Vaccine guidance from Mayo Clinic

Vaccines can protect against getting serious diseases that can harm or kill a baby, child or adult.

Vaccines also lower the chance that you or your child will spread a disease. This is important because some people can't get vaccines or don't have a strong immune response to vaccination. Newborns and older adults are in this category. Others who benefit from vaccinated people around them include people being treated for cancer, people taking medications that lower the immune response, people who have had transplants and people managing a chronic illness such as diabetes. They rely on others to get vaccinated and prevent the spread of disease.

Vaccines also can lower the risk of developing complications related to diseases. For example, the human papillomavirus, or HPV, vaccine prevents some types of cancers.

In general, a disease qualifies for a vaccine if it:

• Is common.
• Can be deadly or cause permanent disability.
• Can cause an immune response that can be copied.

A vaccine prepares your body to get rid of something that doesn't belong. Different vaccines use different methods for achieving this goal. A vaccine might be made of a weakened virus. It could have just the part of the virus or bacteria the immune system sees first. A vaccine might also be made of the proteins your body would naturally make to respond to the infection. That means during an actual infection, the bacteria or virus will be stopped before it has a chance to cause damage.

Some germs, such as the measles, don't change very much over time. So your immune system's memory, such as from when you were first vaccinated, protects you even decades after your vaccine. Other germs, such as influenza, often called flu, change, or mutate, enough every year that the immune system needs an update. Getting recommended adult vaccines can boost protection against these diseases. You might also be at risk for other diseases due to your job, lifestyle, travels, health or other factors.

No, it is always better to prevent infection by getting a vaccination than to get an infection and then treat it.

Many infections caused by viruses have no treatments. And some may lead to long hospital stays or death. For example:

• Chickenpox (varicella) infection can lead to skin infections, pneumonia and in rare cases, death.
• Polio infection can cause muscle problems or joint pain that gets worse over time, or permanent paralysis.
• Mumps infection could lead to deafness, temporary sterility or decreased fertility in men.
• Haemophilus influenzae type b (Hib) bacterial infection could lead to permanent deafness, brain damage or even death.

Some infections caused by germs, or bacteria, develop and worsen too quickly to be treated without complications. Or they may be hard to treat.

For example, tetanus is a disease caused by an infection with bacteria. As the bacteria grow, they release toxins and can block signals that travel from nerves to muscles. Tetanus is also called lockjaw because the toxins often cause muscles in the neck and jaw to stiffen. The vaccine for tetanus doesn't make people immune from infection. Instead, it prevents the damage done by the toxins. The vaccine is made of a disabled form of the toxin. As a result of vaccination, the body has learned to recognize the toxin and can quickly stop it during a real infection.

Vaccines lower the risk of getting a disease by working with the body's immune system. After vaccination, the immune system responds and remembers how to fight that virus in the future.

In 2009, researchers used vaccination data from 2005 to 2009 to estimate that routine vaccination of children prevented about 42,000 early deaths and 20 million cases, collectively, of diphtheria, tetanus, pertussis, Haemophilus influenzae type b, polio, measles, mumps, rubella, hepatitis B, varicella, pneumococcal disease, hepatitis A and rotavirus.

Each vaccine is designed based on how the body naturally reacts to an infection. Vaccine ideas are tested in a lab using simple models, like cells. The ones that work in cells are tested in animals. From there, the formulas that work best and have the fewest side effects are tested by human volunteers in clinical trials. If the vaccine shows a clear benefit, and benefits outweigh the risks, the vaccine maker can ask the U.S. Food and Drug Administration (FDA) to approve the vaccine to help prevent a specific disease. As part of the agreement, the FDA also examines the manufacturer and the manufacturing process.

Once the FDA approves a vaccine, a different group figures out how the vaccine should be used. This group is called the U.S. Advisory Committee on Immunization Practices (ACIP). Once the advisory group recommends a vaccine, the Centers for Disease Control and Prevention (CDC) and the FDA monitor its use for both safety and how well it works.

Because there was an urgent need for COVID-19 vaccines, the FDA's vaccine approval process happened at a faster pace than previous applications. The FDA first authorized COVID-19 vaccines for emergency use based on less data than is typically required. However, the data still had to show that the vaccines were safe and effective. This data eventually led to some vaccines getting complete approval. Others were given emergency use authorization.

See COVID-19 vaccines: Get the facts

The goal of one type of vaccine is to give you a very mild form of the disease it is created to prevent. These vaccines use a live but weakened germ, called an attenuated vaccine. A typical immune system can easily handle this type of germ. These vaccines may be given multiple times so the immune system builds up a good memory. But these vaccines can't be given to everyone. The ACIP defines who should and should not use attenuated vaccines.

For example, the group generally recommends against attenuated vaccines for people who are pregnant and others with immune systems that won't respond quickly or strongly to the vaccine. Instead, these people can use vaccines created around killed virus or bacteria, or ones that use only part of the virus or bacteria. The ACIP might also recommend that people with a slow-to-respond immune system get additional or higher dose vaccinations to make sure the body makes enough protection.

Some people think vaccinations make them sick because they have a headache, fever or other symptoms after getting a vaccine. But the immune system causes these symptoms. They are a sign that the immune system recognizes the vaccine and is preparing to fight the real infection.

Allergic reactions after vaccines are rare. When allergic reactions do happen, they often cause hives and itching all over the body. Some allergic reactions cause difficulty breathing or swallowing. These reactions are life-threatening and need treatment right away. Life-threatening reactions usually occur in the first 10 to 15 minutes after vaccination. These reactions can be treated effectively with medicine.

For many diseases, getting older increases the risk of a severe illness. The immune system responds more slowly to infection and vaccination. Unfortunately, people don't stop being exposed to infection as they age. For example, the influenza virus can infect people every season. A chickenpox infection can reoccur later in life as shingles. People who travel may get diseases that are not common where they originally grew up.

To balance the risk, vaccines are recommended by the ACIP for diseases that adults may get and have trouble clearing from their system. Depending on your age, lifestyle, job, travel, previous vaccinations and sexual habits, some vaccines can help prevent serious illness.

See Vaccines for adults: Which do you need?

Most babies are born with an immune system ready to keep out germs. For about three months after birth, babies also may get some protection from diseases to which their birth mother was immune or from their birth mother's vaccines. But vaccination makes sure a baby has as much protection as is safely possible and helps prevent babies and children from spreading infections to others.

The vaccine schedule covers common and dangerous infections such as:

• Viruses, such as rotavirus that can cause diarrhea and vomiting, leading to dehydration
• Infections caused by bacteria, such as those caused by Streptococcus pneumoniae in the ear, sinuses, blood, lungs, or the lining of the brain and spinal cord

See the Immunization schedule for people younger than 18

Timing is key. From birth, the ACIP recommends a schedule of vaccines designed to protect babies and children when their immune systems are ready and before they come in contact with the real infection. For example, some babies can be exposed to a virus called hepatitis B during birth. Hepatitis B causes liver damage that can lead to long-term infection and potentially liver failure. To manage that risk, the ACIP calls for that vaccine to be given right away, as soon after birth as possible.

But the schedule can be flexible. Some shots may be given early or planned in discussion with the health care provider. And in some cases, your baby's health care provider might suggest a vaccine out of order, such as during a local outbreak.

Many schools require that children be vaccinated to attend school, or before- and after-school child care. Vaccines are usually covered by state laws, not federal law. Required vaccines may be different depending on where you live in the United States.

Children who are not up to date on vaccines risk getting and spreading infections more easily. That could lead to health complications and missed learning time for a child, as well as missed work for caregivers. Ask your health care provider if your child is up to date on vaccinations.

See Vaccines: Keep your child's shots on track

Talk to your child's health care provider if you're concerned about the vaccine schedule. Getting vaccinated on schedule provides the best protection against illness. In general, children who are behind in their vaccines may have higher rates of vaccine-preventable diseases. They may also have trouble catching up on the vaccines that are due.

Newborns and young children can be exposed to diseases from family members, care providers and other close contacts. And they can be exposed during routine trips — such as visit to the grocery store. Many vaccines can be given even if your child has a mild illness, such as a cold, earache or mild fever. Talk your child's health care provider regularly to keep your child's vaccination status up to date.

See Childhood vaccines: Tough questions, straight answers

It's not a good idea to skip some vaccines. That leaves your child unprotected. It allows a child to spread disease to others. And because diseases are still spreading in the world, it puts your child at risk in the future. For example, in 1994 polio was considered eliminated in the United States. But since there are a few places in the world with regular polio outbreaks, the ACIP still recommends the vaccine for children or adults who missed that vaccination.

In recent decades, the only cases of polio in the U.S. came from people who caught the virus while traveling. But in July 2022, an unvaccinated young adult with no history of travel outside the U.S. was found to have polio virus. Public health investigators took specimens from the water treatment plant where the person lived. They found that polio was spreading in the community. But among the people who are vaccinated, getting polio is highly unlikely. Being fully vaccinated provides at least 99% protection.

And the ACIP reviews the vaccine schedule regularly.COVID-19 vaccinations are now on the schedule, for example. And the ACIP has recommended that a vaccine be removed. One example is the smallpox vaccine.

The last outbreak of smallpox in the U.S. was documented in 1949. The last case in the world was documented in 1977. The virus that causes smallpox had no one to infect, since so many people got vaccinated. It disappeared from the human population, which is called eradicated. Children in the U.S. were vaccinated against smallpox until 1972. But the ACIP removed it from the schedule because it's no longer a common threat.

If you have reservations about a certain vaccine, talk about your concerns with your child's health care provider. If your child falls behind the standard vaccines schedule, ask about catch-up immunizations.

See Childhood vaccines: Tough questions, straight answers

Vaccines do not cause autism. The original study that suggested this connection in 1998 was based on scientific errors. That study was removed from the scientific record in 2010.

See Childhood vaccines: Tough questions, straight answers

The COVID-19 virus is a coronavirus that spreads easily among people. A COVID-19 vaccine can prevent your child from getting COVID-19 and spreading it at home and in school. If your child gets COVID-19, a COVID-19 vaccine could prevent severe illness. While children are less likely to become severely ill with COVID-19, some children need to be hospitalized, treated in the intensive care unit or placed on a ventilator to help them breathe. Rarely, children who get COVID-19 develop a serious condition called multisystem inflammatory syndrome in children (MIS-C). Children can also experience long-term health effects due to COVID-19.

Vaccines teach the immune system to recognize the COVID-19 virus in different ways. Two COVID-19 vaccines contain genetic instructions for a piece of the virus that causes COVID-19. Those instructions, called messenger RNA, use your cell's machinery to make proteins the virus would use to infect a cell. After the vaccine injection, your cells follow these instructions and make the viral proteins. When your immune system locks onto those proteins, it forms a memory that helps prevent serious illness when the complete virus makes it into the body. These vaccines are known by their manufacturers: Pfizer-BioNTech and Moderna.

Another type of COVID-19 vaccine does not send instructions to the cells. It has the actual protein pieces of the COVID-19 virus. The immune system responds directly to those proteins and forms a memory to fend off infection in the future. That vaccine is made by Novavax and is authorized for children age 12 and older.

Find out about precautions and side effects of the COVID-19 vaccine for kids.

This vaccine shouldn't be given to a child who has:

• Had a severe allergic reaction after a previous dose of this vaccine
• Had a severe allergic reaction to any of this vaccine's ingredients

See more:

• COVID-19 vaccines for kids: What you need to know
• COVID-19 in babies and children

Influenza (flu) is a lung (respiratory) infection that can cause serious complications, especially in young children. Complications can include pneumonia and ear infections. And it can cause asthma flare-ups.

The flu vaccine can lower your child's risk of the flu and its severity. And it can lower your child's risk of needing to stay in the hospital due to serious illness from the flu. The flu vaccine causes your child's body to make antibodies to protect against the flu.

The CDC recommends a flu vaccine every year for everyone age 6 months or older. The flu shot can cause some side effects and has some precautions. If your child has an egg allergy, your child can still get a flu vaccine. Each year's flu vaccine provides protection from the flu viruses research expects to be the most common during the year's flu season. The vaccine is available as a shot, or injection, and as a nasal spray. Children under 2 shouldn't get the nasal spray. Find out about the nasal spray side effects and precautions.

Tetanus is a serious disease that causes muscle contractions, particularly in the jaw and neck muscles. The bacteria that cause tetanus enter the body through cuts or wounds. Severe complications of tetanus infection can be life-threatening.

Diphtheria is a serious infection that usually affects the mucous membranes of the nose and throat. In advanced stages, diphtheria can damage the heart, kidneys and nervous system. Even with treatment, the disease can be deadly, especially in children. Diphtheria is rare in the U.S., thanks to widespread vaccination. But many countries still have high rates of diphtheria.

Whooping cough (pertussis) is a highly contagious respiratory tract infection. It often causes a severe hacking cough followed by a high-pitched intake of breath that sounds like "whoop." Among children, whooping cough mainly affects kids too young to be fully vaccinated and teens whose immunity has faded. The infection can be deadly in infants.

The Tdap vaccine is used to boost a child's immunity to tetanus, diphtheria and whooping cough. Birth mothers get the Tdap vaccine during pregnancy to provide some protection against whooping cough to newborns. The ACIP recommends babies get three doses during their first year, and two additional doses before age 7. After age 18, ACIP recommends everyone get a Tdap, or at least at tetanus vaccine, every 10 years.

The Tdap vaccine uses inactive, weakened versions of the tetanus, diphtheria and pertussis toxins. After vaccination, the body begins building an immune response against these toxins. The Tdap vaccine is 94% to 100% effective in preventing tetanus and diphtheria. Protection lasts about 10 years. The Tdap vaccine is 85% effective in preventing pertussis. Protection lasts 1 to 2 years.

Find out about precautions and side effects of the Tdap vaccine.

This vaccine shouldn't be given to a child who has:

• A history of an allergic reaction to any previous dose of a vaccine that protects against tetanus, diphtheria or pertussis
• A history of coma, decreased level of consciousness or prolonged seizures within seven days after a previous dose of any pertussis vaccine
• Any severe, life-threatening allergies
• Seizures or another nervous system problem
• A history of Guillain-Barre syndrome
• A history of severe pain or swelling after a previous dose of any vaccine that protects against tetanus or diphtheria

Meningococcal disease is a rare, severe bacterial infection that can cause permanent disabilities or death. The bacteria that causes the disease can infect the fluid and membrane surrounding the brain or spinal cord, a disease called meningitis. Or it can enter the bloodstream or spark an infection in the joints or heart.

Anyone can get meningococcal disease. Among children, meningococcal disease is more likely to affect infants younger than age 1 and adolescents and young adults ages 16 through 23. It's also more likely to affect children with certain medical conditions that affect the immune system. Young adults living in groups, such as in college or during military training, may be at higher risk than the average person.

The meningococcal conjugate vaccine can help protect against meningococcal disease caused by the bacteria strains A, C, W and Y. This vaccine is given as one shot. It is routinely recommended at age 11 or 12. A booster dose involving one shot is recommended at age 16. This vaccine can also be given to children between the ages of 2 months and 10 years who are at high risk of bacterial meningitis or who have been exposed to someone with the disease.

The meningococcal ACWY vaccine uses inactive parts of the A, C, W and Y bacteria strains. After vaccination, the body begins building an immune response against the bacteria. The meningococcal ACWY vaccine is 80% effective at preventing meningococcal disease one year after vaccination. But protection gradually fades over five years. That's why it's important to give the booster dose at age 16, when the risk of meningococcal disease increases.

Find out about precautions and side effects of meningococcal ACWY vaccine.

This vaccine shouldn't be given to a child who has:

• A history of an allergic reaction to any previous dose of a meningococcal ACWY vaccine
• Any severe, life-threatening allergies

Human papillomavirus (HPV) is a virus spread mainly by skin-to skin contact. HPV infection is often spread through sexual contact. HPV infections can cause warts and many kinds of cancer.

The HPV vaccine can prevent cancer of the cervix, vagina and vulva. The vaccine can also prevent genital warts, and cancers of the anus, penis and back of the throat. The HPV vaccine can protect against more than 90% of cancers caused by HPV.

The ACIP recommends routine HPV vaccination for kids ages 11 and 12. Kids and teens can get the HPV vaccine as early as age 9 or at ages 13 and 14. Two doses of the vaccine are given at least six months apart. It's ideal for people to get the vaccine before they have sexual contact and get exposed to HPV. Research has shown that receiving the vaccine at a young age isn't linked to an earlier start of sexual activity.

Once someone is infected with HPV, the vaccine might not be as effective or might not work at all. Also, response to the vaccine is better at younger ages than older ones.

Teens and young adults who begin the vaccine series later, at ages 15 through 26, should get three doses of the vaccine.

Find out about the precautions and side effects of the HPV vaccine.

Generally, vaccines that contain killed or inactivated germs can be given during pregnancy. Vaccines that contain live, weakened viruses aren't recommended during pregnancy. For example, the chickenpox vaccine isn't recommended during pregnancy. Otherwise, vaccines recommended during pregnancy can help both mother and fetus. A flu shot and the vaccine against tetanus, diphtheria and pertusses help a pregnant person avoid those illnesses and any complications they could add to the pregnancy. But they also help protect newborns before they can be vaccinated.

See Which vaccines are recommended during pregnancy and which ones should I avoid?

Vaccination is safe for women who are breastfeeding with two exceptions. Because of the potential risk for passing the virus to a baby, smallpox vaccination and the yellow fever vaccine should be put on hold while nursing. But if a person is traveling to areas where they may get yellow fever, the ACIP recommends going ahead with that vaccination. Otherwise, killed or weakened viruses and bacteria used in vaccinations are safe and effective in people who are breastfeeding.

Because vaccines cause an immune system response, they might contribute to temporary menstrual cycle irregularity or changes in menstrual flow. Of the research that exists, some shows that infection or fever can cause altered cycles. No vaccines have been shown to interfere with a person's fertility.

The flu shot is recommended for people who are pregnant during flu season. Getting the flu shot during pregnancy can protect you from infection and can also help protect your newborn before vaccination is possible. This is important because the flu can be particularly dangerous for infants.

See Which vaccines are recommended during pregnancy and which ones should I avoid?

Tetanus is a serious disease that causes muscle contractions, particularly in the jaw and neck muscles. The bacteria that cause tetanus enter the body through cuts or wounds. Severe complications of tetanus infection can be life-threatening.

Diphtheria is a serious infection that usually affects the mucous membranes of the nose and throat. In advanced stages, diphtheria can damage the heart, kidneys and nervous system. Even with treatment, the disease can be deadly, especially in children. Diphtheria is rare in the U.S., thanks to widespread vaccination. But many countries still have high rates of diphtheria.

Whooping cough (pertussis) is a highly contagious respiratory tract infection. It often causes a severe hacking cough followed by a high-pitched intake of breath that sounds like "whoop." The infection can be deadly in infants.

One dose of Tdap vaccine is recommended during each pregnancy, regardless of when you had your last Tdap or tetanus-diphtheria (Td) vaccination. Receiving the Tdap vaccine during pregnancy helps protect your newborn from whooping cough (pertussis). Ideally, the vaccine should be given between 27 and 36 weeks of pregnancy. Getting the Tdap vaccine during pregnancy can protect you from infection and can also help protect your newborn before vaccination is possible.

Find out about precautions and side effects of the Tdap vaccine.

See Which vaccines are recommended during pregnancy and which ones should I avoid?

If you're pregnant and haven't already gotten a COVID-19 vaccine, the COVID-19 vaccine is recommended during pregnancy. Studies have shown COVID-19 vaccines don't pose any serious risks for people who are pregnant or their babies.

Getting the COVID-19 vaccine during pregnancy can protect you from infection and serious illness. It can also help protect your newborn before vaccination is possible.

See Which vaccines are recommended during pregnancy and which ones should I avoid?