Important: This page is general information, not medical advice. It does not recommend or prescribe any treatment. Always consult your doctor or pharmacist before starting, stopping or changing any medicine.
About Viral Infections
Viruses are very tiny germs. They are made of genetic material (either DNA or RNA) inside of a protein coating. There are a huge number of viruses on earth. Only a small number of them can infect humans. Those viruses can infect our cells, which may cause disease. Some of the diseases that viruses can cause include the common cold, the flu, COVID-19, and HIV.
Viruses can be spread in different ways:
- Through droplets and particles that are breathed out by someone who has the infection. You might breathe in the droplets or particles, or they could land on your mouth, nose, or eyes.
- By touching surfaces or objects that have the virus on them and then touching your mouth, nose, or eyes.
- From the pregnant parent to the baby during pregnancy.
- Through contaminated food or water.
- By being bitten by an infected insect or animal.
- Through sexual contact (usually vaginal, anal and oral sex) with someone who has the infection.
Viruses are like hijackers. They invade living, normal cells. They then use those cells to multiply (make copies of themselves). This process is also called replication. The process can kill, damage, or change the infected cells. Sometimes this can make you sick. The symptoms can range from mild to very severe. Other times, your immune system may be able to fight it off and you may not have any symptoms.
Each different virus usually only infects one type of cell in your body. For example, hepatitis viruses affect the cells in the liver. HIV infects a certain type of immune system cell.
For most viral infections, treatments can only help with symptoms while you wait for your immune system to fight off the virus. There are antiviral medicines to treat some viral infections. Antibiotics do not work for viral infections.
Vaccines can help prevent you from getting many viral diseases. You may be able to prevent some viral infections by:
- Proper hand washing.
- Paying attention to food safety.
- Cleaning surfaces that may be infected with germs.
- Avoiding contact with wild animals.
- Preventing insect bites by using insect repellent when you go outdoors. If you travel to an area that has a high risk of diseases from insect bites, also wear long pants, shirts, and socks.
- Practicing safe sex (using a condom every time you have anal, vaginal, or oral sex).
- Avoiding close contact with people who are sick.
It sits within Infections and Immune System.
The lead U.S. institute for this subject is the National Institute of Allergy and Infectious Diseases.
When to speak to someone. Reading about a topic cannot tell you whether it applies to you. Speak to a doctor or pharmacist if symptoms are severe, sudden, getting worse, or simply not going away — and seek emergency care immediately for chest pain, breathing difficulty, sudden weakness or confusion, or a serious allergic reaction.
Research on Viral Infections
28,105 studies areregistered for this condition on ClinicalTrials.gov, the U.S. National Library of Medicine's public registry. A selection is below — the links go straight to the registry entry, not to a summary of ours.
What a registered study does and does not mean. Registration means a study exists and has been declared publicly. It says nothing about whether the treatment being tested works, is safe, or is available to you. Many studies find no benefit — that is what research is for. Never seek out an experimental treatment on the strength of a registry entry alone.
Research currently under way
- Inotuzumab Ozogamicin in Treating Younger Patients With B-Lymphoblastic Lymphoma or Relapsed or Refractory CD22 Positive B Acute Lymphoblastic LeukemiaChildren's Oncology Group
- A Study to Learn About the Study Medicine Ibuzatrelvir in Adults With COVID-19 Who Are Severely ImmunocompromisedPfizer
- Long-term Follow-up of Long-acting Cabotegravir (CAB LA) for PrEP (Pre-exposure Prophylaxis) in Participants at Risk of Acquiring HIV (Human Immunodeficiency Virus)ViiV Healthcare
- Study of GS-4321 in Healthy Participants and Participants With Chronic Hepatitis Delta VirusGilead Sciences
- Screening for LID Clinical Studies Unit Healthy Volunteer ProtocolsNational Institute of Allergy and Infectious Diseases (NIAID)
- Long-term Follow up Local Registry Study of Kymriah in South KoreaNovartis Pharmaceuticals
Research already completed
- Natural History of Systemic and Nasal Mucosal Immunity to Influenza and SARS-CoV-2 in Adults After VaccinationNational Institute of Allergy and Infectious Diseases (NIAID)
- Increasing PrEP Use in High-Risk Social Networks of African-American MSM in Underserved Low-Risk CitiesMedical College of Wisconsin
- Recombinant Influenza Vaccine Versus Standard Egg-Based Inactivated Influenza Vaccine in Adults 18-64 YearsCenters for Disease Control and Prevention
- Phase I/II Clinical Trial of Influenza Vaccine (Split Virion), Inactivated (High Dose)Sinovac Biotech Co., Ltd
- Herpesviruses Reactivation In Hiv-Infected Women Initiating ART (HERA)National Institute of Allergy and Infectious Diseases (NIAID)
- Effects of Immulina TM Supplements With PASC PatientsUniversity of Mississippi Medical Center
Study data from ClinicalTrials.gov, a service of the U.S. National Library of Medicine. Retrieved 2026-07-30. Registry entries are supplied by study sponsors and investigators; ClinicalTrials.gov does not verify their scientific validity. PocketsInfo is not affiliated with, and not endorsed by, the NLM or the NIH.
Where to read more
Rather than paraphrase, we point you to the primary sources. Every link below is to a government health agency, a national institute or a recognised medical body — grouped by what you are trying to find out.
Start Here
- Bacterial vs. Viral Infections: How Do They Differ?Mayo Foundation for Medical Education and Research
- Overview of Viral InfectionsMerck & Co., Inc.
Diagnosis and Tests
- Immunoglobulins Blood TestNational Library of Medicine
- PCR TestsNational Library of Medicine
- Rapid TestsNational Library of Medicine
- Respiratory Pathogens PanelNational Library of Medicine
Prevention and Risk Factors
- Germs and Hygiene: MedlinePlus Health TopicNational Library of Medicine
- Infection Control: MedlinePlus Health TopicNational Library of Medicine
Related Issues
- Infection Control BasicsCenters for Disease Control and Prevention
- Viruses that Can Lead to CancerAmerican Cancer Society
Genetics
- Genomics and VirologyNational Human Genome Research Institute
Clinical Trials
- ClinicalTrials.gov: Adenoviridae InfectionsNational Institutes of Health
- ClinicalTrials.gov: Coxsackievirus InfectionsNational Institutes of Health
- ClinicalTrials.gov: EnterovirusNational Institutes of Health
- ClinicalTrials.gov: Hand, Foot and Mouth DiseaseNational Institutes of Health
- ClinicalTrials.gov: Virus DiseasesNational Institutes of Health
Medical subject headings
Clinicians and researchers index this subject under Virus Diseases. These are the terms to use when searching medical literature.
This page is built from the MedlinePlus health topic record for Viral Infections, a service of the U.S. National Library of Medicine (NLM), National Institutes of Health. Information is from MedlinePlus.gov. PocketsInfo is not affiliated with, and is not endorsed by, the NLM or the NIH. Retrieved 30 July 2026.