A new study published in PLoS One investigated whether microRNA (miR)-451a levels in serum extracellular vesicles (EVs) correlate to local symptoms at the vaccination site, such as pain, itching, swelling, and redness. Here, the level of several immune-regulatory miRNAs were determined in serum EVs. Using the immune-regulatory miRNA levels of miR-22, miR-29a, miR-451a, and miR-107, a normalized miRNA level for each healthy donor were calculated. It was found that miR-451a levels in serum EVs inversely correlated to the number of symptoms after vaccination. Additionally, the normalized miRNA levels significantly correlated to the number of local symptoms post vaccination. The results indicated that immune-regulatory miRNA levels in serum EVs can be used as biomarkers to assess local symptoms after influenza vaccination.