Omicron COVID symptoms less severe than Delta variant, study concludes

People who contract the Omicron variant of COVID-19 are likely to experience less severe symptoms than those with Delta, a new study has found.

The research concluded that those with Omicron were less likely to be admitted to hospital and lose their sense of smell than people with Delta.

Symptoms do not tend to last as long in vaccinated individuals with the current dominant variant than in people with Delta, at 6.87 days versus 8.89 days.

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

Research showed that the loss of sense of smell appeared in 52.7% of Delta cases, while it showed up in less than 20% of Omicron cases – marking the biggest difference between the two.

However, the two symptoms that were consistently noted in both variants, regardless of vaccination status, were a sore throat and hoarse voice.

Some of the more debilitating symptoms, including brain fog, eye burning, dizziness, fever and headaches were significantly less prevalent in Omicron cases, according to researchers.

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

“As we are moving even further away from the average patient having UK government ‘core’ symptoms ie 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 self-isolate for five days as soon as you see any symptoms.”

Professor 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.”

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

Findings from the research will be presented at the European Congress of Clinical Microbiology & Infectious Diseases (ECCMID) this month in Lisbon.