vaccine provider of all your medical conditions, including [\[1\]](): - Any allergies you have. - If you have ever had myocarditis or pericarditis. - If you currently have a fever. - If you have a bleeding disorder or are taking blood thinners. - If your immune system is weak or you are taking medications that affect the immune system. - If you are pregnant, planning to become pregnant, or breastfeeding. - If you have received another COVID-19 vaccine before. - If you have fainted after receiving a previous vaccine or injection. - If you have had a severe allergic reaction after a previous dose of this vaccine or any of its components. This information helps your healthcare provider ensure that the vaccine is safe and appropriate for you [\[1\]](). ## Medical references - [COVID-19 Vaccine, mRNA Bivalent (Moderna)]() - [COVID-19 Vaccines]() General health education; not a substitute for individualized clinical assessment. Citation URL: https://clinicsjo.com/en/faq/can-covid-19-vaccine-cause-illness#answer