Question: I’m vaccinated, and curious to know– what are the common symptoms of breakthrough infection?  

Answer: We have the makings of an answer to your question thanks to the observational COVID Symptoms Study.  Earlier this month, study researchers published an observational, matched case-control study in Lancet Infectious Diseases that addresses this very topic, Risk factors and disease profile of post-vaccination SARS-CoV-2 infection in UK users of the COVID Symptom Study app.  Based on data collected between early December 2020 and early July 2021, authors found that “Almost all symptoms were reported less frequently in infected vaccinated individuals than in infected unvaccinated individuals, and vaccinated participants were more likely to be completely asymptomatic.”  Compared to the unvaccinated, fully vaccinated individuals were also less likely to have 5+ symptoms and less likely to have symptoms lasting more than 28 days.  Among fully vaccinated individuals who experienced a breakthrough infection, the most common symptoms were as follows: fever (62%); fatigue (44%); runny nose (43%); headache (42%); sneezing (39%); sore throat (29%); cough (28%); loss of smell (21%); hoarse voice (21%); and dizziness/lightheadedness (20%).  Interestingly, only one symptom was more common among partially vaccinated individuals compared with unvaccinated individuals– sneezing! (Figure 1)

Figure 1. Odds of COVID Symptoms by Vaccination Status (from Lancet) (among those who become infected, partially and fully vaccinated individuals have lower odds of experiencing nearly all symptoms compared with unvaccinated)