Omicron symptoms are different from Delta variant, study finds

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A new observational study out of the U.K. has found that those who contract the Omicron variant of COVID-19 experience different symptoms that are usually less severe and last shorter than those who are infected with the Delta variant.

According to the ZOE COVID Study, which tracks self-recorded symptoms from participants using a smartphone app, those who contract Omicron are less likely to be admitted to hospital and lose their sense of smell than people with Delta.

The study also found that some of the "more debilitating symptoms" of COVID-19, including brain fog, eye burning, dizziness, fever and headaches, were also less prevalent in Omicron cases. Participants infected with Omicron were also less likely to report suffering from a cough, according to the study.

"The prevalence of symptoms that characterise an omicron infection differs from those of the Delta SARS-CoV-2 variant, apparently with less involvement of the lower respiratory tract and reduced probability of hospital admission," the study's authors wrote.

However, researchers report two symptoms that were "consistently prevalent" in both variants, regardless of one's vaccination status -- a sore throat and hoarse voice.

The findings were published Thursday in peer-reviewed medical journal The Lancet, and will be presented at the European Congress of Clinical Microbiology and Infectious Diseases later this month.

Researchers from King's College London studied the symptoms of 63,002 vaccinated U.K. participants who tested positive for COVID-19 between June 1, 2021 and Nov. 27, 2021, when the Delta variant was the dominant strain circulating, as well as Dec. 22, 2021 to Jan. 17, 2022, when Omicron became dominant.

Patients from each group were matched and compared with a person of the same age, sex, and vaccination dose in the other group.

The study did not compare symptoms, hospital admissions or duration of infection by the two variants in unvaccinated individuals.

According to the findings, the greatest difference in symptoms between the two variants is the loss of smell, which appeared in 52.7 per cent of Delta cases compared to less than 20 per cent of Omicron cases.

Researchers found symptoms lasted on average 6.9 days when infected with Omicron, compared to 8.9 days for those who contracted the Delta variant.

Omicron's shorter symptom duration was also more pronounced in those with three vaccine doses, highlighting the importance of booster shots, researchers say.

"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's authors wrote.

In addition, the study reported that hospital admissions were 25 per cent lower during the period when Omicron was dominant.

The study supports previous findings that show the Omicron variant to be milder for vaccinated populations in terms of severity, despite it being more transmissible than the Delta variant.

According to the Public Health Agency of Canada, common symptoms of COVID-19 include a runny nose, headache, new or worsening cough, shortness of breath, fever, sneezing, fatigue, body aches and a loss of smell or taste.

However, the agency notes these symptoms can vary from person to person in different age groups, as well as depending on the variant they are infected with.

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