在刚过去的圣诞长假期及除夕，新冠病毒变异病毒株Omicron在香港社区引起一系列的传播链。目前已有数据显示，Omicron的传播能力较原毒株或其他变异株高，而疫苗对Omicron的中和能力亦较对原毒株低。Omicron疫情一触即发，情况令人忧虑。有见及此，香港中文大学（中大）医学院赛马会公共卫生及基层医疗学院、香港城巿大学（城大）赛马会动物医学及生命科学院领导的研究团队，利用数学模型评估本港在大部分巿民已接种疫苗的情况下，Omicron带来的潜在风险。
假设 (i) 已有约65%人口接种至少一剂疫苗、(ii) 接种两剂疫苗的有效保护感染比率为50%（科兴）及70%（復必泰）、(iii) Omicron基本传染数 (R0) 为 8（当人口没有抗体、没有使用疫苗或没有实施社交距离措施的情况下）、(iv) 抗体随时间下降、(v) 追踪检测效能与第四波疫情一样，及 (vi) Omicron重症率为Delta的一半，研究组就以下两个情况为香港疫情作估算：
若社交接触程度一直维持在过去两星期（包括圣诞及元旦假期）的水平，由Omicron引起的第五波疫情将有超过300万人受感染，及超过17万人得重症；
由一月七日起生效的收紧社交距离措施，以致社交接触程度较过去两星期的水平
2.1. 减少25%（即每天平均接触的人数降至14），第五波疫情会有大约25万人受感染，及大约1.5万人得重症；
2.2. 减少40%（即每天平均接触的人数降至11），第五波疫情会有大约1.25万人受感染，及大约700人得重症；
2.3. 减少到疫情以来的最低点（即2020年7至8月的第三波期间），即减少55%（即每天平均接触的人数降至8），第五波疫情会有大约1,100人受感染，其中大约50人得重症。
**************************************************************************
During the past Christmas and New Year holidays, Omicron, the variant of SARS-CoV-2, has been establishing a series of transmission chains in the Hong Kong community. Current data reveals that Omicron has a higher transmissibility than the original strain or other variants, and the neutralising ability of the vaccine against Omicron is also lower than that against the original strain. The Omicron epidemic is looming, and the situation is worrying. In the light of this, the research team led by JC School of Public Health and Primary Care, at The Chinese University of Hong Kong’s (CUHK) Faculty of Medicine (CU Medicine), and the Jockey Club College of Veterinary Medicine and Life Sciences, City University of Hong Kong are using a mathematical modelling approach to assess the possible risks of Omicron outbreaks in a majority vaccinated population in Hong Kong.
This study employs an age stratified mathematical model using social mobility levels as proxy estimate of social contact, taking into account: (i) the age-specific susceptibility to COVID-19 infection, (ii) the effectiveness of the two COVID-19 vaccines in Hong Kong, (iii) the mobility data during the pandemic period, (iv) the social contact data in the community during the pre-COVID period, to simulate the number of infections that may be caused by the potential fifth epidemic wave under different interventions.
Assuming (i) 65% of the population being vaccinated with at least one dose of the vaccine, (ii) the vaccine effectiveness against infection as 50% (Sinovac) and 70% (BioNTech), (iii) the basic reproduction number (R0) of Omicron as 8 (when the entire population is susceptible, not vaccinated, or there is no exercising of social distancing measures) and (iv) antibody waning across time, (v) contact tracing efficacy similar to that in the fourth wave, and (vi) the severity rate of Omicron being half of that of Delta, the research team forecasts the upcoming epidemic based on these two scenarios:
If the social contact level remained at the same level as during the Christmas and New Year holidays in the past two weeks, the fifth epidemic wave triggered by Omicron would lead to more than 3 million infections, and more than 170 thousand severe cases.
If the tightened social distancing measures effective from 7 January would:
2.1. decrease the social mobility by 25% (daily number of social encounters =14), then the fifth epidemic wave would cause about 250 thousand infections and about 15 thousand severe cases;
2.2. decrease the social mobility by 40% (daily number of social encounters = 11), then the fifth epidemic wave would cause about 12.5 thousand infected cases and about 700 severe cases;
2.3. decrease the social mobility down to the trough in the pandemic (between July-August 2020, during the third epidemic, i.e., the social mobility decreases by 55% which corresponds to daily number of social encounters = 8) then the fifth epidemic wave would cause about 1,100 infections and about 50 severe cases.
Press release: Assessment of Omicron outbreak in Hong Kong after reimplementation of some of the toughest social distancing measures effective from 7 January
相关报道：
文汇报 - 市民日接触若降至8人 全港染疫料仅千人
信报财经新闻 - 中大城大研究估算第五波25万人中招
香港经济日报 - 急堵社区隐形传播 谷针配套从速改善
星岛日报 - 研究：港防疫不加辣 或致逾300万人染疫
香港商报 - 专家推算过去两周社交达疫前水平 若不限聚恐逾300万人染疫
澳门日报 - 市民圣诞元旦日均接触三十四人 研究：不收紧料三百万人感染
文汇报 - 中大城大研究：不减社交接触 恐三百万人染疫
东方日报 - 疯传将停课 教育局否认
联合早报 - 港中大城大研究：若不减社交接触 恐有300万人染疫
Channel 8 - 研究：香港第五波疫情或感染300万人
HK01 - 中大城大研究：社交接触程度若无减 第五波疫情致逾300万人中招
RTHK - 研究指若不收紧社交距离 第五波疫情或3百万人感染
商业电台 - 中大城大研究：倘无收紧措施 第五波有逾300万人受感染
TVB News - 中大城大推算本港新一波疫情或致约25万人感染
香港中通社 - 研究：港人社交接触若维持 恐有逾300万人受感染
东网 - 研究指圣诞元旦市民日接触34人 情况持续或致逾300万人染新冠
头条日报 - 中大城大研究：无减社交接触 本港逾300万人受感染 逾17万人得重症
中时新闻网 - 港疫情一触即发 中大研究：若无收紧措施 将逾300万人受感染
The Standard - SOGO saleswoman in Omicron net
SCMP - Omicron: infections could hit 250,000 within 6 months if local cases rise and Hong Kong does not tighten social-distancing measures, study warns