Your Guide to Childhood Vaccinations Before Age 2

It is no secret that the issue of childhood vaccines has been prominent in the national conversation over the past several months. Robert F. Kennedy Jr. is well known for his vaccine skepticism, as are several other high-level appointees to the incoming administration. Even before this, in the wake of the COVID-19 pandemic, routine childhood vaccination rates have declined. 

With skepticism and, often, misinformation becoming more widespread, I have been getting more vaccine questions. Most parents are asking me questions — often, nervous ones. Anxiety here is a natural impulse. We want nothing more than to protect our children, and already, sticking needles into them can feel scary. As a friend said to me once, My baby is just so small. Do they really need all these shots? Add to that external conversations about possible links to autism or vaccine injury, and it’s not surprising that people have questions.

Public health messaging doesn’t always fully answer the questions people have, or provide enough information to navigate these choices. This article aims to close some of that gap.

I’ll go through each of the vaccines in the schedule in turn. I’ll explain the disease the vaccine protects against, the basic structure of the vaccine (when kids get them, how many shots), how effective the vaccine is, and whether there are any side effects to note. I then end with a few general questions about vaccines — how they work, why they’re important, and how we know they’re safe.

I’m focusing here on vaccines given through age 3. Many of these same vaccines are given as boosters later, and I’ve written elsewhere about one important vaccine, for HPV, which is given at age 11. 

Buckle up: this is a long article, and one I hope you’ll save and share.

What vaccines does my child need? 

I’m focusing here on the standard childhood vaccines, not on vaccines for COVID-19 and flu. 

The graphic below shows the full set of vaccines that the American Academy of Pediatrics recommends for ages birth to 3. Below, I’ll discuss them in roughly the order that they happen.

RSV

• What is RSV? Respiratory syncytial virus (RSV) is a common respiratory virus characterized by runny nose, sneezing, and congestion. It is common in the fall, and most people will get RSV many times in their life. For older children and healthy adults, it is generally not dangerous. For infants and older adults, it can be very dangerous, because it can settle in the lungs and affect breathing. 
• Vaccine basics: There are two ways to protect infants against RSV. Pregnant women can get an RSV vaccine during the third trimester of pregnancy. If that doesn’t happen, infants can get a monoclonal antibody shot at birth or anytime before eight months (this is not a true vaccine, as it delivers antibodies directly). Generally, you would choose one of these options, not both. This vaccine is only given in the first RSV season (i.e. fall/winter) for healthy infants and can be given shortly after birth. 
• How well does it work? RSV is common. In infants under six months, the hospitalization rate for RSV is 14.7 per 1,000; RSV causes 100 to 300 deaths per year in children under 5 in the U.S. In trials and real-world settings, either version of this immunization seems to reduce the risk of hospitalization for RSV by about 80%. 
• Additional notes: There was a concern when the vaccine for pregnant women was first approved about elevated rates of preterm birth. As the vaccine has rolled out, that has not been further supported in the data.

Hepatitis B

• What is hepatitis B? Hepatitis B is one of a number of hepatitis viruses that affect the liver. Acute hepatitis B infection can cause flu-like symptoms but is usually not serious. However, in a small share of cases, acute infection turns to chronic infection. This is asymptomatic but is a cause of liver cancer and liver failure. Hepatitis B is spread through bodily fluids, including from the mother at birth or in a day care setting. And babies and toddlers who are infected are much more likely to become long-term hepatitis B carriers than those who are infected older. This is why the vaccine is done in children.
• Vaccine basics: This is a three-dose series, with the first dose generally given at birth. This is done early because of the risk of transmission from the birth parent, if hepatitis B is undiagnosed. If you are sure you are not a hepatitis B carrier, some people will push the first dose to the two-month vaccines.
• How well does the vaccine work? There are approximately 13,000 acute hepatitis B cases per year in the U.S., mostly in adults. The vaccine provides between 80% and 100% protection against the hepatitis B virus. 

Rotavirus

• What is rotavirus? Rotavirus is a virus that causes severe diarrhea in infants and young children. It can cause severe dehydration, which may have serious consequences. Rotavirus infection is ubiquitous — most of us will get it many times — but it is more serious in babies and young children. The vaccine targets protection in this age group. Before widespread vaccination, the disease caused an estimated 55,000 to 70,000 hospitalizations and 30 to 60 deaths of children per year. 
• Vaccine basics: This vaccine is a two-dose series, typically given at two and four months, or a three-dose series (two, four, and six months). It is given orally, by putting drops in the baby’s mouth. The two vaccines have different dosing but similar efficacy and side effects, and your doctor is likely to use one or the other depending on their preferences.
• How well does the vaccine work? The vaccine is estimated to be 80% effective against rotavirus. 

DTaP

• What is DTaP? The DTaP vaccine protects against three diseases: diphtheria, tetanus, and acellular pertussis (whooping cough).
  • Diphtheria: A serious bacterial infection of the nose and throat. In the 1920s, this caused an estimated 13,000 to 15,000 deaths per year in the U.S. Currently it is extremely rare in the United States.
  • Tetanus: Tetanus is caused by a toxin produced by a bacterial infection, typically after an injury. Prior to vaccination, there were an estimated 500 tetanus cases in the U.S. per year. The current number is less than 50.
  • Pertussis: Otherwise known as whooping cough, this is a respiratory illness caused by bacteria. Prior to vaccination it caused several hundred thousand cases per year and an estimated 9,000 deaths in the U.S. Current case numbers are around 15,000 per year, with only 10 pertussis deaths per year in the U.S., mostly among young infants. However, pertussis rates have risen since a low in the early 1980s of under 5,000 a year.
• Vaccine basics: This vaccine is given at two months, four months, and six months. (There are also two boosters at 15 to 18 months and 4 to 6 years). Most women also get a related vaccine — Tdap — during pregnancy, which provides early protection to the infant. The Tdap vaccine protects against the same diseases, but because it’s a booster it has a lower dose of the pertussis vaccine.  
• How well does the vaccine work? Both diphtheria and tetanus are effectively unknown outside of unvaccinated individuals; estimates suggest an efficacy close to 100% for both. For pertussis, efficacy is estimated at 98% for a year following the last dose in childhood, and 70% five years after that. 
• Additional notes: This vaccine is typically given as a set covering all three diseases. There is a separate vaccine that covers only diphtheria and tetanus, but the pertussis vaccination only comes in the set. 

Haemophilus influenzae type b (Hib)

• What is Hib? Hib is a bacterial infection that can cause serious complications, especially in babies and small children, including meningitis and pneumonia. Before widespread vaccination, it caused an estimated 20,000 serious cases in the U.S., and 1,000 deaths. 
• Vaccine basics: Two doses at two months and four months, and a follow-up between a year and 15 months. (Sometimes a third dose is given at six months, depending on the timing of the first two.)
• How well does the vaccine work? The efficacy of these vaccines is about 95%. As a result of widespread vaccination, Hib cases are down over 99% relative to the period before vaccination. 

Pneumococcal conjugate vaccine (PCV)

• What is pneumococcal disease? This is a name for any infection caused by pneumococcal bacteria, which can cause a wide range of infections throughout the body, including blood infections, brain infections, pneumonia, ear infections, and sinusitis. The vaccine protects against a variety of pneumococcal bacteria.
• Vaccine basics: This vaccine is given as a four-dose series — two, four, and six months, and then 12 to 15 months.  
• How well does the vaccine work? The efficacy is 80%. Overall incidence of this disease in children has declined quickly since the vaccine has been introduced.  

Polio vaccine

• What is polio? A viral disease that causes paralysis and weakness. Paralysis can persist and spread to the spinal cord and brain, making it difficult to breathe. Seen pictures of kids in an iron lung? These were used in the 1950s for children who were paralyzed temporarily due to poliovirus. Polio outbreaks before vaccination were large and deadly. A 1952 outbreak in the U.S. caused an estimated 60,000 cases, 3,000 deaths (across all ages), and 20,000 cases of paralysis.
• Vaccine basics: The polio vaccine was developed in 1955 and was widely viewed at the time as a miracle. It is given in four doses — two months, four months, sometime between six and 18 months, and at 4 to 6 years. 
• How well does the vaccine work? Polio has been virtually eliminated in the United States. In 1979 the U.S. was declared polio-free. However, polio still circulates globally, which is why we still vaccinate children. Further, in 2022 an unvaccinated teenager in New York developed polio, which is a reminder that the virus is not gone. 
• Additional notes: If you want to feel really good about vaccines and the miracles of science, I highly recommend the book Polio: An American Story. 

MMR (measles, mumps, rubella) vaccine

• What is MMR? The MMR vaccine protects against three viruses.
  • Measles is a viral illness that causes a rash and flu-like symptoms. Prior to widespread vaccination, there were an estimated 3 million to 4 million cases and 400 to 500 deaths from measles per year in the U.S. Measles is extremely contagious, and the virus can live on surfaces for a long period of time.
  • Mumps is a contagious viral illness that causes jaw swelling, loss of appetite, and fatigue. Before vaccination, it caused about 160,000 illnesses per year in the U.S.
  • Rubella: A viral illness that causes a rash, fever, and sore throat. Sometimes called “German measles.” Generally mild; currently very rare in the U.S. 
• Vaccine basics: The MMR vaccine is typically given in a first dose between a year and 15 months, and a second dose at 4 years. If your child is at higher risk of measles exposure (for example, due to travel), doctors may do the first vaccine before age 1. However, children may in this case need three doses.
• How well does the vaccine work? Extremely well. Post-vaccination, both mumps and rubella are rarely seen in the U.S. In the case of measles, one dose of the vaccine provides an estimated 95% protection, and two doses provide an estimated 99%. This immunity seems to be durable through life and it is sterilizing, meaning that you cannot infect others with measles.
• Additional notes: Concerns are often raised about links between the MMR vaccine and autism. However, the data that underlies this idea was fabricated — literally, fabricated. The original paper on it was retracted, since the author had been dishonest about the selection of his sample of children and their symptoms. He was motivated, it seems, by a desire to have evidence to use in class-action lawsuits. In fact, there is a lot of excellent analysis showing no relationship between this vaccine and autism (here is just one example). 

Varicella (aka chickenpox) 

• What is chickenpox? If you are a child of the 1980s, as I am, you know. Viral illness. Itchy rash, fever, fatigue. Did I mention the itching? Before the vaccine, in the early 1990s, there were an estimated 4 million cases of chickenpox, over 10,000 hospitalizations, and 100 to 150 deaths per year. Generally, chickenpox is less serious when contracted in childhood, and having had it generates lifetime immunity. This is why my parents (like many others) had “chickenpox parties,” where they tried to purposely get us infected. 
• Vaccine basics: One dose at 12 to 15 months, another at age 4 to 6. This is sometimes combined with the MMR vaccine and, whether combined or not, is generally given at the same time.
• How well does the vaccine work? With two doses, the protection is 92% against any disease and over 98% against severe disease. Chickenpox is now quite rare in the U.S., with an estimated 150,000 cases per year. Relative to having had chickenpox, those who are vaccinated are also less likely to develop shingles as an adult. 

Hepatitis A

• What is hepatitis A? Hepatitis A is a contagious virus that causes liver disease. It’s spread through contaminated water and food, largely, or through poor personal hygiene. Before vaccination, children ages 2 to 18 had the highest rates of hepatitis. Prior to vaccination, the U.S. saw an estimated 270,000 infections annually. Though generally rare at this point, hepatitis A outbreaks became more common after 2016, relative to earlier years.
• Vaccine basics: Two-dose series, sometime between 12 and 24 months. 
• How well does the vaccine work? Efficacy is thought to be close to 100% after two doses, with ongoing protection for as much as 20 years. 

Vaccines 101

How do vaccines work?

When you get sick — with a virus or bacterial infection — your body makes antibodies to fight back. These are proteins that recognize, attach to, and kill whatever is causing the disease (the antigens). When you recover, your body retains these antibodies — and the memory of how to make them — so it can fight back more quickly if you are exposed to the same pathogen again. Vaccines work by exposing individuals to a virus or bacteria in a way that allows them to make antibodies against the virus or bacteria without making them sick. 

Generally, this is done by exposing people to a killed form of the bacteria or virus or a live but weakened version. When delivered in this way, people do not get sick, but their body, recognizing an unfamiliar invader, creates antibodies to fight it. If you are then exposed to the real thing, the actual live pathogen, you have antibodies against it and will not get sick (or not as sick).  

High levels of vaccination in a community overall can deliver herd immunity, where so many people are immune that the disease cannot get a foothold. This is important because it provides protection even for individuals who, for some reason, cannot get vaccinated themselves. This includes children who are too young for a vaccine, and those who have cancer or other immunocompromise. 

Why do kids need multiple shots of the same vaccine?

For a number of vaccines, the schedule involves multiple shots. This is because having multiple exposures gives a stronger and longer-lasting level of protection. For pertussis, for example, there is a 55% reduction in hospitalization risk in the first year if your child gets one dose, but 83% for two or three doses. 

Multiple shots of childhood vaccines happen for a different reason than seasonal vaccine boosters like flu or COVID. Those seasonal boosters are used because the viruses change over time. Childhood vaccine shots are the same across all doses; the goal is to enhance protection against a single pathogen.

What are general vaccine side effects?

Vaccines work by prompting an immune response in the body, which will commonly cause side effects like fatigue, fever, or crankiness. Many people find their child is in a bad mood after vaccines. This is an expected reaction to an immune challenge. It doesn’t mean the child has gotten sick from the vaccines.

There are some rarer side effects from vaccines. Children (or adults) can have allergic reactions. If the vaccine causes a fever, febrile seizures can happen (this is still rare but more likely with the MMR vaccine, in which it occurs in about 1 in 4,000 cases). And for children with immunocompromise, there are rare cases of more serious side effects from the measles vaccine.  

Generally, kids can be given Tylenol or (if they are over six months) ibuprofen to address vaccine side effects. These treatments do slightly reduce the levels of antibody production, but not enough to matter for efficacy. 

How do we know if vaccines are safe for children?

Vaccine safety is very heavily monitored by the government, in a system that is ingrained and will not change with a new administration. Before a vaccine is approved, safety trials are required. After approval, there is an adverse event reporting system, where doctors (or anyone else) can report adverse vaccine events. Many of these events are not actually due to the vaccines, but they are used to monitor. Because of this monitoring, even quite rare side effects can be identified.

This should give some broad safety reassurance. These vaccines have been given to millions and millions of children — in some cases hundreds of millions — which makes us confident that even rarer side effects would be seen if they were there. 

Is there a reason to space vaccines out?

Typically, many vaccines are given at once, at regularly scheduled well-child visits. Some parents consider spacing out vaccinations so they are not all given at a single visit. Is there any reason to do this? 

No. The immune system can respond to multiple challenges at once, so there is no reason to adapt the current vaccine schedule. Having said this: spaced-out vaccines are better than no vaccines, and if that makes you more comfortable with vaccinating, many doctors will be willing to do it. But it’s important to remember this agreement is generally not because they think it’s better to space them out than to do the normal vaccine schedule, but rather that some vaccines are better than none. 

Why are some vaccines more effective than others?

There are some vaccines — the childhood measles vaccine is a classic example — that are incredibly effective. A child who is fully vaccinated for measles is not only extremely unlikely to get measles but is also extremely unlikely to spread measles. This is because the immunity delivered by the measles vaccine is extremely durable, and the vaccine generally delivers what is called sterilizing immunity. Basically, the length of time the pathogen takes to replicate is sufficiently long that the immune system response is faster, and it never really gets going. The transmission of measles is therefore cut off.

There are other vaccines, like the seasonal flu vaccine, where the effectiveness is lower. One reason for this is that there is some guesswork in making the flu vaccine, and depending on how close the match of the vaccine is to the circulating form of the virus, efficacy may be more or less. It’s nearly always the case that a flu vaccine lowers the risk of getting the flu and makes it less severe if you do get it, but it doesn’t always fully protect you.

A lot of these viruses are rare now — why are we still vaccinating against them?

It’s clear that vaccination has been an incredible public health victory. Diseases that killed millions of people, including children, are now rare. The flip side of that is that parents may wonder, what’s the point? No one gets diphtheria anymore, so why give your kid the vaccine?  

The short answer is that it is only because of continued vaccination that these diseases are at bay. We have seen that pretty dramatically in the past several years, as measles vaccination rates have waned and measles outbreaks have occurred. The reality is that if we stopped vaccinating, a lot of these diseases would come back.

Get more from ParentData when you sign up

This article is part of your free preview. By signing up, you can get:

Access to ParentData

Newsletters delivered to your inbox

Community discussions with other data-driven parents

Sign up

Community Guidelines