Childhood Vaccines: Frequently Asked Questions

All vaccines train the body’s natural defenses (the immune system) to identify and fight specific germs. This allows the body to respond quickly and effectively if exposed to the real infection.

Yes, vaccinated people can and sometimes do catch an infection, even if they have been vaccinated against it. No vaccine is 100% effective, but people who are vaccinated are less likely to become infected than people who are not vaccinated.

When vaccinated people get sick, their illness is usually milder and less likely to cause health problems than in unvaccinated people.

How well a vaccine works depends on the type of vaccine and the infection it is protecting against. For example, two doses of the measles, mumps, and rubella (MMR) vaccine has been shown to be 97% effective at protecting people from measles for life. This is in part because the measles virus is a stable virus and has not changed much over the years.

In contrast, the flu virus is constantly changing, and there are many different strains. That is why the flu vaccine is recommended every year for everyone 6 months and older. Sometimes people still get the flu after being vaccinated, but the flu vaccine still protects them from severe illness and complications.

No. Getting the disease may provide immunity, but it comes with real risks that vaccines are designed to avoid. Natural infection means a child has to get sick and can get others sick.

Many diseases that vaccines can prevent may cause serious complications like lung infections (pneumonia), brain swelling, long-term disability, or even death. Even healthy kids can have serious complications when they get sick.

Vaccines give the immune system a safe “practice run.” They build strong protection without exposing a child to the dangers of the disease itself. Vaccination offers the benefits of immunity with far less risk.

No. Hygiene and good nutrition are important for wellbeing. Handwashing can help reduce the risk of infection, and having good health can improve outcomes when kids get sick. However, this is not a substitute for vaccination.

Vaccines work with the body’s natural defenses to create built-in protection against specific diseases. They often prevent illness before it happens. Vaccines offer a level of targeted protection that healthy habits alone cannot provide.

You can practice hygiene, good nutrition, and vaccination all at once. This is the best way to set up your child for a long, healthy life.

Diseases that seem “mild” can still be very serious — especially for babies, young children, and people with certain underlying health conditions.

Even healthy people can become very sick. The diseases that we have vaccines for can cause serious complications or lifelong disability. Sometimes new complications can develop later in life from these illnesses.

For example, about 1 in 5 unvaccinated people in the U.S. who get measles will be hospitalized. About 1 out of 1,000 people with measles will develop brain swelling, which could lead to brain damage. The risk is higher in children younger than 5. Even if your child fully recovers from a measles infection, there is still risk. The infection can cause “immune amnesia,” which makes your child more likely to get other infections for years.

Another example is varicella (chickenpox). Chickenpox may seem like just an itchy uncomfortable week for your child, but it can cause serious complications. Your child could get serious infections or bleeding problems. Later in life, the varicella virus can become active again and cause shingles, a painful nerve condition. Studies show that the varicella vaccine also greatly reduces the chance of shingles.

Pertussis (whooping cough) may seem like just a cough, but it’s not. Whooping cough can cause complications ranging from less serious issues like ear infections and dehydration, to pneumonia, brain damage, and death. Even a normal course of illness can include uncontrollable or even violent coughing for one to six weeks. About 30% of babies under 1 year who get whooping cough need care in the hospital. About 1% to 2% will die.

New York City is a global city with a high population density, with many people coming in and out and living close together. There is always a risk of a disease entering and spreading. Vaccination is all the more important here.

Many diseases are uncommon now because of vaccination. As less people get vaccinated, those diseases can come back. We are seeing this happen right now.

For example, in the early 2000s, there were fewer than 100 measles cases per year in the U.S., and these cases were related to foreign travel. More recently, we have seen the disease spread locally. Between 2018 and 2019 there was a large measles outbreak in NYC with over 600 confirmed cases.

In 2025, there were several outbreaks of measles in the U.S. and a total of 2,280 confirmed cases. These outbreaks are directly connected to decreases in vaccination rates.

Pertussis (whooping cough) is another very contagious and serious disease. Before the vaccine became available in the 1940s, about 200,000 children in the U.S. got the disease each year. After the vaccine became available, the number of cases in the U.S. dropped to a historic low of 1,010 in 1976. As vaccination decreases, there have been many more cases. In 2024, there were over 35,000 reported cases in the U.S.

Polio is a dangerous disease that used to paralyze more than 15,000 people in the U.S. annually, mostly children. Thanks to vaccination, the U.S. went nearly 10 years without any cases of polio. Then, in 2023, a case of polio caused paralysis in an unvaccinated man in New York State.

For some infections, yes, in part. Herd immunity happens when enough people in the community are vaccinated, making it harder for a disease to spread. Everyone needs to do their part for herd immunity to work. Also, while herd immunity reduces the risk of your child being exposed, it does not protect them if they are exposed. Even if your community has herd immunity, vaccinating your child is important in case you travel to places with low vaccination rates.

Herd immunity is especially important for people who cannot be vaccinated. That includes infants too young to be vaccinated and people for whom vaccines don’t work as well, such as people who have weakened immune systems. Herd immunity is also especially important in New York City, where diseases can spread quickly.

Vaccine side effects are usually mild to moderate: a sore arm where your child got the shot, low fever, or fussiness. While it is hard to see your child uncomfortable or in pain, side effects are a normal response to vaccines. Vaccines trigger an immune response. Side effects show that the body is building immunity, which is a positive and expected reaction.

Medicine and science aren’t perfect and are always improving. No medication or procedure is 100% without risk. Complications from vaccines, such as a serious allergic reaction, are rare, but they are possible. Vaccination recommendations weigh the risk against the benefits.

For example, the risk of a serious allergic reaction from the measles, mumps, and rubella (MMR) vaccine is 1 per 300,000 children. But, 1 to 3 people out of every 1,000 who get sick with measles will die, so vaccination is the far safer choice.

If your child has a weakened immune system, talk to their doctor to find out which vaccines are safe for them. Children with weakened immune systems can generally get all the routine vaccines except for live vaccines. Their doctor will be able to give the best recommendations for their specific circumstances.

It’s completely understandable to feel concerned when you hear stories like that. It’s important to remember that personal stories don’t always provide the full picture. Just because two things happen around the same time doesn’t mean one caused the other.

For example, children often get vaccines around the same age that autism or learning challenges start to show up. This timing can make it seem like the vaccine caused the issue. Extensive research has shown that vaccines are not the cause.

Also, stories reflect just one vaccination event. Any vaccine complication needs to be looked at in the context of the hundreds of millions of vaccine doses given every year in the U.S. alone.

If you are worried about your child’s specific health or medical history, talk to your child’s doctor.

Most vaccines contain either an inactivated (killed) form of the virus or bacteria or only specific parts of it, so they cannot cause the disease.

A small number of vaccines contain a greatly weakened form of the virus or bacteria. These vaccines are called live attenuated vaccines, or live vaccines. For almost everyone, live vaccines are safe and do not cause the disease they are designed to protect against.

In rare cases, people with very weak immune systems may not be able to get live vaccines because they could develop a case of the illness. Examples of live vaccines are the measles, mumps, and rubella (MMR) vaccine and the varicella (chickenpox) vaccine.

Thimerosal has been used for decades to prevent the growth of bacteria and fungi in certain medicines and vaccines. Research has shown that thimerosal is a safe ingredient in vaccines. It does not cause autism or neurological problems.

Thimerosal was removed from vaccines because of misleading claims about mercury. Thimerosal contains ethylmercury, a type of mercury that is quickly eliminated by your body and does not cause harm. Ethylmercury is different from methylmercury, the type of mercury found in certain fish that can be harmful in large amounts.

The decision to not allow thimerosal in flu vaccines was troubling because it was not based in science. Banning vaccine ingredients without evaluation of the facts sets a risky precedent that could reduce access to important medicine and technology. This ultimately makes everyone less safe.

No. A 1998 study that claimed to show a link between vaccines and autism has long been discredited and was retracted. The doctor who wrote it had his medical license revoked. Since 1998, independent researchers have done over 40 high-quality studies with more than 5.6 million people. All have reached the same conclusion: There is no link between vaccines and autism.

Despite strong evidence, some people use a limitation of science to create doubt. Science tests specific ideas such as “vaccines do not cause autism,” but it cannot fully prove something is impossible. It can only prove repeated failure to support a claim.

Imagine a study to see if people can fly. If a million people are asked to jump off a chair and try to fly and no one can, we still haven’t proven that it is impossible to fly. If there is another study comparing humans to birds that shows humans are not built in a way to be able to fly, that still hasn’t proven no human can fly.

Scientists are still studying potential causes of autism, such as genetics, parents’ age, and factors in the environment. There is no single root cause of autism. A combination of influences is likely involved. There is widespread scientific consensus that vaccines are not one of the causes.

Pharmaceutical companies must follow strict rules to prove vaccines are safe and work well before they can be used. In order for vaccines to be approved, vaccine safety is checked by independent experts.

Vaccines continue to be monitored for safety even after being approved. If there is a problem that was not known, changes can be made to recommendations. Pharmaceutical companies do not set vaccine schedules or decide who should get vaccines.

Health care providers are paid for vaccination, as they are for other services. However, over half of pediatric practices break even or lose money on vaccinations. This is because purchasing, storing, and handling vaccines is expensive. A survey found that nearly 10% of pediatricians considered stopping vaccine services due to the financial burden.

Providers recommend vaccination because it protects children from serious disease.

Infants are more likely to get certain diseases because their immune systems have not yet fully developed. For the same reason, infants and young children are often at greatest risk of severe illness and complications if they do get sick. Immunizing your baby following the recommended schedule is the best way to protect them from the diseases the vaccines prevent.

Children born before the 1990s received fewer vaccines than today’s kids. For example, in 1982, the schedule for children under 2 included vaccines against seven diseases. Today, the schedule for children under 2 includes vaccines against 15 diseases. This is thanks to advances in research that have led to many new vaccines that have further reduced childhood illness. Vaccines can now protect your child from Haemophilius influenza type b (“Hib”), varicella, pneumonia, and rotavirus.

What matters more is what is in the vaccines, not how many there are. If you add up all the immunological components in the 15 vaccines that children receive today, it comes out to about 180 components. In the 1980s, the seven vaccines that children received had about 3,000 components. Thanks to advances in technology, today’s vaccines are more efficient and place less demand on children’s immune systems than they did in the 1980s.

The vaccine schedule was designed to safely protect children from serious diseases as early in your child’s life as possible. Vaccines have been carefully tested to make sure they work well when given together and that doing so does not create any safety issues.

This is not recommended. Young children are at higher risk of getting a disease that could have been prevented by a vaccine. They are also at higher risk of getting very sick and having complications if they are infected. This is why vaccines are given as early as possible in childhood.

The American Academy of Pediatrics vaccine schedule maximizes your child’s protection against infections. For each vaccine, the recommended age, number of doses, and time period between doses were decided based on study data.

The doctors who created the schedule considered when a child’s immune system is ready to respond most effectively and when a child is most at risk of catching a disease.

There is no research to show that a different schedule is better or that spreading out vaccines is safer.

What we do know is that your child is not protected from the disease during the time they are not vaccinated.

If you are considering delaying any vaccines, make sure you talk your child’s doctor. It’s important for your child to get all recommended vaccines, but their doctor can decide which ones are most urgent based on risks like travel. If your child is attending day care or school in New York City, your child must meet day care or school vaccination requirements.

School and day care vaccination requirements are determined by New York State and New York City law. These requirements haven’t changed in many years. Updates to the vaccine schedule don’t affect what your child needs for school.

Learn more about what immunizations are required for NYC Public Schools.

For decades, the NYC Health Department’s vaccine recommendations aligned with the CDC. Until recently, the CDC was a trusted source of vaccine information. The CDC used to make recommendations only after careful review of all available information. Experts at the CDC relied on an independent group of doctors and other experts.

Unfortunately, that is no longer true. The CDC did not even talk to their own staff or advisory panel before they made major changes to the vaccine schedule. The recent changes to the CDC schedule depart from longstanding scientific evidence. Current CDC recommendations no longer offer the best way to prevent illness in children.

The NYC Health Department has endorsed the American Academy of Pediatrics (AAP) schedule for vaccination. AAP has long been a trusted source of vaccination information. Doctors there have studied childhood vaccines and issued recommendations for decades.

AAP’s 2026 schedules continue to recommend immunizations based on rigorous research. They have been endorsed by 12 leading medical and health care associations.