Data suggests the Delta variant might cause more severe illness than previous strains in unvaccinated persons. People infected with the Delta variant are more likely to be hospitalized than patients infected with the Alpha or original virus strains. Vaccinated people are either asymptomatic or have very mild common cold symptoms such as cough, fever or headache, with the addition of loss of smell.
https://www.cdc.gov/coronavirus/2019-ncov/variants/delta-variant.html