April 8, 2022
The COVID-19 symptoms caused by the Omicron variant tend to last about two days shorter than symptoms from the Delta variant, according to a new study published in The Lancet.
In addition, among fully vaccinated people, a symptomatic Omicron infection was 25% less likely to result in a hospital admission as compared with Delta.
“The shorter presentation of symptoms suggests (pending confirmation from viral load studies) that the period of infectiousness might be shorter, which would in turn impact workplace health policies and public health guidance,” the study authors wrote.
Researchers from King’s College London analyzed data from the ZOE COVID app, which collects data on self-reported symptoms. In this study, the researchers focused on vaccinated people who kept a smartphone log of their COVID-19 symptoms after breakthrough infections developed.
The research team analyzed data from June through November 2021, when the Delta variant accounted for more than 70% of cases, and from December through mid-January, when Omicron accounted for more than 70% of cases. The patients — about 5,000 in each group — were matched and compared with a person of the same age, sex and vaccination dose in the other group.
Omicron’s shorter symptom duration was more prominent among people with three vaccine doses. Symptoms lasted about 7.7 days during the Delta-dominant months and 4.4 days during the Omicron-dominant months, meaning a difference of 3.3 days.
Among those with two vaccine doses, symptoms from Delta lasted for 9.6 days and symptoms from Omicron lasted for 8.3 days, making a difference of 1.3 days.
The types of symptoms also varied. Loss of smell was more common during the Delta period, and sore throat and hoarse voice were more common during the Omicron period. Both coronavirus variants had common symptoms such as runny nose, headache and sneezing, but debilitating symptoms such as brain fog, dizziness and fever were less prevalent in Omicron cases.
In addition, there was a lower rate of hospital admission during the Omicron period than during the Delta period, the study authors wrote, potentially due to less involvement of the lower respiratory tract in Omicron infections.
“The clinical symptoms associated with symptomatic infection by the SARS-CoV-2 omicron variant are different, milder, and of shorter duration than those presented by the delta variant among vaccinated individuals,” the study authors wrote. “However, this might not be the case in unvaccinated individuals.”