FRIDAY, April 8, 2022 (HealthDay News) -- If you're vaccinated and get COVID-19 anyway, which variant you have and whether you've been boosted make a difference.
Symptoms last longer when breakthrough infections are caused by the Delta variant and not the more contagious Omicron variant, according to European researchers who are reporting other differences in how SARS-CoV-2 variants affect vaccinated patients.
They studied nearly 10,000 people, ages 16 to 99, in the United Kingdom who tested positive for the virus after receiving at least two doses of any COVID vaccine. Half got sick when Delta was the dominant strain and half when Omicron was dominant.
On average, researchers found, vaccinated patients with Delta had symptoms for nine days; those with Omicron, for seven.
Booster shots shortened the number of days spent suffering even more, the study showed.
For patients who had two doses, symptoms averaged 9.6 days for Delta and 8.3 for Omicron. Two shots plus a booster cut that to 7.7 days for Delta and 4.4 for Omicron.
“The shorter presentation of symptoms suggests -- pending confirmation from viral load studies -- that the period of infectiousness might be shorter, which would in turn impact workplace health policies and public health guidance," said study authors Cristina Menni and Tim Spector of King’s College London.
The study is scheduled for publication in The Lancet and presentation at a meeting of the European Congress of Clinical Microbiology and Infectious Diseases in Lisbon, Portugal, April 23-26. The authors made the comments in a meeting news release.
The researchers also found that loss of smell was much less common in those with Omicron (17%) than with Delta (53%), but the risk of sore throat was 55% higher and hoarseness 24% higher among those with Omicron.
Patients with Omicron also were about half as likely to have at least one of three classic COVID symptoms -- fever, loss of smell and persistent cough -- than those with Delta, the study found.
In addition, Omicron patients were 25% less likely to admitted to the hospital than Delta patients (1.9% vs. 2.6%), and Omicron patients were 2.5 times more likely to recover within a week than those with Delta, the findings showed.
"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," said Linda Houhamdi and Pierre-Edouard Fournier of Aix-Marseille University and Public Assistance Hospital of Marseille in France. They made these comments in an editorial that will accompany the findings.
The findings dovetail with emergence of a new Omicron variant in the U.K.
For more on COVID variants, see the U.S. Centers for Disease Control and Prevention.
SOURCE: European Congress of Clinical Microbiology and Infectious Diseases, news release, April 7, 2022