Infection rates of 70% of the population observed within 3 weeks after release of COVID-19 restrictions in Macao, China

We report the rapid spread of SARS-CoV-2 in Macao, Special Administrative Region, China. Recently, the Chinese government announced the “20 measures” and “10 new measures” on November 11 and December 7, 2022 respectively as a relaxation of the Zero-COVID approach. The new measures allow at-home quarantine of asymptomatic and mild cases, reduce the frequency and scale of mass testing, scrap requirements of negative nucleic acid result (NAT) and health code to enter public places, lift mobility restrictions in high-risk areas and promote vaccination rates among the elderly.1COMTEX News Network, Inc China Focus: COVID-19 response further optimized with 10 new measures. 2022, COMTEX News Network, Inc.Google Scholar In line with the new policy, Macao adjusted its COVID-19 control strategy shortly in December 2022. In addition, the Macao government implemented a phased distribution of anti-epidemic kits to all residents to avoid shortage of medication. Some community clinics were designated for consulting COVID-19 patients, to divert cases from hospitals and reduce strains on the healthcare system.2Government Information Bureau of the Macao SAR. Gradual adjustment of the epidemic prevention policy and active preparation of contingency plans for the transition period. 2022 [cited 2023 Janaury 2]; Available from: https://www.gcs.gov.mo/detail/zh-hant/N22LHXdEhA.Google Scholar Located in the Greater Bay Area of China, Macao is one of the most densely populated places with 20,701 people per km.3Statistics and Census Service Government of Macao Special Administrative Region. Population Density. 2021 [cited 2023 January 14th]; Available from: https://www.dsec.gov.mo/en-US/Statistic?id=1.Google Scholar Earlier before the recent new measures, Macao experienced an Omicron outbreak in June 2022 which ended up with 1,821 cases. Multiple stringent measures were implemented including several rounds of citywide and high-risk area mass NATs, mobility restriction, prompt and in-depth epidemiological investigation, centralized medical isolation, free distribution of KN95 masks and COVID-19 rapid antigen test (RAT) kits, Macao successfully contained the local Omicron outbreak of the highly transmissible variant BA.5, to our knowledge the only contained Omicron outbreak outside mainland China.4Lau, D. and L. Chen, Macau has first outbreak in 8 months as mainland china cases ebb. Bloomberg.com, 2022: p. 1-2.Google Scholar Since December 2022, Macao residents with suspected COVID-19 infections gradually adopted the use of RAT for health surveillance and self-medication at home, without reporting to the Health Bureau of Macao, hence the reported case number was unable to reflect the true number of infections. To understand the spread of SARS-CoV-2 in the Macao population, we conducted an online survey during December 27-30, 2022. The survey was distributed online, mainly through social media such as the most popular instant messaging application in China “WeChat” or web link (https://f.wps.cn/w/02djQDa9/), and participation was anonymous and voluntary. General information such as previous or current COVID-19 infection, associated symptoms, and vaccination history were collected. COVID-19 infection was defined as having a positive RAT or NAT result. We collected 5,803 complete questionnaires from 2,285 (39%) males and 3,518 (61%) females, covering about 0.9% of the Macao population. 4,076 (70%) participants were aged between 18-59 years and 178 (3%) were older than 60 years. 3,025 (74%) of the participants received 3 doses of COVID-19 vaccination. 26 (0.05%) and 4,070 (70%) of the participants reported COVID-19 infection before and after December 10, 2022 respectively. The epidemic curves were similar for different age groups (Fig. 1A). The daily COVID-19 infection rate increased gradually for four days after December 10 but quickly reached the peak at 12-14% in about a week (Fig. 1A). The cumulative infection rate rose rapidly to 70% within three weeks (Fig. 1B). 75% (3,014/4,013) of the infections occurred after 3 months of the last COVID-19 vaccination, and those who were vaccinated within 3 months have a lower infection rate than those who were vaccinated for more than 3 months (58%, 854/1,480), indicating short-term protection against infection from COVID-19 vaccination despite immune escape ability of the Omicron variant.5Cui Z., et al., Structural and functional characterizations of infectivity and immune evasion of SARS-CoV-2 Omicron, Cell, 185 (5), 2022, 860-871.e13.Google Scholar Regarding the last COVID-19 vaccination within 3 months, monovalent mRNA vaccine accounts for 37.3%, bivalent mRNA vaccine for 31.3%, and inactivated vaccine for 31.4% respectively. More than 60% of the infected participants presented with fever (≥37.5 °C), dry or sore throat, blocked and runny nose fatigue, headache, or muscle aches, and younger adults (18-59 years) tend to report more symptoms (Table S1). More than half of the infected participants were RAT positive for a duration of 3-7 days. Our survey showed that the Omicron epidemic in Macao has peaked one week before the end of 2022 for all age groups. This study documented the rapid transmission of Omicron in an almost immune-naïve population, with >70% infections in a population of 600 thousand within 3 weeks after a change in the Zero COVID policy. Hong Kong has also adopted a Zero COVID policy but then experienced a major wave of Omicron infection in early 2022, infecting 45% of the population while imposing more stringent control measures than Macao,6Lau J.J. et al.Population-based sero-epidemiological estimates of real-world vaccine effectiveness against Omicron infection in an infection-naive population, Hong Kong, January to July 2022. Cold Spring Harbor Laboratory, 2022Crossref Scopus (0) Google Scholar while the Omicron epidemic started in November 2022 in Beijing and have reached >70% infection around one week earlier than Macao.7Leung, K., et al., Estimating the transmission dynamics of SARS-CoV-2 Omicron BF.7 in Beijing after the adjustment of zero-COVID policy in November - December 2022. Nat Med, 2023 Jan 13. Epub ahead of print.Google Scholar Our survey may have underestimated the infection rate in Macao, as asymptomatic cases may not have tested with RAT or NAT, and there may be some missed infections for participants who responded earlier. However, it compensates the lack of surveillance in Macao and could monitor the future rebound due to emerging variants such as XBB. As China has now transitioned from managing COVID-19 infections to managing severe cases, early preparedness such as administrating booster vaccine to the elderly and high-risk population, and stockpiling of antivirals should reduce morbidity and mortality in the future epidemic waves. This study was approved by the ethics committee of Medical Ethics Committee of Macau University of Science and Technology (Approval No: MUST-FDCT-20230113001) Not applicable The data that support these findings are available on reasonable request from the corresponding author. Data are not publicly available due to concerns regarding research participant privacy. None reported. This work was supported by National Key Research and Development Program of China (No. 2022YFC2600705); Self-supporting Program of Guangzhou Laboratory, Grant No. SRPG22-007; Science and Technology Development Fund of Macau SAR(005/2022/ALC); Science and Technology Program of Guangzhou (No. 2022B01W0003); Science and Technology Program of Guangzhou (Grant No. 202102100003); Science and Technology Development Fund of Macau SAR(0045/2021/A); Macau University of Science and Technology (FRG-20-021-MISE).