December 1, 2023

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Over a million people study reveals 59% lower risk of hospitalization with Omicron

Over a million people study reveals 59% lower risk of hospitalization with Omicron


The Lancet: Over a million people study reveals 59% lower risk of hospitalization with Omicron, except for this age group…

Since Omicron (B.1.1.529) was discovered in South Africa in late November 2021 , this new coronavirus variant has swept more than 133 countries around the world in just 5 months, becoming the main strain currently circulating.


Although some previous studies have shown that Omicron causes milder disease symptoms compared to Delta, more detailed data are needed to understand the public health impact of Omicron transmission.


Recently, a large-scale national study published in the Lancet by Professor Tommy Nyberg’s team at the University of Cambridge in the UK collected data on more than 1 million patients with COVID-19 infections in the UK between November 2021 and January 2022. “The Delta strain of the new coronavirus was used as a control to analyze and compare the severity of Omicron and Delta’s infection in people of different ages and immune status, including changes in the risk of medical treatment, hospitalization and death.


Over a million people study reveals 59% lower risk of hospitalization with Omicron

Among the 1,516,702 COVID-19 cases, there are 1,067,859 Omicron infections and 448,843 Delta infections, of which 5,983 (1.3%) Delta and 102,957 (9.6%) Omicron infections are re-infections, that is, even if the previous If you have been infected with the new coronavirus, you are also at risk of re-infection. (Reinfection is defined as: having been infected with the new coronavirus 90 days or more ago)


In terms of infection severity, Omicron-infected individuals had a 44% lower risk of hospital visits overall compared with Delta (HR 0 56, 95% CI 0 54–0 58) and a 59% lower risk of hospitalization within 14 days of infection ( 0.41, 0.39–0.43) , and a 69% lower risk of death within 28 days of infection (0.31, 0.26–0.37) .


However, if we subdivide the infected people of each age group, we will find that the risk reduction of hospital visits, hospitalization and death of Omicron infected people aged 20-69 is increasing, and it increases slightly after the age of 70. It is still more than 50% lower than that.


There is only one age group exception, and that is children aged 0-9, for whom the risk of hospital visits and hospitalization due to Omicron infection (adjusted HR 1 10, 95% CI 0 85–1 42) was not lower than Delta.


Although no data on the risk of death among children infected with the disease were given in the study, some studies have shown that the mortality rate of children aged 0-4 regardless of the Omicron or Delta stage is very low, only 0.5% of children during hospitalization are Died from COVID-19 infection (from Morbidity and Mortality Weekly Report, March 15, CDC) .


Over a million people study reveals 59% lower risk of hospitalization with Omicron


In terms of vaccine protection, the protective effect of the vaccine against Omicron was lower than that of Delta, especially for those who received only one or two doses, however, compared with the unvaccinated, the third booster dose was still able to provide Omicron breakthrough infection provides 70% protection (mRNA vaccine) .


The protective effect of the vaccine on Omicron is weakened, while the risk of hospital visit, hospitalization and death risk of Omicron-infected patients has decreased compared with Delta.


In addition, in addition to vaccinations that can produce new coronavirus antibodies in the body, people who have been infected with the new coronavirus also have certain antibodies that produce protection. The study found that people who were previously infected with the COVID-19, after re-infection with Omicron, had a 45% lower risk of hospitalization (0 55, 95% CI 0 48–0 63) and an 82% lower risk of death (0 18, 0 ). 06–0.57) , which is equivalent to the effect of two doses of AstraZeneca’s adenovirus vector vaccine or one dose of Pfizer/Moderna mRNA vaccine.


Over a million people study reveals 59% lower risk of hospitalization with Omicron

The protective effect of vaccination against the Delta strain (red) and against the Omicron strain (blue) compared with the unvaccinated. Left: AstraZeneca adenovirus vector vaccine Right: Pfizer/Moderna mRNA vaccine

This study is currently the largest comparative study of Omicron and Delta, which confirms that the toxicity of Omicron is significantly reduced compared with Delta, but this decline is not significant in children aged 0-9. On the one hand, it may be due to the high transmission of Omicron On the other hand, compared with previous strains, Omicron mainly infects the upper respiratory tract, and children have smaller airways, more pronounced symptoms, and higher rates of doctor visits and hospitalizations.


To protect children from infection, in addition to vaccinating school-aged children, family members and people around them should also “receive everything”. Some data show that compared with one parent’s vaccination or even zero vaccination, in families where both parents are vaccinated , young children are much less likely to contract the COVID-19. Pregnant women vaccinated against Covid-19 can also protect their newborns from infection.


The study also noted that although the vaccine’s protection against Omicron declined, the booster dose still significantly reduced the risk of hospitalization and death.


Finally, although Omicron is less virulent than Delta, as long as the virus is still spreading and evolving, it is possible to have a highly transmitted and highly virulent strain, like the BA.2 subclade of the Omicron variant that is sweeping everywhere today , WHO calculated based on the Danish epidemic data, this sub-variant is 30% more contagious than BA.1, and both transmissibility and concealment are stronger.


WHO spokesman Tedros Adhanom Gebreyesus told reporters in Geneva on March 18 that it was precisely because of the rampant BA.2 that after weeks of declines in confirmed cases, the number of COVID-19 cases reported globally was increasing again, particularly in parts of Asia.





[1] Nyberg T, Ferguson NM, Nash SG, et al. Comparative analysis of the risks of hospitalisation and death associated with SARS-CoV-2 omicron (B.1.1.529) and delta (B.1.617.2) variants in England: a cohort study [published online ahead of print, 2022 Mar 16]. Lancet. 2022;S0140-6736(22)00462-7. doi:10.1016/S0140-6736(22)00462-7
[2] Post LA, Lorenzo-Redondo R. Omicron: fewer adverse outcomes come with new dangers [published online ahead of print, 2022 Mar 16]. Lancet. 2022;S0140-6736(22)00514-1. doi:10.1016/ S0140-6736(22)00514-
[4]Marks KJ, Whitaker M, Agathis NT, et al. Hospitalization of Infants and Children Aged 0-4 Years with Laboratory-Confirmed COVID-19 – COVID-NET, 14 States, March 2020-February 2022. MMWR Morb Mortal Wkly Rep. 2022;71(11):429-436. Published 2022 Mar 18. doi:10.15585/mmwr.mm7111e2

Over a million people study reveals 59% lower risk of hospitalization with Omicron

(source:internet, reference only)

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