University of Hong Kong study: death risk of under-vaccinated cases in Hong Kong’s Omicron epidemic is similar to earlier

What is the fatality rate caused by the dominant strain Omicron BA.2 currently circulating in the world? In fact, there is no unified understanding. In a recent study by the University of Hong Kong, researchers analyzed the fifth wave of the epidemic in Hong Kong and concluded that those who have not completed the full course of the new crown vaccination, facing the Omicron BA. The risk of death is similar to the original strain.

The study was recently published on the preprint website medRxiv, titled “Infection of SARS-CoV-2 Omicron mutants in Hong Kong from January to March 2022 “Epidemiology of infections with SARS-CoV-2 Omicron BA.2 variant in Hong Kong, January-March 2022). The research team is from the School of Public Health of the University of Hong Kong, the WHO Collaborating Centre for Epidemiology and Control of Infectious Diseases, and the Hong Kong Health Data Discovery Laboratory. The research team wrote that during the COVID-19 pandemic In the first two years of the epidemic, Hong Kong experienced four relatively small waves of outbreaks, reporting a total of 12,631 (1.6 per 1,000 people) confirmed cases of COVID-19 and 213 deaths. But in early 2022, it experienced a wave of epidemics dominated by Omicron (BA.2.2), which can be described as a real “pandemic” for Hong Kong.

Starting at the end of 2021, Omicron BA.2 eventually dominated the fifth very large wave of the epidemic in Hong Kong, and finally reached its peak in early March 2022. According to the latest data disclosed by the Hong Kong Department of Health, as of 00:00 on April 17, the fifth wave of the epidemic in Hong Kong had resulted in a total of 8,926 deaths who had tested positive for the new coronavirus.

This latest study analyzes the epidemiological characteristics of the fifth wave of SARS-CoV-2 infections in Hong Kong. Since early 2020, Hong Kong has responded to the COVID-19 outbreak with intensive public health and social measures, including testing and tracing, isolation of confirmed cases, isolation of close contacts and arrivals, and strict travel and border restrictions, the study writes. , community-wide social distancing measures, etc. “These measures have been very effective in controlling the previous four local outbreaks, but have not prevented the fifth wave of the pandemic.”

In the fifth waveThe number of infections in Hong Kong has reached an all-time high, with more than 1.1 million officially reported confirmed cases. The daily number of cases detected by RT-PCR nucleic acid testing and rapid antigen testing peaked on March 4. It has experienced exponential growth for more than a month, with a doubling time of 3.4 days. The number of confirmed local COVID-19 cases and deaths in Hong Kong in the first four (group A) and fifth (groups B and C) waves.

In the first four waves (group A) and the fifth wave (groups B and C) , the number of confirmed local cases and deaths of COVID-19 in Hong Kong.

Hong Kong is one of the first places in the world to detect the Omicron variant, and it is also the first area in China to attack Omicron. As mentioned in the paper, as of January 22, a total of 136 confirmed cases of local infection with Omicron were found in Hong Kong, of which 72% (98/136) had identifiable transmission chains. These cases are associated with 4 clusters (initiated by imported cases), with the largest cluster comprising 49 cases.

Of the 98 cases with an identifiable chain of transmission described above, 34% (33) were Omicron BA.2, 55% (54) were female, 73 % are those who have completed the primary series of vaccinations. In all 98 cases, virus exposure information could be established (26% of the virus was a single exposure time), and 80 of them (82%) reported symptoms at the time of case diagnosis. The mean age of BA.1 cases was 44 years, and the mean age of BA.2 cases was 30 years.

In this study, a total of 80 patients (57 BA.1 and 23 BA.2) were included in the incubation period analysis. The mean incubation periods of Omicron BA.1 and Omicron BA.2 were 4.58 (±1.72) days and 4.42 (±1.42) days, respectively. It is estimated that 95% of patients infected with Omicron BA.1 and Omicron BA.2 develop symptoms within 7.7 and 7.0 days of exposure.

Next, the research team also conducted a serial interval analysis, that is, the time interval from the onset of the first-generation case to the onset of the second-generation case. For BA.1, the estimated mean and median series intervals were 3.30 (±1.95) days and 3.17 days, respectively; for BA.2, the estimated mean and median series intervals were 2.72 (±1.51) days and 2.52, respectively sky.

They concluded that these data suggest that Omicron has a shorter incubation period, serial interval, etc. compared to other SARS-CoV-2 variants.

The research team also focused on the risk analysis of the fifth wave of the epidemic (CFR, the number of deaths of patients divided by the number of all patients with the disease). The paper wrote that as of March 23, the fifth wave of the epidemic There were 6,320 deaths in China. Of these, 103 were reported before February 15, in the early stages of the fifth wave, when all COVID-19 cases were confirmed only by RT-PCR, as in the previous four waves.
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Of note, they estimated that the age-specific case-fatality risk (CFR) of cases in the fifth wave who did not complete the primary series of vaccinations was the same as the first among all age groups. Cases in the fourth wave had a similar risk of death.

The paper noted that in the first to fourth waves, patients aged 80 and older had the highest mortality rate ( 24.9%, 95% CI: 20.9, 29.3), similar to unvaccinated patients in the same age group in the fifth wave (21.7%, 95% CI: 17.1, 26.8). In the fifth wave, the primary series was not completed The case fatality rate (CFR) appeared to be twice as high in the vaccinated 80-year-old cohort as in the same age group who completed the primary series (11.1%, 95% CI: 4.2, 22.6), with similar cases in the 64-79-year-old cohort .

The research team concluded that the high death toll in the fifth wave of Hong Kong was mainly due to the high incidence of infection in a short period of time and the higher vaccination rate of the elderly group. Low. At the beginning of the fifth wave of the epidemic, the overall vaccination rate in Hong Kong was about 70%, but only 50% and 20% of people over 65 and 80 years of age, respectively, completed the primary series of vaccinations. Correspondingly, of all age-related deaths as of March 23, 92.5% (5,844/6,318) were those over 65, and 70.8% (4,472/6,318) were those over 80. Age-stratified estimates of mortality risk of COVID-19 cases in waves 1-4 and 5 in Hong Kong by vaccination status.

Age-stratified estimates of mortality risk of COVID-19 cases in waves 1-4 and 5 in Hong Kong by vaccination status.

According to the vaccination situation, the first – 4th wave and 5th wave COAge-stratified estimates of mortality risk in VID-19 cases.

The study also highlights that in animal models, Omicron infection shows reduced pathogenesis and appears to be relatively less severe in South Africa and elsewhere. However, their analysis of the study, based on data from Hong Kong, found that the risk of death in unvaccinated cases in this fifth wave was similar to that in previous waves, suggesting that BA.2 may not be more endogenous in severity than How low is the ancestral strain.

The research team believes that the study underscores the importance of achieving high vaccination coverage, especially among older adults. They believe that 3 doses of Sinovac inactivated vaccine or 2 doses of mRNA vaccine BNT162b2 is very effective in protecting the elderly over 60 against severe disease.

The preliminary data analysis of the death case report of the new crown previously disclosed by the Hong Kong Department of Health also showed that in the fifth wave of the epidemic, the median age of the death cases was 86 years old. 73% of the deaths were unvaccinated, more than 95% of the deaths were elderly people over 60 years old, and 92% of the deaths had known long-term conditions.

Data analysis also showed that the overall case fatality rate of the fifth wave of the epidemic in Hong Kong was 0.74%. Among them, the case fatality rate of unvaccinated patients was 2.97%; the case fatality rate of patients who received 1 dose of vaccine was 0.97%; the case fatality rate of patients who received 2 doses of vaccine was 0.16%, and the case fatality rate of patients who received 3 doses of vaccine was 0.04%. The report highlights that with any three doses of the vaccine, the risk of death is substantially reduced, especially in older age groups.

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