Omicron subvariant BA.5 is highly contagious but containable: Successful experience from Macau

Abstract

IntroductionDue to its high transmissibility and immune escape, Omicron subvariant BA.5 has become the dominant strain of the SARS-CoV-2 virus and led to escalating COVID-19 cases, how to cope with it becomes an urgent issue. A BA.5 infection surge burst out on 18 June 2022 and brought an unprecedented challenge to Macau, the most densely populated region worldwide. This study aimed to analyze the characteristics of this outbreak and summarize the useful anti-epidemic measures and experiences during this outbreak.MethodsAll data were obtained from the Government Portal of Macao SAR (https://www.gov.mo), and the Special Webpage Against Epidemics, the Macao Health Bureau (www.ssm.gov.mo). An epidemiologic study was performed to analyze epidemic outcomes, including the infection rate, the proportion of symptomatic cases, the case fatality ratio (CFR), etc. Data were analyzed using SPSS Version 20. A p-value <0.05 was considered statistically significant. The anti-epidemic measures and experience were reviewed and summarized.ResultsThe BA.5 outbreak resulted in 1,821 new cases, which was significantly more than the cumulative cases of the previous variants of COVID-19 in Macau. The symptomatic cases accounted for 38.71% of the total cases, which was higher than that of the previous variants. After 6-week concerted efforts, Macau effectively controlled the outbreak, with an infection rate of 0.27%, which was much lower than many BA.5-attacked regions. The CFR was approximately 0.86%, which was not statistically different from that of previous variants. Six victims were chronically ill senior elders and their vaccination rate was much lower than the average level. Macau took a comprehensive anti-epidemic strategy to win a quick victory against BA.5, especially the “relatively static” strategy that was first formulated and applied by Macau for the management of the COVID-19 pandemic. Successful experience showed that although BA.5 was highly contagious, it could be contained by comprehensive anti-epidemic measures, including adequate anti-epidemic preparation, herd immunity through vaccination, repeated mass nucleic acid tests and rapid antigen tests, KN-95 mask mandate, the “relatively static” strategy, precise prevention and control, epidemiological investigation and tracing, and traditional Chinese medicine treatment, etc.DiscussionIn Macau, compared with the previous subvariants, BA.5 is associated with increased transmissibility and a higher proportion of symptomatic cases, however, the risk of death remains similar, and the infection rate is much lower than that in many other BA.5-attacked regions. BA.5 is highly contagious but still containable, Macau's experience may offer hints for the regions experiencing the BA.5 waves to choose or adjust a more rational anti-epidemic strategy.

Epidemiology and analysis of SARS-CoV-2 Omicron subvariants BA.1 and 2 in Taiwan

“…In addition, we observed that the CFR for BA.5.x subvariants, which accounted for 100% of isolates in October 2022, was 0.16% in Taiwan. Recent studies have suggested that the CFR for BA.5 subvariants was 0.86% in Macau 18 and 0.41% in the United States of America 19 . Further results by Takahashi et al 20 suggested that age‑specific CFRs for cases with BA.5 sublineages at 10‑year intervals from 50, 60, 70 and ≥ 80 years were 0.03%, 0.05%, 0.39%, and 1.81%, respectively.…”

Change in the Clinical Picture of Hospitalized Patients with COVID-19 between the Early and Late Period of Dominance of the Omicron SARS-CoV-2 Variant

“…However, in parallel with these phenomena, a milder clinical course of COVID-19 and lower mortality caused by the Omicron variant has been documented compared to previous pandemic waves [4,13,14,25,26]. Available analyses evaluating the clinical picture and outcomes of COVID-19 focus on the comparison between infections caused by the Omicron variant with other VoCs or separately describe different periods of Omicron dominance [27][28][29][30]. There is a lack of publications comparing the severity of the clinical course of SARS-CoV-2 infection in patients hospitalized in the early and late periods of Omicron prevalence.…”

“…In addition to the potential for immune escape due to numerous mutations, the importance of the therapeutic escape of Omicron subvariants is also emphasized [8,12,29,46]. This resistance or reduced susceptibility compared to previous VoCs applies to monoclonal antibodies, while the antiviral drugs used so far remain active against recombinant subvariants of Omicron [5,8,47,48].…”