Side Effects Of Vaccines In Babies:  what you can do and Why you should not worry

image: iStockphoto


Vaccines for babies are given to protect them from vaccine-preventable infectious diseases such as polio, whooping cough, and measles. All the vaccines go through a series of testing and are approved by the concerned authorities before they are allowed to be given to the public. Vaccines consist of a weakened or dead form of the pathogen, which causes the respective disease. When injected, the body reacts and produces antibodies against the pathogen, providing immunity for the long run (1).

Parents are often concerned about the side effects of certain vaccines for their children. Read on to know about the safety of vaccines, including their side effects.

Are Vaccine Side Effects Possible?

Although vaccines are completely safe, like medicines, they too may sometimes cause side effects. There could be various factors that could determine whether a baby is likely to display a vaccine’s side effects.

What Factors Influence Vaccine Side Effects?

The type, intensity, and duration of side effects may depend on the following factors related to the baby’s health (2)(3)

  • History of acute allergic reactions to most vaccines
  • Chronic conditions, such as congenital heart disease associated with immune deficiency or transplantation
  • Medications or treatment of illnesses, such as cancer
  • Suppressed immunity or weakened immune system due to various problems, such as HIV
  • Immune system-related problems, such as Guillain-Barré Syndrome

Some vaccines are recommended at a specific age to prevent the risk of adverse side effects. Babies with the aforementioned conditions may be able to receive certain vaccines, and not all babies with these conditions display severe side effects.

How Long Do Vaccination Side Effects Last?

Most side effects of vaccines are mild and usually last for a day or two (4). Some vaccines may cause side effects that may last for five to seven days. However, these effects are mild and seldom cause any severe discomfort to the baby.

Why Do Babies Have Vaccine Side Effects?

Vaccines contain dead or weakened disease-causing bacteria or viruses that stimulate the body to make antibodies. It is similar to catching the pathogen but without developing serious symptoms and complications of the infection (5). However, the heightened immune response could temporarily lead to mild symptoms of infection, such as fever. These symptoms are known as side effects.

Common Side Effects Of A Vaccination In Infants

Below are some of the common vaccine side effects, which are mostly mild (6).

  • Fever: Fever usually appears within 24 hours after immunization and subsides within one to two days.
  • Reaction at the site of the shot: Redness, pain or tenderness, and swelling around the site of the shot are common occurrences. The symptoms usually start within 24 hours and may last up to three to five days. In the case of the DTaP vaccine (diphtheria, tetanus, and pertussis) vaccine, the local reaction may last up to seven days.
  • Formation of a lump: A small, hard lump or nodule may develop at the site of the shot. This lump may be present for a few days and requires no treatment.
  • Sleepiness: Babies may feel unsettled, sleepy, or lethargic after vaccination. Some babies may sleep more than normal for a day or two after vaccination.
  • Irritability: Fussiness is also a common side effect in babies.
  • Delayed reaction: In the case of MMR (measles, mumps, and rubella) and chickenpox vaccines, babies may experience fever and rash. However, these symptoms usually occur later, between one and four weeks after vaccination, and last for a day or two.

Are There Serious Side Effects Of Vaccines?

Severe allergic reactions in babies are rare and occur in one to two cases out of one million vaccinations (7). Below are some of the rare and uncommon adverse side effects of vaccines in babies (8).

  • Anaphylaxis: It is a severe allergic reaction, which usually starts within 20 minutes and can last up to two hours. Healthcare providers are equipped to control this reaction, and it is completely reversible when addressed quickly.
  • Febrile seizure: It primarily occurs when the baby’s fever rises very quickly. The seizure may last for a minute or two. However, it usually does not cause any permanent harm or damage to the child.
  • Intussusception: It is a condition where one section of the intestine collapses on another, leading to bowel blockage. Intussusception due to vaccination is extremely rare in babies and may usually occur if they have existing health problems or anomalies.
  • Fainting: Some babies may experience dizziness and lose consciousness after vaccination.
  • Very high fever: In rare cases, the baby experiences a very high fever with a body temperature of nearly 104°F (40°C).
  • Change in heart rate: Some babies may experience a rapid and sustained increase in the heartbeat.
  • Physical side effects: Some of the rare adverse physical side effects include discoloration of the legs, swelling of the limb or body part where the shot was given, and rashes all over the body.

What To Do If Your Baby Has Vaccine Side Effects?

You may talk to your healthcare provider about the possible side effects and how you can be prepared to manage the common side effects at home. Most side effects of vaccines are mild and can be managed with the following homecare methods (4) (5).

  • Keep the baby hydrated with extra breastfeeding sessions. Babies older than six months can be provided with other fluids, such as broth and soups.
  • If your baby has a fever, do not overdress them. Keep their room well-ventilated to prevent overheating.
  • If you see a local reaction at the site of the shot, place a cold, wet cloth to reduce discomfort.
  • Let the baby have adequate rest and avoid physical exertion for a day or two after vaccination.
  • You may speak to your doctor and ask them to prescribe acetaminophen for your baby. Avoid self-medication to avoid other potential side effects.

When To Call A Doctor?

Consult a doctor soon if you observe any severe side effects of vaccination. You must also see a doctor in the following scenarios (6).

  • High-pitched crying for more than one hour after vaccination
  • Vomiting or diarrhea after a vaccination
  • Redness around the site of the shot becomes larger than one inch (2.5 cm)
  • Mild side effects persist for more than three days
  • Side effects reappear after subsiding
  • No relief in swelling or pain even after three days
  • Baby displays loss of appetite or poor sleep after vaccination
  • The baby has been fussy for more than three days after vaccination

Frequently Asked Questions

1. Is there any mercury in vaccines?

Thimerosal is a mercury-based preservative that has been used in vaccines to prevent the growth of bacteria and fungi. It does not last in the body for long to reach dangerous/harmful levels and only causes swelling or redness at the shot site (9). Several childhood vaccines, such as MMR, chickenpox, and polio vaccines, do not contain the compound.

2. Can vaccines cause autism?

No, vaccines do not cause autism (10). There has been extensive research on the possible link between vaccine ingredients and the development of autism. There is no evidence that a vaccine or its compounds could trigger the onset of autism in babies.

Vaccination helps protect your baby against infectious diseases and illnesses that can be life-threatening or cause disability. Babies may experience some common side effects that seldom cause any discomfort. Severe side effects are very rare and may more commonly occur in babies with comorbidities. In most cases, the benefits of vaccines outweigh the risks of side effects. Discuss the potential side effects of a vaccine with your baby’s healthcare provider to be better prepared at managing them adequately.


MomJunction's articles are written after analyzing the research works of expert authors and institutions. Our references consist of resources established by authorities in their respective fields. You can learn more about the authenticity of the information we present in our editorial policy.
1. What Every Parent Should Know About Immunizations; Stanford Children’s Health
2. Who Should NOT Get Vaccinated with these Vaccines?; CDC
3. Vaccines for People with Health Conditions; U.S. Department of Health and Human Services
4. Immunisation – side effects; Better Health Channel
5. Vaccines for your child; Health Service Executive
6. Immunization Reactions; Seattle Children’s Hospital
7. Vaccine Side Effects; U.S. Department of Health and Human Services
8. Medical Management of Vaccine Reactions in Children and Teen in a Community Setting; Immunization Action Coalition
9. Thimerosal and Vaccines; CDC
10. Autism and Vaccines; CDC
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Dr. Priya Thomas

Dr. Priya Thomas is a board-certified pediatrician practicing in Alpharetta, Georgia. She grew up in Kerala and completed her undergraduate degree at Georgia State University and medical education at Medical College of Georgia. Dr. Thomas has a special interest in mental health of children and she recently completed a mini fellowship in mental health. She lives with her husband and... more

Dr Bisny T. Joseph

Dr. Bisny T. Joseph is a Georgian Board-certified physician. She has completed her professional graduate degree as a medical doctor from Tbilisi State Medical University, Georgia. She has 3+ years of experience in various sectors of medical affairs as a physician, medical reviewer, medical writer, health coach, and Q&A expert. Her interest in digital medical education and patient education made... more