New UK study confirms reduced severity of Omicron variant of Covid-19

Researchers in the UK on Friday reported that the Omicron variant of SARS-COV-2 (COVID-19) has a lower risk of hospitalisation and a shorter duration in the vaccinated population than previous variants, including Delta.

King's College London and ZOE COVID Study scientists studied the symptoms of 62,002 vaccinated individuals to conclude that those infected with Omicron are more likely to have a sore throat and less likely to experience loss of smell compared to Delta.

The findings, published in The Lancet' this week, show the duration of symptoms were also significantly shorter for Omicron compared to the Delta variant 6.87 days versus 8.89 days respectively and participants were less likely to be hospitalised.

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, said Professor Ana Valdes, Honorary Professor at King's College London.

The researchers note that symptoms associated with an Omicron infection have less involvement of the lungs and do not last as long in vaccinated people.

The most striking difference between variants was the difference in loss of sense of smell, a common symptom of earlier variants appearing in 52.7 per cent of Delta cases, only appears in under 20 per cent of Omicron cases and often days later.

The two symptoms that were consistently more prevalent among Omicron than Delta cases, regardless of vaccination status, were a sore throat and hoarse voice. Moreover, many debilitating symptoms, such as brain fog, eye burning, dizziness, fever, and headaches, though still occurring, were all significantly less prevalent in Omicron cases.

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 i.e. 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, she said.

The UK's National Health Service (NHS) had added further symptoms to watch out for, including shortness of breath; feeling tired or exhausted; aching body; headache; sore throat; blocked or runny nose; loss of appetite; diarrhoea; and feeling sick or being sick.

Earlier reports had indicated that the Omicron variant was significantly less severe than the previous dominant COVID variants, with lower rates of hospital admission. However, the researchers say their study is larger, population based and the most detailed so far.

It included samples from the ZOE COVID Study App who tested positive between June 2021 and November 2021, when Delta was dominant, and from December 2021 to January 2022 when Omicron was dominant in the UK.

Tim Spector, Lead Scientist on the ZOE COVID Study and Professor from King's College London, described the latest findings as an amazing scientific feat that offers conclusive answers to key clinical questions on symptom and severity.