Omicron symptoms less severe than Delta, study finds

Omicron symptoms do not last as long in those who have been vaccinated, researchers say

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People who have Omicron are more likely to have a sore throat and less likely to lose their smell compared to Delta, a new study has found.

The research indicates people are also less likely to be admitted to hospital with the current dominant variant and that symptoms do not last as long in those who have been vaccinated as they do with Delta (6.87 days compared with 8.89 days).

The findings support previous studies that suggest the incubation time and period of infectiousness for Omicron is shorter than for previous coronavirus variants.

The research says the biggest difference was in the loss of sense of smell, which appeared in 52.7 per cent of Delta cases, and showed up in fewer than 20 per cent of Omicron cases.

The two Covid-19 symptoms that were consistently prevalent in both variants, regardless of vaccination, were a sore throat and hoarse voice.

Researchers found some of the more debilitating symptoms — such as brain fog, eye burning, dizziness, fever and headaches — were significantly less prevalent in Omicron cases.

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“We observe a different clinical presentation of symptoms in those infected with Omicron compared to Delta," said Dr Cristina Menni from King’s College London.

“As we are moving even further away from the average patient having UK government ‘core’ symptoms — that is fever, persistent cough, loss of smell — our results point to a different selection of symptoms that may indicate infection.

“To protect others, it is still important to isolate for five days as soon as you see any symptoms.”

Prof Ana Valdes, an honorary professor at King’s College London, said: “Although there is still a wide range of duration and severity of symptoms with Omicron, for vaccinated individuals we find on average a shorter duration of symptoms.

“This suggests that the incubation time and period of infectiousness for Omicron may also be shorter.”

Researchers from King’s College London and Zoe studied the symptoms of 62,002 vaccinated UK participants from the Zoe Covid Study App who tested positive between June 1 last year and November 27, 2021, when Delta was dominant, and December 22, 2021, to January 17 this year when Omicron was dominant.

The study will be presented at the European Congress of Clinical Microbiology and Infectious Diseases this month in Lisbon.