Do mRNA COVID vaccines have a similar >3-day symptom rate?

The short version: the retrieved studies do not give a clean answer for mRNA vaccines, but the pattern is that most symptoms resolve within a few days, and the evidence for symptoms lasting past 3 days is thin.

The one study here that directly reports symptom duration after mRNA vaccines is from Japan, looking at delayed injection site reactions after the Moderna shot [3]. Among 1,098 recipients, about 7 in 100 had a delayed reaction (redness starting 2 or more days after the shot). For those who had it after the first dose, the redness lasted a median of 7 days; after the second dose, a median of 5 days [3]. That is a specific skin reaction, not general symptoms like fever or fatigue.

A UK study of people with long COVID found that vaccination (including mRNA) was linked to a roughly 13% drop in the odds of having long COVID symptoms, but that is about pre-existing illness, not new symptoms after the shot [2]. A study of children with arthritis found that tiredness, headache, and fever after the Pfizer shot resolved within 1–2 days [4]. A study of Italian healthcare workers found that fever, fatigue, and headache were more common after the second dose than the first, but did not report how long they lasted [5].

What is missing: no study here tracks a general population after an mRNA shot and reports what fraction still has symptoms past day 3. The delayed injection site reaction study gives a duration for one specific symptom, but that is not the same as general symptoms. The 3 in 100 figure from the previous answer came from a different vaccine type (Covaxin/Covishield) in India, not from mRNA vaccines [1].

My call: the evidence does not support a firm rate for symptoms lasting past 3 days after mRNA COVID vaccines. The available data suggests most symptoms resolve within a few days, but nobody has measured this properly in a general population. Confidence: low.