Omicron: 3 fewer days of symptoms for those vaccinated with a booster dose

The Omicron variant is less severe than Delta, and the difference is even greater in subjects vaccinated with a booster dose. In these people, symptoms last 4.4 days with Omicron versus 7.7 days with Delta.

It is now commonly accepted that the Omicron variant of SARS-CoV-2 is less severe than its predecessor the variant Delta. One team wanted to quantify things more precisely by evaluating the prevalence of symptomsthe risk of hospitalization and the duration symptoms in vaccinated people. Their results were published on April 7, 2022 in the prestigious journal The Lancet.

Study design

This is a prospective and observational study. The data comes from a application called ZOE COVID in which participants self-reported their test results and symptoms. To be eligible, patients had to:

• be residents of the United Kingdom;
• be between the ages of 16 and 99;
• have received at least two doses of vaccinewhatever the brand;
• be symptomatic;
• have a positive test for SARS-CoV-2.

The primary endpoint of the study was the occurrence of at least one symptom among the 32 available in the application or an admission to hospital within one week after or before the positive result for SARS-CoV-2 . The authors compared data from a period when the Delta variant was predominant with data from a period when the Omicron variant was predominant.

A less severe disease

Between 1^er June 2021 and January 17, 2022, 63,002 participants tested positive for SARS-CoV-2 and reported symptoms in the ZOE COVID app. Two groups were formed and matched on age, sex and number of vaccination doses. In the first group, the tests were positive between 1^er June 2021 and November 27, 2021, at a time when the Delta variant was more than 70% predominant (n=4990). In the second group, the tests were positive between December 20, 2021 and January 17, 2022, at a time when the Omicron variant was more than 70% predominant (n=4990).

Unsurprisingly, loss of sense of smell or the need for infection-related hospitalization was less common in patients infected with Omicron versus those infected with Delta. The sore throat were more common in patients affected by Omicron.

On the other hand, this study highlighted original data: the symptomatic period was shorter in people affected by Omicron (8.3 days) compared to those affected by Delta (9.6 days). This difference was even greater in people who received a booster dose: 4.4 days versus 7.7 days. This means that the period when the patient is contagious is potentially shorter with Omicron than with Delta and depends on the number of doses of vaccine received by the patient. This information should be taken into account by public health policies when deciding on the necessary isolation time for positive subjects.