The Characteristic of infection in BA.2, BA.5 to BF7：A retrospective study

Abstract

Background Omicron has become the dominant SARS-CoV-2 variant worldwide. While comparisons of infection characteristics in various evolutionary variants remain scarce, it is essential to analyse the evolution and make important additions to the disease spectrum. Methods We used a retrospective case study to collect 802 cases of primary infection with BA.2, BA.5, and BF.7 sub-variants in three SAR-COV 2 outbreaks in China and identified infection characteristics using demographic, laboratory examinations, and clinical data. All data were analyzed using the Chi-square test and One-way ANOVA, with p < 0.05 as a statistically significant criterion. Results The results showed that the proportion of symptomatic cases of infection by BA.2, BA.5, BF.7 were 80.9%, 70.5%, and 61.4%. Moreover, the initial asymptomatic cases without clinical progression among the three variants were 41.8%, 35.9%, and 57.5%, respectively. Our statistical results suggest that mutations confer more asymptomatic infections and shorter incubation periods, sequence intervals, and HT. In the population receiving the booster vaccine, a longer duration of vaccination to positive indicates lighter symptoms. The emergence of sub-mutant strains has led to a decrease in the proportion of symptoms in the elderly and the clinical severity and viral load of those infected at lower ages. Gender differences caused by mutations were more commonly manifested in neurological symptoms such as myalgia. The CT value of the initial positive test reflected the severity of the disease in the BF.7 infected individuals in contrast to the early variants. All manifestations of infection with BF.7 became milder compared to the previous sub-variants. Conclusion The effect of the variation was gradually weakening but showed differences in ages and genders. Although the mutation causes immune evasion, the vaccine significantly reduces symptoms and disease duration as the mutation appears. More attention should be paid to the evolution of mutant strains to prevent a larger epidemic.