The immune system protects us against pathogens, which are microbes that cause infection. Vaccines “teach” the immune system to recognize and eliminate certain microbes. That way, your body is prepared if you’re ever exposed.

Vaccinations are an important form of primary prevention. That means they can protect people from getting sick. Vaccinations have allowed us to control diseases that once threatened many lives, such as:

It’s important that as many people as possible get vaccinated. Vaccinations don’t just protect individuals. When enough people are vaccinated, it helps protect society.

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Illustration by Wenzdai Figueroa

Vaccines are very important for infants. But not all vaccines are given immediately after birth. Each vaccine is given on a timeline, and some require multiple doses.

Childhood vaccination schedule

The Centers for Disease Control and Prevention (CDC) sets a recommended vaccine schedule for both children and adults, which is shown in the table below.

If you didn’t receive some of your childhood vaccines, it’s still possible to get them as an adult. However, depending on the vaccine, the dosing schedule may be different. You can ask your doctor what to expect.

Name of VaccineAgeHow many shots?
Hepatitis BBirthA second at 1–2 months, a third at 6–18 months
Rotavirus (RV)2 monthsA second at 4 months, a third at 6 months
Diphtheria, tetanus, and whooping cough (DTaP)2 monthsA second at 4 months, a third at 6 months, a fourth at 15–18 months, a fifth at 4 to 6 years, and then every 10 years
Haemophilus influenzae type b (Hib)2 monthsA second at 4 months, a third at 6 months, a fourth at 12–15 months
Pneumococcal conjugate vaccine PCV132 monthsA second at 4 months, a third at 6 months, a fourth at 12-15 months
Inactivated Polio Vaccine (IPV)2 monthsA second at 4 months, a third at 6–18 months, a fourth at 4-6 years
Influenza6 monthsRepeat yearly
Measles, mumps, and rubella (MMR)12–15 monthsA second at 4–6 years
Varicella12–15 monthsA second at 4–6 years
Hepatitis A12–23 monthsA second at 6 months after the first
COVID-19 6 months -17 yearsModerna:
2 doses 4-8 weeks apart and then a booster dose after 2 months.
Pfizer and Novavax (12 years and older only):
2 doses 3-8 weeks apart and then a booster dose after 2 months.

Human papillomavirus (HPV)11–12 years old2-shot series 6 months apart
Meningococcal conjugate (MenACWY) 11–12 years oldBooster at 16 years old
Human papillomavirus (HPV)11-12 years oldA second 6-12 months after the first
Herpes zoster (Shringrix)50 years oldA second 6 months after the first
Pneumococcal 65+ years old1 dose PCV15 followed by PPSV23 or 1 dose PCV20

Many vaccines are given in a group or series. It may seem like your child is getting a lot of vaccines all at once.

But according to the CDC, there’s no data that supports spacing out childhood vaccines. In fact, delaying a child’s vaccinations can do more harm than good, leaving them vulnerable to pathogens that can cause serious illness or complications.

In addition to regular childhood vaccinations, adults should receive:

Your doctor may also suggest you receive additional vaccines or boosters based on your sexual orientation, health history, personal hobbies, and other factors. These possible vaccines include:

  • Bacterial meningococcal disease: This is a bacterial illness that causes inflammation of the layer of tissue surrounding your brain and spinal cord. While the meningococcal ACWY vaccine is recommended for all adolescents, the meningococcal B vaccine is also recommended for individuals with certain immune conditions.
  • Yellow fever: This is a serious and potentially deadly viral disease that’s spread by mosquitoes. The CDC recommends anyone nine months and older be vaccinated against yellow fever if they plan to travel or live in areas of the world where yellow fever is present.
  • Typhoid fever: This is a potentially dangerous infectious disease. The CDC recommends adults and children be vaccinated against typhoid before international travel to places where typhoid fever is common.

Other vaccines you may need if you’re planning to travel are outlined by the CDC in its Travel vaccine summary table.

A healthy immune system defends against invaders. The immune system is composed of several types of cells. These cells defend against and remove harmful pathogens. However, they first have to recognize that an invader is dangerous.

When the immune system encounters an antigen, it starts an immune response. Proteins, toxins, and nucleic acids from pathogens are all examples of potential antigens.

In response, the immune system makes antibodies, which are proteins that bind to specific antigens and neutralize them. It also leads to the expansion of antigen-specific immune cells called cytotoxic T cells, which find and destroy cells that have been infected with a pathogen.

Vaccination, also known as immunization, teaches the body to recognize new diseases by stimulating the body to make antigens for pathogens, priming the immune system to remember them. This allows for a faster response to the actual disease in the future, should you be exposed.

Vaccines work by exposing you to a safe version of a disease. This can take the form of:

  • a protein or sugar from a pathogen
  • a dead or inactivated form of a pathogen
  • a modified toxin (toxoid) from a pathogen
  • a live but weakened form pathogen

Vaccines are usually given by injection. Also, some vaccines require a booster dose. Boosters help to reinforce your defenses against illness.

When it comes to vaccination, these benefits are important to consider:

  • Vaccines help prevent dangerous diseases that have killed and can sicken or kill many people.
  • Researchers thoroughly investigate each vaccine before presenting the data to the Food and Drug Administration (FDA). The FDA can approve or deny the vaccine. The overwhelming majority of research shows that vaccines are safe.
  • Vaccines protect people around you, especially people who are not well enough to be vaccinated. This occurs through herd immunity. Widespread vaccinations make it less likely that a susceptible person will come into contact with someone who has a particular disease.
  • Some vaccines, such as the human papillomavirus (HPV) vaccine and hepatitis B vaccine, can prevent infections that can cause cancer.
  • Preventing illness from vaccine-preventable diseases can save both time and money. For example, it can reduce the number of sick days you need to take from work or school and can help you avoid unnecessary medical bills.
  • Sometimes, vaccination can eliminate a disease entirely, such as smallpox. Additionally, polio has been almost been eradicated. According to the World Health Organization (WHO), wild poliovirus only impacted two countries in 2022 – Afghanistan and Pakistan.

Vaccines are considered to be safe. They’re rigorously tested and go through many rounds of study, examination, and research before they’re used with the general public. The CDC provides information about how vaccine safety is ensured.

Mild side effects

It is possible to experience some side effects, but these are usually mild. Common side effects may include:

A 2021 study on the Pfizer–BioNTech COVID-19 vaccine in a population found that 89.8% of people experienced some pain at the injection site, 45.6% experienced headaches, 37.1% experienced muscle pain, and 33.9% experienced chills.

Most mild vaccine side effects go away on their own within a few days. Some side effects, such as pain and fever, can be alleviated through the use of over-the-counter medications like acetaminophen (Tylenol) or ibuprofen (Advil, Motrin)

Allergy and anaphylaxis

it is possible to experience an allergic reaction to a vaccine, though the CDC reports this is uncommon. Common symptoms may include hives at the injection site and angioedema.

In even rare cases, you could experience a serious allergic reaction called anaphylaxis. Research shows the overall anaphylaxis rate for all vaccines is only 1.31 per 1 million vaccine doses.


Anaphylaxis is a severe reaction to a trigger, such as an allergy, and is potentially life threatening.

Symptoms can come on quickly and include:

  • feeling faint or lightheaded
  • difficulty breathing or wheezing
  • rapid heartbeat
  • confusion
  • anxiety
  • clammy skin
  • collapsing or losing consciousness
  • hives
  • swelling
  • stomach pain, nausea, or vomiting

If you or someone around you develops these symptoms, you should:

  1. Check to see whether they have an epinephrine pen. If they do, read and follow the instructions to dispense the medication.
  2. Dial 911 (or a local emergency number).
  3. Lay them down. If they have vomited, lay them on their side.
  4. Stay with them until emergency services arrive.

It is possible for someone to need more than one injection with an epinephrine pen. If symptoms do not begin to clear after 5 minutes, give a second injection if one is available.

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Another example is myocarditis, which is an inflammation of the heart muscle and a rare side effect of COVID-19 mRNA vaccines.

However, a 2021 study found that the risk of myocarditis is actually higher in people who contract COVID-19 than it is in those who get an mRNA vaccine for COVID-19.

Because most of the possible side effects are rare or relatively mild, the greatest risk for most individuals is choosing not to get a vaccine.

Not getting vaccinated can lead to infection, more severe illness, and transmission to others who may be vulnerable. It could also cause lasting complications or even be deadly.

You may have more questions about the safety of vaccines. This guide to vaccine safety can help.

Generally speaking, vaccines are highly effective. However, no vaccine is 100 percent effective. The effectiveness rate for vaccines differs from one vaccine to the next.

For example, flu vaccines effectively lower the risk of infection by 40-60% in people who get the shot. That may sound low, but keep in mind the flu vaccine is designed to match the strain of the flu scientists expect to be most abundant in the coming flu season.

If they’re wrong, the vaccine may be less effective. If they’re right, the rate of protection may be higher.

The measles vaccine, on the other hand, is 97% effective when used as recommended. Indeed, most childhood vaccines are 85-95% effective if administered properly, according to the WHO.

In recent years, vaccine opponents have challenged their safety and effectiveness. However, their arguments have generally been flawed.

For instance, there’s no good evidence that vaccination can cause Autism Spectrum Disorder (ASD). On the other hand, there is plenty of evidence of vaccine effectiveness. For example, vaccines prevent 3.5-5 million deaths annually, according to the WHO.

There are some other cases in which someone might not get vaccinated:

  • Weakened immune system: In this case, you should not get live vaccines such as the MMR vaccine or the chickenpox (varicella) vaccine. However, other types of vaccines would still be generally safe.
  • Previous allergic reaction: If you’ve had an allergic reaction to a vaccine before or you know you are allergic to an ingredient in the vaccine, you will need to avoid being immunized. Read more about which people should avoid certain vaccines and why.
  • Lack of awareness: According to the CDC, only 50.2% of American adults got the annual flu shot during the flu season of 2020 to 2021. A 2017 survey study of adults in the United States found that only 62.3% of respondents knew that there was a recommendation for the flu vaccine.
  • Vaccine inequity: People from historically marginalized groups may have less access to quality healthcare, including to vaccinations, than people who are white.

New vaccines are being developed all of the time. The COVID-19 vaccines are a relatively recent example. These vaccines came about through a combination of building on previous research, an influx of private and public funding, and scientific collaboration. Learn more about the types of Covid vaccines available.

Additionally, a new vaccine has been developed for malaria. Malaria is a febrile illness that’s caused by a parasite carried by mosquitoes. According to the WHO, there were a total of 247 million malaria cases and 619,000 malaria deaths worldwide in 2021.

The vaccine, called RTS,S/AS01, contains recombinant proteins from the malaria parasite. Based on the results of a pilot program, the World Health Organization (WHO) recommended the use of this vaccine in children that live in areas with high malaria transmission.

Another intense area of research is in finding a vaccine for HIV. The high diversity of HIV and its high mutation rate are just two of the hurdles that have made this endeavor challenging.

Many trials of potential HIV vaccines have been performed or are in progress. Some of the newest trials involve the use of mRNA vaccine approaches similar to those used for the COVID-19 vaccines.

Most recently, in 2022, emergency authorization was granted for Jynneos, a vaccine against Mpox (formerly known as monkeypox).

Vaccines introduce your immune system to a pathogen so that you have protection from it, should you be exposed. Several types of vaccines are currently used to accomplish this:

  • Live virus vaccines: These use a weakened (attenuated) version of a pathogen.
  • Killed (inactivated) vaccines: These are made from a pathogen that’s not living.
  • Toxoid vaccines: These come from a harmful toxin that’s made by a pathogen. Toxoid vaccines don’t make you immune to the germ, but instead, they make you immune to the harmful effects of the toxin of a germ.
  • Subunit, recombinant, polysaccharide, and conjugate vaccines: These take a structural component from a virus or bacterium that can train your immune system to attack this part of the germ.
  • mRNA vaccines: These use a piece of mRNA to teach your cells to produce a protein from a pathogen that your immune system can then generate a response to
  • Viral vector vaccines: These use a modified, non-replicating virus to show your cells how to make a protein from a pathogen that your immune system can then make a response to

In addition to the actual antigen, other ingredients are used to keep vaccines safe during production, storage, and transportation. These ingredients may also help the vaccine work more effectively once it’s administered and represent a very small portion of the vaccine. They may include:

  • Suspending fluid: Sterile water, saline, or other fluids keep the vaccine safe during production, storage, and use.
  • Adjuvants or enhancers: These ingredients help make the vaccine more effective once it’s injected. Examples include aluminum gels or salts.
  • Preservatives and stabilizers: Many vaccines are made months, even years before they’re used. These ingredients help prevent the antigen from breaking down and becoming ineffective. Examples of a stabilizer are monosodium glutamate (MSG) and thimerosal.
  • Antibiotics: Very small amounts of a bacteria-fighting drug may be added to vaccines to prevent the growth of bacteria during vaccine production and storage.

Each of these ingredients is studied rigorously for safety and efficiency. See how these ingredients work together in the flu vaccine.


One vaccine ingredient that has been surrounded by a bit of controversy is thimerosal, a mercury-based preservative that is currently used in the adult multi-dose flu vaccine. The ingredient has not been put into any childhood vaccines since 2001.

However, its more widespread use in the past has contributed to the false belief in a link between vaccines and autism spectrum disorder (ASD).

When you’re pregnant, vaccines don’t just protect you. They provide immunity to your growing baby. During these nine months, you and your baby need protection against serious diseases, and vaccines are a vital part of that.

The CDC recommends that people assigned female at birth planning to become pregnant receive an MMR vaccine before conceiving. These diseases, particularly rubella, can lead to serious issues, including miscarriage and birth defects.

Additionally, the CDC recommends people assigned female at birth also have certain vaccinations during their pregnancy. These include vaccines for whooping cough (Tdap), flu, and COVID-19.

After pregnancy, people assigned female at birth can receive vaccines, even while breastfeeding or chestfeeding. Post-pregnancy vaccinations also help protect your infant. If you’re immune to a virus or bacterium, you’re less likely to share it with your child.

If you aren’t properly vaccinated, you and your infant could get sick. Read why that’s a serious problem with the flu.

Most health insurance plans cover vaccinations at little or no out-of-pocket cost to you. If you do not have insurance or your insurance does not cover vaccines, you can look for low- and no-cost alternatives.

These include:

  • Community health organizations: Many organizations provide vaccine clinics for infants and children at a greatly reduced rate.
  • Vaccines for Children Program:This no-cost program provides recommended vaccines to children who do not have health insurance, are underinsured, are Medicaid-eligible, can’t afford the shots, or are Native Americans or Alaska Natives.
  • State health departments: These community-based offices can provide basic health services, including vaccines, on a low cost basis.

The CDC provides a routinely-updated list of vaccine costs so that consumers may have an idea of the out-of-pocket cost of a vaccine. If you do not have insurance and don’t qualify for any of these cost-reduction programs, this list may help you estimate your total out-of-pocket cost.

Additionally, it’s important to know that COVID-19 vaccines are currently free to the public. That means that anyone within the United States can receive a COVID-19 vaccine free of charge. Use the search tool to find a COVID-19 vaccine or booster near you.

Vaccines are highly effective and safe. They’re used worldwide to prevent illness and death. These example statistics show how successful they’ve been — and how much more successful they could be with improved access.

  • Polio: Cases have decreased by more than 99 percent since a polio eradication campaign was initiated in 1988, according to the WHO. Today, polio is routinely found in only two countries (Afghanistan and Pakistan).
  • Prevention: Vaccines prevent 4 to 5 million deaths each year. Another 1.5 million could be prevented with expanded vaccine access. Between 2000 and 2018, the worldwide rate of measles deaths fell by 73%.
  • Rates: According to the CDC, 68.3 percent of American children receive the 7-vaccine series that’s recommended by age two. However, most vaccination rates for individual vaccines are higher.
  • COVID-19: By now, more than 50 million Americans have been vaccinated for Covid-19 and received an updated booster dose.

Vaccines can reduce disease, and ending vaccination could be very dangerous. For example, In 2000, measles had been declared eradicated in the U.S.

But, between the months of January and October of 2019, a total of 22 measles outbreaks comprising 1,249 individual cases were reported in the United States – the highest number of cases since 1992. Public health officials found that 89% of people that contracted measles during this period were unvaccinated or had an unknown vaccination status.

Even today, around the world, many vaccine-preventable illnesses and deaths still occur. This is because vaccines are not available to everyone. Because vaccines can prevent millions of deaths each year, one of the missions of the WHO is to increase vaccine availability worldwide.