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Delayed Injection-Site Reactions After COVID-19 Vaccines

While we have gotten used to the fact that vaccines can cause immediate reactions, like pain, fever, and allergic reactions, some are surprised when they cause delayed reactions.

Some folks are describing the delayed large local reaction seen after their vaccine as COVID arm.

Especially when the delayed reaction is a large local reaction that some folks are describing as “COVID arm…”

What Are Delayed Injection-Site Reactions?

These delayed-injection site reactions might occur about eight days (range from 4 to 11 days) after a dose of COVID-19 vaccine, causing redness, inflammation, itchiness, and pain.

“Delayed injection-site reactions (those with onset on or after day 8) were noted in 244 participants (0.8%) after the first dose and in 68 participants (0.2%) after the second dose. Reactions were characterized by erythema, induration, and tenderness, and they resolved over the following 4 to 5 days.”

Efficacy and Safety of the mRNA-1273 SARS-CoV-2 Vaccine

Fortunately, these delayed-injection site reactions go away fairly quickly without any specific treatment.

“People with only a delayed-onset local reaction (e.g., erythema, induration, pruritus) around the injection site area after the first vaccine dose do not have a contraindication or precaution to the second dose. These individuals should receive the second dose using the same vaccine product as the first dose at the recommended interval, preferably in the opposite arm.”

Interim Clinical Considerations for Use of COVID-19 Vaccines Currently Authorized in the United States

And these delayed-injection site reactions are not a reason to avoid another dose of COVID-19 vaccine if it is needed. In fact, many patients do not have the same type of large local reaction when they get their second dose!

Most importantly, having a delayed type reaction doesn’t make it more likely that you will have an anaphylactic reaction the next time you get the vaccine.

What Causes Delayed Injection-Site Reactions?

What causes the reaction?

“Type IV hypersensitivity or delayed hypersensitivity reaction occurs 48–72 hours after exposure to the allergen. This reaction does not involve antibodies. Instead, eosinophils, monocytes, or lymphocytes called T cells are activated by the antigen. The helper CD4+ T cells initially recognise the antigen, releasing cytokines that activate the immune system with killer CD8+ T cells to destroy the target cells on contact, and macrophages to wall off the antigen and prevent further damage.”

Allergies explained

It is thought to be a delayed-type or T-cell–mediated, type IV hypersensitivity reaction that is triggered by something in the vaccine, typically an antibiotic, adjuvant, or preservative.

These delayed large local reactions likely don't just occur after the Moderna COVID-19 vaccine.
These delayed large local reactions likely don’t just occur after the Moderna COVID-19 vaccine.

Again, as it is just a local reaction, when this type of reaction happens with a vaccine, whether it is the COVID-19 vaccine, flu vaccine, or DTaP, etc., it is not considered a contraindication to another dose.

Is there any treatment for these large local reactions?

If necessary, treatment can include ice or cool compresses, antihistamines (Zyrtec), medium to high potency topical steroids, and/or pain relievers.

“Large local vaccine reactions secondary to T–cell infiltration are often associated with prolonged and very effective immunity. Delayed reactions are often self-limiting conditions that do not contraindicate administration of future doses (eg, booster doses) of the same vaccine.”

Vaccine-associated hypersensitivity

And although absence of a delayed-injection site reaction doesn’t mean your vaccine won’t be effective, if you did have one of these large local reactions, you can probably be confident that your vaccine worked!

Also, you can and should report your large local reaction to VAERS and during your v-safe health check-in, even though it is a known reaction.

More on Delayed Injection-Site Reactions

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