Lumps (knots) in a baby’s leg after vaccination are common side effects. Let’s take a look at why this happens, other common side effects, how to mitigate them, and when to call the doctor.
knot in leg after vaccinePin

The information in this article is provided by Pediatrician Leah Alexander. The purpose is to provide examples and knowledge to help parents dig deeper into their baby’s situation, not to offer a complete picture or a possible diagnosis.

Mom’s Question:

My baby has a small knot in his leg after the vaccine; it showed up after his 4-month shots. It has been 2 weeks since he had them (vaccines), and the knot is still there. Why is this, and is it common? Should I take him to the doctor?

What other vaccination side effects are there? Is there something else I should look for?

Easy Baby Life:

Vaccination Side Effects in Babies, Mitigation and Red Flags

A Knot in Leg After Vaccine – Normal?

Let’s first talk about the specific side effect you are worried about; a knot in your baby’s leg after the vaccination.

The majority of vaccines are injected into a muscle. Under the age of two, the anterior thigh is the most common location. Sometimes, an area of inflammation develops within the muscle that feels like a “lump” or “knot” within two to three days. It is not painful and goes unnoticed unless the area is massaged. Skin redness and swelling are absent.

Clinically, this reaction is commonly seen following a DTaP or PCV vaccine. It is normal, expected, and usually self-resolves over the course of a few weeks but can remain for months.

Applying a warm compress and massaging the “lump” can help reduce the timeframe of its resolution.

Other Common Side Effects After Vaccination Shots

After vaccination, a knot or lump in the leg is just one of the possible side effects.

As part of the immune-boosting process, it is possible for infants and toddlers to experience mild side effects from the vaccines they receive. Except for live vaccines, most reactions self-resolve 24 to 48 hours after the time of administration.

Expected side effects

  • Fever no higher than 101.5 degrees F
  • Mild fussiness
  • Taking longer naps
  • Soreness at the site of injection

As stated above, your baby may be extra sleepy after the shots. One of my babies got very sleepy after her shots and actually slept through the night for a change! :-)

I remember that I even joked with her doctor that I wanted my baby to have shots at least once per week – that was the only time she slept well at night…

Our youngest wasn’t at all as affected. It is very individual.

MMR and VAR vaccine side effects

The reactions following the MMR and varicella vaccines differ because they are live vaccines.  They are also administered into the subcutaneous fat instead of muscle. 

Symptoms may not develop until one to two weeks post-administration and can include a mild rash (source).

The rash following the MMR vaccination may cover your child from head to toe or just present at the torso. It will look like small red bumps and should self-resolve within one week. The rash is not contagious and should not bother your child.

The VAR vaccination can result in a rash that looks like mild chickenpox. This, too, should not bother your child.

Rotavirus vaccine side effects

Following the oral live rotavirus vaccine, fever, vomiting, and diarrhea are rare but possible (source).  If a vomiting episode occurs at the time of vaccine administration, the dose does not need to be re-administered.

Some studies have shown a small increased risk of intussusception (a type of bowel blockage) within a week after the first or second dose of the rotavirus vaccine. The additional risk is estimated to range from about 1 in 20,000 to 1 in 100,000 US infants who get the rotavirus vaccine, so it is not something to worry about. However, if your baby appears to have stomach pain, severe crying, vomiting, and possibly blood in their stools, you should call a doctor immediately or take your baby to the hospital.

How to mitigate the vaccination side effects in babies

If your infant or toddler seems uncomfortable or has a fever after receiving a vaccine, acetaminophen is most commonly recommended (source)

If there is tenderness at the site of vaccine administration, warm compresses, and massages can be helpful. Some relief of symptoms should be evident after using these remedies.  If not, you should call your doctor.

Vaccination Side Effects – When to Call the Doctor?

Abnormal symptoms following a vaccine include the following (source):

  • A seizure that occurs with or without fever
  • A fever that lasts more than 48 hours or is higher than 101.5 degrees F (38.5 C)
  • Local swelling, redness, and pain after 24 hours
  • A reduction in feeding
  • Lethargy or decreased wakefulness
  • Signs of an allergic reaction such as hives, facial swelling, and decreased responsiveness

If any of these symptoms develop, emergency medical intervention is warranted.

One side effect of the DtaP and the MMR that was earlier feared was autism. This connection, however, is by now quite well researched and highly disputed and not something to fear.

If you are worried about your baby’s psychological development (although unrelated to vaccines), you can read about signs of autism in babies and toddlers here.

I hope this helps,

So, how about all other babies..? Has anyone found a knot in the leg after the vaccine or any other side effects worth noting? Share by leaving a comment!

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This Post Has 20 Comments

  1. Barakat

    My baby of two months collect injection about three weeks now and swellen up red am worried

  2. Mahi

    My baby is also having knot like on her leg how will it go almost 2month not going still

    1. Paula @ EasyBabyLife

      Hi Mahi, these knots can remain for several months, but will disappear eventually.

  3. ann

    This article has been extremely helpful to me. Thank you.

  4. Peppe


    When my daughter got her 4 month shots her little legs lumped up really good she will now be 6 months old and still has a lump and an indention where one of her shots was placed.

    I’m getting a little worried

    Thank you

    1. Paula @ EasyBabyLife

      As I wrote above, it can take a long time for the lump to disappear, months even. But if you are not completely sure that the lump is related to the vaccine or if it starts changing in any way (unless diminishing), then let a doctor have a look at it.

  5. Chrissy

    My daughter is 4yrs old and received the shots in her legs. Its been a week now. I’m worried because she also has sickle cell anemia ss. These lumps are huge and warm. She’s also complaining about them hurting. I’ve been applying warmth packs and giving pain meds. What should I do?

    1. Shannon

      I would take her to the ER or doc i wouldn’t chance anything could be sign of a infection.

  6. Alina

    My daughter has no lump, but she developed a rash on both legs after her 2 mos and 4 mos immunizations. She was sleepy too!

  7. Tanya

    My 4 month old son also has small red dots on his legs after receiving vaccinations. From what I have read, it’s from the MMR vaccine. Your child can also have these red dots on their legs after they have received the varicella (chicken pox) vaccine.

  8. Ann

    My daughter got her 1 year shots about a week ago and today I changed her and she has little red bumps kind of like a rash bumps on her legs and arms. My doctor told me she would get a rash and maybe a fever about 10 days after the shot, so I guess it is all normal and nothing to worry about. :-)

  9. Paula @easybabylife

    Hi Sallina,
    Sore lumps after vaccination are common, but if it’s been a month since he got his shot, then maybe you should check back with his health care provider. Sore lumps can last up to a month, but it might be good to check that he hasn’t had a reaction to the vaccine. Is he well otherwise?

  10. toucan

    my son is almost 3 and he has a lump where he received his vaccinations when he was a baby. He scratches this area, sometimes until it bleeds. It itch seems to bother him off and on. It is possible it will still go away or should i have this checked?

    1. Nathaniel A Haynes

      WTH that is some weird stuff

    2. Martina

      My son is almost 2 and he is going through this same thing. I’m soo worried and his pediatrician says it will go by itself.

    3. Christine

      I just seen your post about lump post vaccines. What was the outcome after? Thanks

  11. Briana Daniele Morris

    My son just got his 6 month shots 2 days ago and his leg is swollen and red and has a knot right under it. The nurse gave him all 4 shots on the same leg.. Now he won’t really even move it and definiatly won’t let me touch it. Should I take him back to the Dr.?

    1. nichole

      My son got his 1yr shots and has lumps from the shots on both legs hes never done that with other shots

    2. Krystal

      You should have them even out there shots 2 in each instead of 4 in 1 poor lil guy

    3. Michaela

      OMG! I would have lost my mind!! I’m so sorry that poor baby, that breaks my heart. I’d definitely take him back and complain about that nurse cause that just insane!!