COVID-19 symptoms and the Delta variant
With the Delta variant now driving surges of COVID-19 cases worldwide, researchers are examining whether it's causing different symptoms from earlier variants and how it's experienced by vaccinated and unvaccinated people.
Severe breakthrough infections of COVID-19 remain uncommon, but a growing number of people in the US are testing positive after being fully vaccinated, with some describing symptoms unlike those that marked earlier COVID waves.
Months of research and real-world evidence previously suggested most fully vaccinated people would face similar but milder versions of the same disease sickening unvaccinated people.
One recent study led by the CDC's Mark Thompson, closely following essential and frontline workers through April, found the risk of symptoms and duration of illness was much lower among most vaccinated participants with breakthrough cases.
Studies show that runny nose, headache, sneezing, sore throat, and loss of smell are the top five symptoms for fully vaccinated people who contracted COVID.
Missing from that top-five list was coughing or shortness of breath, which were among the most frequently reported signs of COVID-19 early in the pandemic, before vaccines were available. A runny nose and sneezing were not commonly reported in initial cases.
However, not all recent studies of the Delta variant have turned up differences between cases in vaccinated and unvaccinated people.
The CDC's investigation of the outbreak in Massachusetts, which led to the discovery that fully vaccinated people with COVID had as much virus in their nose as the unvaccinated, documented "cough, headache, sore throat, myalgia, and fever" as the most common symptoms among 274 cases of fully vaccinated people who reported symptoms.
In the U.K., health authorities recently said the prevalence of "classic" symptoms — fever, cough, fatigue, and headache — among all cases of COVID-19 actually "appears to have increased in June and July 2021," when the Delta variant began to dominate most cases there.
"In terms of the symptoms that we see that are different between vaccinated versus unvaccinated individuals, the symptoms really remained the same," says Dr. Jack O'Horo, a critical care and infectious diseases specialist at the Mayo Clinic.
"We're still looking at initially cold-type symptoms like cough and fever. And people who have more severe infections, pneumonia-type infection symptoms," said O'Horo.