The delta variant is the most-contagious mutation of the novel coronavirus and represents more than 50% of all new U.S. cases as of July.
Recovery from a previous COVID infection provides only minimal antibody protection from variants.
Studies have found efficacy rates of the two-dose Pfizer vaccine against the delta variant range from 64% in Israel, known for doing huge amounts of testing, to 79% in Scotland and 88% across the U.K.
It requires only a few seconds for delta to spread, and its patients, who generally are younger, are often sicker by the time they make it to the hospital. Unlike the original strain, which caused predominant symptoms of fever, cough, and loss of taste and smell, common symptoms of the delta variant — which carries twice the risk of hospitalization — are a headache, sore throat, runny nose and fever.
Pictured: electron microscope image of COVID-19 (yellow) emerging from the surface of a patient's cells (blue/pink)