COVID-19 Vaccine: Types, Safety & Side Effects

How Do COVID-19 Vaccines Work?

COVID-19 vaccines work by teaching your immune system to recognize and fight the SARS-CoV-2 virus without causing infection. They trigger the production of antibodies and T-cells that provide protection if you are exposed to the real virus, significantly reducing your risk of severe illness.

Vaccines have been one of medicine's greatest achievements, preventing millions of deaths from infectious diseases worldwide. COVID-19 vaccines were developed using decades of scientific research and have undergone rigorous clinical trials to ensure they are both safe and effective. Understanding how these vaccines work can help you make informed decisions about your health.

When the SARS-CoV-2 virus enters your body, it uses its distinctive spike protein to attach to and enter your cells. The virus then hijacks your cell's machinery to make copies of itself, spreading the infection throughout your body. COVID-19 vaccines target this spike protein, training your immune system to recognize it as a threat and mount a defense before the virus can cause serious harm.

Your immune system responds to vaccination by producing antibodies, which are proteins that can recognize and neutralize the virus if you encounter it later. Vaccines also stimulate the production of T-cells, which can destroy infected cells and coordinate the overall immune response. This combination of antibodies and T-cells provides robust protection against COVID-19. Importantly, your immune system also develops memory cells that can quickly ramp up this protective response if you are exposed to the virus in the future.

mRNA Vaccines

Messenger RNA (mRNA) vaccines, such as those made by Pfizer-BioNTech (Comirnaty) and Moderna (Spikevax), represent a breakthrough in vaccine technology. These vaccines deliver genetic instructions in the form of mRNA that tell your cells how to make a harmless piece of the spike protein. Your cells follow these instructions, produce the spike protein, and display it on their surface. This triggers your immune system to recognize the spike protein as foreign and mount a protective response.

The mRNA from the vaccine is quickly broken down by your body, typically within a few days. It never enters the nucleus of your cells where your DNA is stored, so it cannot alter your genetic material. This technology has been studied for decades and has proven to be extremely safe and effective. mRNA vaccines can also be quickly updated to target new variants, making them valuable tools in the ongoing fight against COVID-19.

Viral Vector Vaccines

Viral vector vaccines, such as the Johnson & Johnson (Janssen) vaccine and AstraZeneca vaccine, use a modified version of a different virus (the vector) to deliver instructions to your cells. The vector virus has been engineered so it cannot replicate or cause disease. Once inside your cells, the vector provides instructions for making the spike protein, which then triggers an immune response similar to that produced by mRNA vaccines.

This technology has been used for decades in other vaccines and gene therapies. The modified virus used as a vector is completely safe and cannot cause COVID-19 or any other illness. These vaccines have proven effective at preventing severe COVID-19 illness and have been administered to hundreds of millions of people worldwide.

Protein Subunit Vaccines

Protein subunit vaccines, such as the Novavax vaccine, take a more traditional approach. They contain harmless pieces of the spike protein itself, rather than genetic instructions for making it. These protein fragments are combined with an adjuvant, a substance that enhances the immune response, to stimulate strong and lasting protection.

This technology has been used successfully for decades in vaccines against hepatitis B, pertussis, and other diseases. Protein subunit vaccines may be a good option for people who prefer a more traditional vaccine technology or who have had reactions to mRNA or viral vector vaccines.

What Types of COVID-19 Vaccines Are Available?

Several types of COVID-19 vaccines have been authorized for use globally, including mRNA vaccines (Pfizer-BioNTech, Moderna), viral vector vaccines (Johnson & Johnson, AstraZeneca), and protein subunit vaccines (Novavax). Each type uses different technology but all are effective at preventing severe illness.

The development of COVID-19 vaccines represents one of the fastest and most successful vaccine development efforts in history. Multiple pharmaceutical companies and research institutions collaborated with governments and regulatory agencies worldwide to bring safe and effective vaccines to market in record time. This was possible because of decades of prior research on coronavirus biology and vaccine technology, combined with unprecedented levels of funding and parallel rather than sequential development phases.

Different countries have authorized different vaccines based on their regulatory processes, supply agreements, and population needs. Despite the variety of vaccines available, all authorized COVID-19 vaccines have demonstrated strong efficacy against severe disease, hospitalization, and death. The World Health Organization has granted Emergency Use Listing to several vaccines, and regulatory agencies in countries around the world continue to monitor vaccine safety through robust surveillance systems.

It is important to note that efficacy numbers from clinical trials may not be directly comparable between vaccines, as studies were conducted at different times, in different populations, and against different circulating variants. Real-world effectiveness studies consistently show that all authorized vaccines provide strong protection against severe disease and death, which is the most important outcome.

Who Should Get a COVID-19 Vaccine?

COVID-19 vaccination is recommended for most people aged 6 months and older. It is especially important for older adults, people with underlying health conditions, pregnant individuals, and healthcare workers who face higher risks from COVID-19 infection.

The decision to get vaccinated should be made in consultation with your healthcare provider, particularly if you have specific health concerns or a history of severe allergic reactions. However, for the vast majority of people, the benefits of COVID-19 vaccination far outweigh the risks. Vaccination protects not only yourself but also helps reduce transmission to vulnerable individuals who may not be able to get vaccinated or who may have weaker immune responses to vaccination.

COVID-19 can affect anyone, but certain groups face significantly higher risks of severe illness, hospitalization, and death. Understanding these risk factors can help you and your healthcare provider make informed decisions about vaccination timing and the importance of staying up to date with booster doses.

High-Risk Groups

Older adults, particularly those aged 65 and above, are at substantially higher risk of severe COVID-19 outcomes. The immune system naturally weakens with age, making it harder to fight off infections and potentially reducing the duration of vaccine-induced protection. For this reason, older adults are often prioritized for initial vaccination and booster doses.

People with certain underlying health conditions also face increased risks from COVID-19. These conditions include chronic lung disease (such as COPD or asthma), heart disease, diabetes, chronic kidney disease, liver disease, and conditions that weaken the immune system (such as cancer treatment, organ transplant, or HIV). Obesity is also associated with higher risk of severe COVID-19. If you have any of these conditions, vaccination is particularly important for your protection.

• Adults 65 years and older: At highest risk for severe illness and death from COVID-19
• People with chronic conditions: Including diabetes, heart disease, lung disease, kidney disease, and liver disease
• Immunocompromised individuals: May need additional vaccine doses for adequate protection
• Pregnant individuals: Vaccination is safe and protects both mother and baby
• Healthcare workers: Higher exposure risk and potential to transmit to vulnerable patients
• Long-term care residents: Living in congregate settings with vulnerable populations

Pregnancy and Vaccination

Pregnant individuals are at increased risk of severe COVID-19 illness, including ICU admission and death. COVID-19 during pregnancy is also associated with higher rates of preterm birth and other complications. Extensive safety data from millions of pregnant people who have received COVID-19 vaccines shows that vaccination is safe during pregnancy and does not increase the risk of miscarriage, stillbirth, or birth defects.

Furthermore, antibodies produced after vaccination can cross the placenta and provide some protection to newborns in their first months of life, before they are old enough to be vaccinated themselves. Major medical organizations including the World Health Organization, the American College of Obstetricians and Gynecologists, and the Royal College of Obstetricians and Gynaecologists all recommend COVID-19 vaccination during pregnancy.

Children and Vaccination

While children generally have milder COVID-19 illness than adults, they can still become seriously ill, develop long COVID, or transmit the virus to more vulnerable family members and community members. COVID-19 vaccines have been authorized for children as young as 6 months old, with dosing adjusted based on age.

Clinical trials in children have demonstrated that COVID-19 vaccines are safe and effective at preventing symptomatic infection and severe illness. The most common side effects in children are similar to those in adults: injection site pain, fatigue, headache, and fever. These are typically mild and resolve within a few days.

What Are the Common Side Effects of COVID-19 Vaccines?

Common side effects include pain at the injection site, fatigue, headache, muscle pain, chills, and fever. These typically appear within 1-2 days after vaccination and resolve within a few days. Side effects are signs that your immune system is building protection and are not cause for concern.

Like all vaccines and medications, COVID-19 vaccines can cause side effects. Most side effects are mild to moderate and are a normal sign that your body is building protection against the virus. Understanding what to expect can help you plan accordingly and reduce any anxiety about getting vaccinated.

The most commonly reported side effects occur at the injection site on your upper arm. Pain, redness, and swelling where the shot was given are experienced by the majority of vaccine recipients. These local reactions are caused by your immune system's initial response to the vaccine and typically resolve within a day or two. Applying a clean, cool, wet washcloth to the area and using or exercising your arm can help reduce discomfort.

Systemic side effects, which affect your whole body, are also common but usually mild. These include fatigue, headache, muscle pain, chills, fever, and nausea. These symptoms are more common after the second dose of a two-dose series and may be more pronounced in younger people, who tend to have stronger immune responses. Most people can continue their normal activities, though some may need to rest for a day or so.

Managing Common Side Effects

There are several steps you can take to manage common side effects. For injection site pain, continue to move your arm throughout the day and apply a cool compress if needed. For systemic symptoms like fever and body aches, over-the-counter pain relievers such as acetaminophen (paracetamol) or ibuprofen can help. Stay hydrated and get plenty of rest.

It is important to note that taking pain relievers before vaccination to try to prevent side effects is not recommended, as this may reduce your immune response to the vaccine. However, taking them after vaccination to manage symptoms that do occur is perfectly fine and will not affect the vaccine's effectiveness.

Rare Side Effects

Serious side effects from COVID-19 vaccines are rare. Anaphylaxis, a severe allergic reaction, occurs in approximately 2-5 cases per million doses administered. This is why vaccination sites ask you to wait 15-30 minutes after your shot for observation. Anaphylaxis is treatable and vaccination staff are trained to respond to these events.

Myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the lining around the heart) have been reported after mRNA COVID-19 vaccination, particularly in adolescent and young adult males after their second dose. These cases are rare, occurring in approximately 1-5 per 100,000 vaccinated males in this age group. Most cases are mild, respond well to treatment, and resolve quickly. The risk of myocarditis from COVID-19 infection itself is substantially higher than from vaccination.

Thrombosis with thrombocytopenia syndrome (TTS), a rare condition involving blood clots and low platelet counts, has been associated with viral vector vaccines (particularly Johnson & Johnson and AstraZeneca). This very rare condition occurs in approximately 1-2 per million doses and is most commonly seen in younger women. Many countries have adjusted their recommendations for these vaccines based on this risk.

Are COVID-19 Vaccines Safe?

Yes, COVID-19 vaccines are safe. They have been rigorously tested in clinical trials involving tens of thousands of participants and continue to be monitored through extensive global safety surveillance systems. The benefits of vaccination significantly outweigh the small risks of side effects.

Vaccine safety has been a top priority throughout the development, authorization, and deployment of COVID-19 vaccines. Despite the unprecedented speed of development, no safety steps were skipped. The rapid timeline was achieved through parallel processing of development phases, massive funding that eliminated financial barriers, and the ability to quickly enroll trial participants during an active pandemic.

Before any COVID-19 vaccine was authorized for use, it underwent rigorous clinical trials involving tens of thousands of diverse participants. These trials tested for both efficacy (how well the vaccine prevents disease) and safety (what side effects occur and how often). Independent safety monitoring boards reviewed data throughout the trials to ensure participant safety.

Regulatory agencies around the world, including the U.S. Food and Drug Administration (FDA), European Medicines Agency (EMA), and many others, conducted thorough reviews of all clinical trial data before granting emergency use authorization or full approval. These reviews examined manufacturing processes, quality control, and detailed safety and efficacy data.

Ongoing Safety Monitoring

Safety monitoring did not stop once vaccines were authorized. Multiple surveillance systems track vaccine safety in real-time as vaccines are administered to millions of people. In the United States, these include the Vaccine Adverse Event Reporting System (VAERS), the Vaccine Safety Datalink (VSD), and the V-safe smartphone-based health checker. Similar systems exist in other countries and internationally through the World Health Organization.

These surveillance systems have successfully identified rare side effects that were too uncommon to detect in clinical trials, such as myocarditis and TTS. When potential safety signals are detected, they are thoroughly investigated by teams of experts, and recommendations are updated accordingly. This demonstrates that the safety monitoring systems work as intended.

After years of use and billions of doses administered worldwide, COVID-19 vaccines have an excellent safety record. The vast majority of reported adverse events are minor and temporary. Serious adverse events are very rare, and for most people, the risk of serious complications from COVID-19 infection is far greater than the risk of serious complications from vaccination.

Do I Need a COVID-19 Booster Shot?

Yes, booster shots are recommended to maintain strong protection against COVID-19, especially as immunity decreases over time and new variants emerge. Updated boosters targeting current circulating variants provide the best protection. High-risk groups are particularly encouraged to stay up to date with boosters.

Like many vaccines, COVID-19 vaccines provide protection that can decrease over time. Studies have shown that antibody levels begin to decline several months after vaccination, and this decline is associated with reduced protection against symptomatic infection, though protection against severe disease tends to remain stronger for longer.

Additionally, the SARS-CoV-2 virus continues to evolve, and new variants may partially evade immunity from previous vaccination or infection. Updated booster vaccines that target current circulating variants can provide better protection than boosters based on the original virus strain alone.

Health authorities including the World Health Organization, U.S. Centers for Disease Control and Prevention, and European Centre for Disease Prevention and Control recommend booster doses for most adults, with particular emphasis on those at higher risk of severe disease. The specific recommendations for timing and number of boosters may vary by country and continue to evolve as new data emerges and new variants circulate.

Who Should Get Boosters?

Booster recommendations generally prioritize those at highest risk of severe COVID-19. Older adults, immunocompromised individuals, and people with underlying health conditions are often advised to receive boosters at more frequent intervals than healthy younger adults. Healthcare workers and others with high exposure risk may also be prioritized.

For most healthy adults, annual booster doses (similar to annual influenza vaccination) may become the standard recommendation. However, specific guidance continues to evolve based on the epidemiological situation, circulating variants, and available vaccine formulations. Consult your healthcare provider or check with your local public health authority for the most current recommendations in your area.

• Adults 65 and older: Strongly recommended to receive updated boosters
• Immunocompromised individuals: May need additional doses and more frequent boosters
• People with chronic conditions: Recommended to stay up to date with boosters
• Healthcare workers: Recommended for personal protection and to reduce transmission to patients
• General adult population: Annual booster doses are increasingly recommended

How Can I Get a COVID-19 Vaccine?

COVID-19 vaccines are available through healthcare providers, pharmacies, community health centers, and public health clinics in most countries. Many locations offer walk-in appointments, and vaccines are often provided free of charge. Contact your healthcare provider or local public health department to find vaccination sites near you.

Getting vaccinated against COVID-19 is easier than ever in most parts of the world. As initial supply constraints have been resolved, vaccines have become widely available through multiple channels. Whether you are seeking your first vaccination or a booster dose, there are likely several convenient options in your area.

Many countries have established online tools and hotlines to help people find vaccination appointments. Pharmacies in many regions can administer COVID-19 vaccines without a prescription or appointment. Community health centers often serve underserved populations and may offer vaccines during extended hours or at community events.

Preparing for Your Vaccination Appointment

When you go to get vaccinated, there are a few things you can do to prepare. Wear a short-sleeved shirt or one with sleeves that can be easily rolled up, as the injection is given in the upper arm. Bring any identification and insurance information that may be required, though many vaccination sites do not require insurance to receive free COVID-19 vaccines.

If you are receiving a booster dose, bring your vaccination record card if you have one, so it can be updated with your new dose. Inform the vaccination staff of any previous reactions to vaccines or known allergies. Be prepared to wait 15-30 minutes after your vaccination for observation to ensure you do not have an immediate allergic reaction.

Common Myths About COVID-19 Vaccines

Many misconceptions about COVID-19 vaccines circulate online. Scientific evidence clearly shows that vaccines do not cause COVID-19 infection, do not alter your DNA, do not contain microchips, and do not cause infertility. Understanding the facts helps you make informed decisions about your health.

Misinformation about COVID-19 vaccines has spread widely, particularly on social media. This misinformation can cause confusion and fear, potentially leading people to delay or refuse vaccination that could protect them from serious illness. Understanding the facts behind common myths is important for making informed health decisions.

Myth: COVID-19 vaccines can give you COVID-19

This is false. None of the authorized COVID-19 vaccines contain the live SARS-CoV-2 virus that causes COVID-19. mRNA vaccines contain only genetic instructions for making the spike protein, viral vector vaccines use a modified virus that cannot replicate, and protein subunit vaccines contain only protein fragments. You cannot get COVID-19 from any of these vaccines.

If you develop COVID-19 symptoms shortly after vaccination, it means you were likely exposed to the virus before or around the time of vaccination, before your body had time to build protection. This is why continuing protective measures like masking in high-risk situations is recommended until you are fully vaccinated and your immunity has had time to develop.

Myth: COVID-19 vaccines alter your DNA

This is false. mRNA from vaccines never enters the nucleus of your cells, where your DNA is stored. The mRNA provides instructions to your cells' protein-making machinery, which is located outside the nucleus, and is then quickly broken down. Viral vector vaccines also do not alter your DNA. Your genetic material remains unchanged after vaccination.

Myth: COVID-19 vaccines cause infertility

This is false. There is no scientific evidence that COVID-19 vaccines affect fertility in men or women. This myth appears to have originated from a misunderstanding about the spike protein and a protein involved in placenta development. These proteins are actually quite different, and the immune response to the spike protein does not cross-react with reproductive proteins.

Clinical trials included pregnant participants, and extensive post-authorization data from hundreds of thousands of pregnant people who received COVID-19 vaccines shows no increased risk of pregnancy complications or birth defects. Major fertility organizations, including the American Society for Reproductive Medicine, recommend COVID-19 vaccination for people who are trying to become pregnant.

Myth: Natural immunity is better than vaccine immunity

While infection with COVID-19 does provide some immunity, this protection is variable and unpredictable. Some people develop strong immunity after infection while others develop little protection. Getting COVID-19 to build natural immunity also carries significant risks of severe illness, long COVID, hospitalization, and death.

Research shows that vaccination after previous infection (hybrid immunity) provides the strongest and most durable protection. Health authorities recommend vaccination even for people who have previously had COVID-19, as vaccination provides a more reliable and safer way to build protective immunity.

Frequently Asked Questions