Duration of symptoms shorter with omicron, app-based data show
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Vaccinated people who were subsequently infected with SARS-CoV-2 experienced a shorter duration of symptoms if they were infected with the omicron variant vs. the delta variant, mobile-app based data showed.
They also experienced less severe symptoms and a lower risk for hospitalization, according to a study published in The Lancet that will also be presented at the European Congress of Clinical Microbiology & Infectious Diseases this month.
“Early reports suggested infection with omicron was less severe than with previous variants,” Cristina Menni, PhD, a professor at King’s College London, and colleagues wrote, although they noted that “no detailed published reports have investigated symptom prevalence and acute symptom duration, and how these compare to the delta variant.”
“We aimed to quantify the differences in symptoms, risk of hospital admission, and duration following infection with the omicron or delta variants among people vaccinated (two or three doses) in a large community cohort from the U.K.,” they wrote.
The study enrolled people aged 16 to 99 years who had received at least two doses of any SARS-CoV-2 vaccine, had a BMI between 15 and 55 kg/m2, were symptomatic for COVID-19 and reported these symptoms through an app associated with the ZOE COVID Study, and logged a positive symptomatic PCR or lateral flow result for SARS-CoV-2 during the study period.
Between June 1, 2021, and Jan. 17, 2022, Menni and colleagues identified 63,002 participants who tested positive for SARS-CoV-2 and reported symptoms. They matched the patients from the delta and omicron waves in the U.K. in a 1:1 ratio for age, sex and vaccination dose.
The researchers found that people infected during the omicron wave were 2.5 times as likely to recover within 1 week of symptom onset compared with those who were infected during the delta wave.
Patients with omicron were also 25% less likely to be admitted to the hospital than patients with delta (1.9% vs. 2.6%), and their duration of acute symptoms was shorter during omicron than delta (mean of 6.9 days vs. 8.9 days).
According to the researchers, the difference was less prevalent among study participants who had received only two doses of vaccine (9.6 days vs. 8.3 days) and more prevalent among individuals who had received three doses of vaccine (7.7 days vs. 4.4 days).
In an accompanying comment, Linda Houhamdi, and Pierre-Edouard Fournier, MD, PhD, both of Aix-Marseille University and Public Assistance-Hospital of Marseille in France, wrote that using mobile apps to monitor diseases is “highly valuable” and can be easily implemented across many populations.
“Understanding both the characteristics of COVID-19 and the dynamics of its causative variants constitutes a crucial milestone in preventing transmission and reducing infection, hospital admission and death,” they wrote. “Large-scale tracking tools that use simple and accessible devices and enable rapid and widespread analyses are extremely desirable.”
References:
Houhamdi L, et al. Lancet. 2022;doi:10.1016/S0140-6736(22)00453-6.
Menni C, et al. Lancet. 2022;doi:10.1016/S0140-6736(22)00327-0.
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