Vaccination FAQs

What research supports that vaccines are safe?

An overwhelming number of studies by today's leading organizations and top scientists have shown that today's vaccines are safe and effective at preventing disease and infection. See The Proof Behind Vaccine Safety and the Centers for Disease Control and Prevention's Resource Library for more details on supporting research.

What organizations agree vaccines are safe?

The New York State Department of Health, along with the American Academy of Pediatrics, the Centers for Disease Control and Prevention, the American Medical Association, the American Academy of Family Physicians, the National Association for Pediatric Nurse Practitioners, the Children's Hospital of Philadelphia, the Gates Foundation, the Infectious Diseases Society of America, the Canadian National Advisory Committee on Immunization, the Department of Health of the United Kingdom and many other reliable organizations around the world all agree vaccines are safe and save lives.

Is thimerosal safe?

Yes, but even so, thimerosal is not in any routinely recommended childhood vaccines except the flu vaccine. And even with the seasonal flu vaccine, thimerosal-free versions are available. Although some attention has been placed on thimerosal, a vaccine preservative, there's no proof that it's harmful. Thimerosal is an organic form of mercury (also called ethlymercury) that prevents bacteria from contaminating vaccines. This form of mercury is completely different from methylmercury, which can damage the nervous system. Still, public concern over its potential to do harm has prompted the U.S. Food and Drug Administration and vaccine manufacturers to develop thimerosal-free vaccines.

How can flu vaccines come out so fast and still be safe?

Vaccines typically take 10 to 15 years of research (, development and testing before being approved by the U.S. Food and Drug Administration (FDA) and made available to the public. One exception to this time frame is the flu vaccine. The reason for this is that the manufacturing process for the flu vaccine remains unchanged. The only thing that changes each year is the antigen. Founded on ongoing virus tracking around the world, scientists determine which flu viruses are most likely to circulate during the next flu season. Once the viruses are identified, scientists change the antigen in the vaccine but keep everything else the same. The College of Physicians of Philadelphia provides a comprehensive explanation on how vaccines are developed ( and rigorously validated ( If you're a parent with questions about the process, the AAP offers information specific to childhood vaccines ( For an interactive exploration of how vaccines play an integral part of our lives, as well as an in-depth look into vaccine science, visit the History of Vaccines.

Why are there so many more vaccines today compared to when I was a kid? (

As science and medicine continue to evolve, so does our ability -- and public health responsibility -- to prevent disease. The results of some of these advancements are new vaccines. The current U.S. vaccination schedule for children between birth and six years old recommends immunizations for at least 15 different diseases that may cause significant health problems and even death. Although this number may seem like a lot, it's important to know each and every disease has the potential to quickly reappear if vaccination rates drop.

How are vaccines made and tested?

The development and evaluation of vaccines is one of the most sophisticated medical processes in the world. Vaccine development is highly regulated, requiring years of research and testing before it's licensed for public use. The vaccine is first tested in the laboratory; then, if proven successful and effective, it is tested in several clinical trials involving groups of volunteers. The plant where the vaccine is manufactured, as well as the process of making the vaccine, is also inspected. Even after a vaccine has been approved by the U.S. Food and Drug Administration, the vaccine continues to be analyzed regularly, and there are international systems in place to track outcomes. For more information, see The Science Behind Vaccine Development and Testing.

What are the side effects of vaccinations?

The most common side effects are a low-grade fever, mild aches, and swelling and redness or soreness at the injection site. These are signs that the vaccine is working and the body has been activated to build a defense against the disease. In very rare cases, a person could have an allergic reaction and should seek medical attention. This only happens to one in 1 million people. Contrary to popular belief, getting a seasonal flu vaccine does not cause you to get the flu. For more information, see Common Misperceptions and Concerns Explained.

Where can I get my child vaccinated?

Visit your child's pediatrician for personalized care and to get the appropriate vaccines. The New York State Vaccines for Children Program also provides vaccines at no cost to eligible residents; visit our Vaccines for Children Program page, email or call 800-543-7468 for more information. You also can receive vaccinations at your local county health department.

Do vaccines cause autism?

No. A large body of medical evidence indicates that vaccines and autism are not linked. See The Truth About Autism for more details about this controversial subject.

Does my child really need a flu vaccine every year?

Yes. It is recommended that everyone older than 6 months receive a seasonal flu vaccine annually. Children are particularly at risk for contracting the flu because of the time they spend at school and play. Getting vaccinated is even more critical if your child has a chronic condition, like asthma or diabetes, that makes him or her more prone to being infected and can make their chronic condition worse. Nearly 20,000 children under age 5 are hospitalized in the United States every year due to flu-related complications (, and many of these cases result in death. Avoid the possibility of this happening to your child.

How bad is it to delay the recommended vaccine?

The more you delay, the more you increase your risk of exposure to a long list of serious, and potentially crippling or deadly diseases. There are many consequences to delaying or not following the vaccination schedules recommended by the New York State Department of Health, Centers for Disease Control and Prevention and the American Academy of Pediatrics. To find out more, see The Harm of Delaying or Skipping.

What does it mean if my child has a fever after getting vaccinated?

A mild fever that goes away in a day or two is not uncommon. Mild fever is actually a sign that the vaccine is working. However, if the fever persists, or increases in temperature, or if your child is exhibiting other symptoms that the nurse or pediatrician did not mention, seek medical attention promptly.

Does my child really need to get vaccinated for diseases that are no longer around?

Yes. Infectious diseases, by nature, spread quickly among those who are not protected. Even if the disease is considered rare or under control, there is still danger of it reemerging. We've seen this before, in the recent U.S. mumps and whooping cough outbreaks following drops in vaccination rates, which resulted in severe health consequences for many patients as well as a public health scare.