How to Identify Signs of an Infection from a Vaccine 

With flu season upon us and the decision to vaccinate or not, I decided to share our story with Harv’s recent scare.

Before I share my knowledge and information, I’d like to be clear about 2 things. One I vaccinate all my kids and my unwilling husband. Ok I don’t personally ha no one wants that, but I believe in their value. I believe in vaccinations only because I’ve had to be a hermit and deal with a non traditional schedule and it’s scary and not fun. Second, this is not a post about helping you decide whether to vaccinate or not or on which schedule. Please be respectful of others and their beliefs in any commentary.

A few weeks ago Harvey went in for his 15 month check up and as normal, he’d receive one scheduled vaccine (Pentacel – diphtheria, haemophilus influenzae type B, pertussis, polio, and tetanus) and the flu vaccine. To our surprise, Harv took them like a champ, no tears or crying. Honest, there wasn’t even a flinch, which was surprising because he got one after another. Typically, two nurses will do them at once. So I scooped him up (Caleb was the holder, thanks Love) and off we went for home.

As with any vaccine, we expected the possibility of a low fever, maybe a little redness, or a little swelling and a lot of crankiness, but also always on the lookout for an allergic reaction. We made it through the evening without any concerns, so I was pretty thrilled at this point. No crying and healthy baby? That’s a win.

Fast forward just over twenty four hours. I went to change his diaper and I notice his left thigh looked slightly incredibly larger than the right. At this point, there was no redness, no fever, no hives, and he was running around stealing Jack’s toys, so it was triaged as ‘keep an eye on it’.

This does not look like a sick baby.
This does not look like a sick baby.
As Saturday night turned to Sunday morning, a high fever struck so it was decided to head to urgent care at this point. Thankfully our clinic has Saturday and Sunday urgent care hours.

With Caleb at work, I packed up Jack and Harv and we headed in. Luckily our normal pediatrician was the attending on call Doc for the weekend, so he knew us and the situation. He said it could be two things: an infection or an allergic reaction. Typically though, an allergic reaction shows up as hives, but not always.

We got an apology and a prescription for 10 days of antibiotics to “test” if it was an infection. If the antibiotics started to reduce the symptoms in a few days, we’d conclude it was an infection, if the antibiotics didn’t work, we’d assume an allergy and that would bring another whole set of problems and concerns.

The result?

An infection.

Ick. Yep. Somewhere in the vaccination process, something wasn’t done properly and when the shot went in, it brought an infection right along with it.

Fast forward to Day 9 of medicine (why does it always end one dose early!?) and a lump is still there. It is different than the large lump from swelling, smaller like a garden pea. Apparently it doesn’t magically disappear at Day 9. So another call to the Doc to find out that it’s a separate issue. I thought it was just the swelling going down. Nope. Trauma to the fat tissue. It has a fancy name that I’ve since forgotten. It could be weeks, even months before it’s gone. Oh joy. At least the swelling and fever are gone.

Let’s get down to the take-aways in all this to really separate “a normal vaccine reaction” to an infection.

The following are considered abnormal and appropriate medical care should be contacted.

  • Swelling. Swelling the size of your fist that’s hard to the touch is not normal. Do keep in mind, it was not painful for Harv when pressed on.
  • A high fever that lasts a few days. Caleb and I don’t usually mess with fevers, we’ve both seen too much. A kid has a high fever and we’re seeing a doctor.
  • Redness. Some reddening is normal, but when the redness spreads through the swelling and well beyond the injection sight, it’s not normal.
  • Hard lump. The real kicker that made it clear it was an infection was that the swelling had a hard spot. I’m not a doctor, so I can’t tell you why. But he did say many many times over, “it’s hard, that worries me”. (Gee thanks, I’m already worried, you can’t be to0.)
  • You know. Yep I fully believe in maternal and paternal instinct. You know when something “just isn’t right”. Trust your gut.


  • Hives. This is NOT about an infection and allergies can show up in different ways, but I’m throwing it out there as a great reminder. Hives are not normal and are a sign of concern.

Thankfully Harvey does not have an allergy to the vaccination, because it is a vaccination he will receive again and since it is a combined vaccination I was worried about future doses. That being said, there is still a note in his chart about the situation for when he will receive a future Tetanus, just in case.

I hope you never find yourself in this situation and yes it could be considered fuel for the non vaccinating families, but I hope you also find value in learning a little more. We all need to work together to take care of all our littles that we love so much.


psst… I’m NOT a doctor. I’m just passing along the information I learned from our family’s experience.

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