A large study published in The Lancet confirms that the symptoms induced by the Omicron variant are less severe, last less long and differ from those caused by the Delta variant in people who have received two or three doses of the vaccine against COVID-19.
These findings come from a survey of vaccinated Britons who tested positive for COVID-19 and reported their symptoms daily on a mobile app. The study authors, researchers from King’s College London, compared the symptoms of 5,000 people who were infected between 1er June and November 27, 2021 — presumably by the Delta variant, which was the most prevalent during this period — to those of 5,000 subjects who contracted COVID-19 between December 20, 2021 and January 17, 2022, the period when Omicron is imposed as the dominant variant.
The more intense Delta variant
The researchers noticed that loss of smell, which was a common symptom during the early waves of the pandemic, was much less so in people with Omicron-induced infection. Only 17% of participants infected with Omicron were affected, compared to 53% of those who contracted the Delta variant. According to a statistical model designed by the researchers, people who are victims of Omicron would be 83% less likely to develop a loss of smell. Other symptoms, such as sneezing, eye irritation, altered sense of smell, mental fog, dizziness, fever, and headache were also significantly less common during the Omicron-dominance period. compared to that of the Delta.
On the other hand, the two symptoms which appeared to be the most common caused by the Omicron variant were sore throat and hoarseness of the voice. According to a statistical analysis, people infected with Omicron have a 55% higher risk of suffering from sore throats. In the study, they were 24% more likely to experience cracking in their voices, but half as likely to develop fever and a persistent cough.
The probability of hospitalization was 25% less with Omicron than with Delta: 1.9% of patients infected with Omicron were admitted to hospital, compared to 2.6% of patients during the Delta wave. This trend is supported by previous observations made in South Africa and South Korea.
The average duration of symptoms was also two days shorter in people who developed COVID-19 during the Omicron wave than previously, when the Delta variant was dominant. This difference was even greater (3.3 days) in people who received three doses of the vaccine, i.e. an average duration of 7.7 days for the Delta variant compared to 4.4 days for Omicron. In people who received only two doses, the difference was only 1.3 days, giving an average duration of 9.6 days for the Delta variant versus 8.3 days for Omicron.
The researchers were able to estimate that people infected during the Omicron period were 2.5 times more likely to see their symptoms disappear within seven days of their onset than those struck by the Delta variant.
“Less serious” if vaccinated
The study authors state that these latest findings, which indicate a shorter symptomatic window and faster resolution of symptoms with Omicron, suggest that the Omicron variant would generally induce “less severe infection than previous variants in vaccinated populations.” “.
These observations are consistent with analyzes in vitro having shown that the Omicron variant replicates faster than other SARS-CoV-2 variants in the bronchi, but does so less efficiently in the lung parenchyma [c’est-à-dire la couche de tissu dans laquelle a lieu l’échange gazeux entre le sang et l’air]. This variant appears to enter cells via a different route than the other variants,” the researchers write.
The latter admit that they were unable to compare the symptoms, their duration and the risk of hospitalization between the Omicron and Delta variants in unvaccinated people, since the vast majority of study participants were vaccinated.