Post-COVID-19 vaccination side effects cannot be clearly differentiated from the early symptoms of the virus, according to new findings led by researchers at King’s College London and published last week in the eClinical Medicine journal.

Researchers who conducted the study, titled “Disentangling post-vaccination symptoms from early COVID-19” noted that “some individuals experience systemic symptoms post-vaccination, which overlap with COVID-19 symptoms.”

Scientists sought to differentiate the two by comparing early post-vaccination symptoms in individuals who subsequently tested positive or negative for SARS-CoV-2, using data from the COVID Symptom Study (CSS) app, formerly the COVID Symptom Tracker, an epidemiological research mobile app developed in the United Kingdom.