COVID-19 symptoms differed between Omicron and Delta variants, U.K. study found

The top symptoms of the Omicron COVID-19 variant may differ from symptoms that were common at the start of the pandemic. Omicron may also be less severe than the Delta variant, a study out of the U.K. found.

People with Omicron often report sore throat and a hoarse voice, which were not as prevalent in Delta cases, a Zoe Health Study found. This is true for vaccinated and unvaccinated patients.

People who contracted the Omicron variant were less likely to be hospitalized compared to those with the Delta variant, Zoe Health said in a press release about the study. Symptoms also lasted for shorter periods – an average of 6.87 days, compared to 8.89 days.

Earlier COVID-19 variants often caused people to lose their sense of smell. The study found that symptom appeared in less than 20% of cases and often days after the first symptoms began. Other serious symptoms that used to be prevalent – like fever, headaches, brain fog and eye soreness – are less prevalent in Omicron cases. However, they can still occur.

The Zoe Health Study, which was supported by grants from the U.K. Government Department of Health and Social Care, tested people in the U.K. who were vaccinated. They tested participants between June 1 and November 27, 2021 – when the Delta variant was dominant – and between Dec. 20, 2021 to Jan. 17, 2022 – when the Omicron variant dominated.

The study collected 62,002 positive tests and looked at those patients' symptoms. In addition to a difference in the length and types of symptoms between the two variants, researchers said Omicron is found far less frequently in the lower respiratory tract. This is where infection can cause more severe symptoms, potentially sending people to the hospital.

They also found Omicron symptoms do not last as long in vaccinated people.

Delta is better at infecting lung cells than Omicron, the study found. And while Omicron appears to be much more transmissible than previous variants, this variant affects fewer organs than Delta, other studies have found, according to Zoe Health.

The Omicron subvariant that was prevalent at the end of 2021 and the start of 2022 was labeled BA.1. There are now Omicron subvariants, labeled BA.4 and BA.5 that appear to be causing a loss of sense of smell or taste again, Dr. Celine Gounder told CBS News.

A similar study from Imperial College London also found that there was lower reporting of loss of sense of smell and taste for the Omicron variant. However, the study which is yet to be peer-reviewed, found there was higher reporting of cold-like and influenza-like symptoms.

The study used data from REACT-1, a widespread survey in the U.K. that collected at-home COVID-19 tests from about 1.5 million participants between 2020 to 2022, and analyzed how symptoms differed between variants and subvariants.

While it is perceived that newer variants like Omicron are milder, Omicron subvariant BA.2 was associated with reporting more symptoms, with greater disruption to daily activities, than the Omicron subvariant BA.1.