How do you view the apparent weakening of the virulence of Omicron? How should ordinary people protect themselves? Answers in one article →

On December 5, in an interview with CCTV News, Tong Zhaohui, a respiratory critical disease expert and director of the Beijing Institute of Respiratory Diseases, invited by the State Council's Joint Prevention and Control Mechanism, said that international and domestic monitoring data confirmed that the pathogenicity and virulence of the Omicron variant and its evolutionary branches were significantly weakened compared to the original strain and Delta and other variants .

Director Tong Zhaohui said that the proportion of severe illness and death caused by the Omicron variant is significantly lower than that of the original strain and the variant of concern. This is not only a characteristic of the Omicron variant , but also related to the improvement of the vaccination immunity level of the population and the active prevention strategy adopted by the country . Compared with the global influenza epidemic in 2009, the proportion of pneumonia or severe and critical illness caused by the Omicron variant is relatively low.

So, how do we understand what Director Tong Zhaohui said, "The virulence of the Omicron variant and its evolutionary branches has been significantly weakened", and that compared with the 2009 H1N1 influenza, the proportion of severe cases of the Omicron variant is relatively low? In this case, what should ordinary people pay attention to?

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Like all RNA viruses, the new coronavirus (SARS-CoV-2) is prone to mutating. Since 2019, the World Health Organization (WHO) has named five variants of concern (VOC), of which Omicron is currently the only globally prevalent variant, showing its dramatically increased ability to spread. At the same time, there are increasing reports on the weakened virulence of the Omicron variant. Therefore, how to correctly view and understand this phenomenon is the basis for disease control agencies to formulate corresponding control strategies, and it also helps the public understand and support disease control policies .

01

Novel coronavirus mutation is inevitable

Because RNA viruses lack proofreading activity during replication, the viral genome will produce some mutations with each generation of replication in the cell. Most mutations have little impact on the virus, but some mutations can cause changes in the virus's transmissibility, pathogenicity and immunogenicity .

Compared with the original strain, the genome of the Omicron variant has nearly 100 mutations, including base deletions, insertions, and point mutations [1], and has formed more than 600 evolutionary branches and sub-branches during the spread process. The recent local epidemic in China was caused by the spread of BA.2 and BA.5 branches and their sub-branches. The new coronavirus will continue to mutate. Although some experts believe that the viral genome has entered a stable period, it does not rule out the possibility that new variants of concern will continue to appear in the future. In particular, the phenomenon of genetic recombination between different variants deserves attention. The impact of new variants of concern on the global epidemic cannot be determined at present.

02

The Omicron variant has become more transmissible

Since the discovery of the Omicron variant in November 2021, it has swept the world in just a few months, demonstrating its extraordinary ability to spread.

A team of experts from Nankai University used mathematical models to estimate that the transmission capacity of the Omicron variant is 37.5% higher than that of the Delta variant. In South Africa, the effective reproduction number of the Omicron variant, that is, the number of second-generation cases generated by confirmed Omicron variant infections, is 3.31 times that of the Delta variant, indicating that the Omicron variant has a stronger transmission capacity [2].

Studies have found that the incubation period of infection of the Omicron variant is significantly shortened, the transmission generation is accelerated, the transmission concealment and transmission efficiency are significantly enhanced , and coupled with reinfection caused by immune escape[3], the Omicron variant has a significant transmission advantage compared with other variants.

03

Omicron variants have reduced virulence

In the early stages of the Omicron variant, South African researchers found that its clinical manifestations and consequences were significantly lower than those of the Delta variant.[4] Subsequently, German national surveillance data showed that the hospitalization rate for patients infected with the Delta variant was three times that of the Omicron variant.[5] More and more research and clinical data showed that the virulence of the Omicron variant was significantly weakened, mainly manifested in the significantly lower proportion of severe illness and death than the original strain and other variants of concern.[6] A surveillance data from my country also showed that more than 90% of children infected with the Omicron variant were clinically classified as mild.[7]

In vitro studies and animal experiments have shown that compared with the original strain and other variants of concern, the Omicron variant forms smaller plaques after infecting human cells, has weaker cell fusion ability, and significantly weakened viral replication ability ; in animal models, the Omicron variant also has significantly weakened replication levels in the upper and lower respiratory tracts of infected animals, leading to improved lung pathology and reduced pathogenicity [2,8].

In summary, as the Omicron variant has become the only prevalent variant of concern in China , due to its high transmissibility and weak pathogenicity, China's epidemic prevention and control faces new situations and new tasks. In addition, due to the immune escape characteristics of the Omicron variant, special attention needs to be paid to the protection of pregnant women, children, the elderly and immunocompromised people . Therefore, the continuous monitoring of the genetic mutation of the new coronavirus, especially the Omicron variant, will provide important basic data for epidemic prevention and control, vaccine and drug research and development.

04

Toxicity has weakened, but protection is still important

The virulence of Omicron has been significantly reduced. Does this mean that we no longer need to worry about the new coronavirus? Of course not. Everyone should still pay attention to personal protection and pay attention to the following points:

1. At present, the most important measure of personal protection is to get vaccinated against the new coronavirus .

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2. For the general population, wash hands frequently, wear masks when going out, ventilate frequently, avoid gatherings, maintain a balanced diet, get adequate rest, exercise properly, and maintain a good attitude.

3. Patients with chronic underlying diseases should take medication according to doctor's orders . Patients with chronic respiratory diseases should try to avoid going out when the temperature drops suddenly or in bad weather.

4. If you experience fever, sore throat, cough, or other discomfort , monitor your health . If people at high risk of severe illness have persistent high fever or difficulty breathing, they should go to the hospital in time to avoid worsening of their condition.

References:

[1]Tracking SARS-CoV-2 variants, WHO, https://www.who.int/activities/tracking-SARS-CoV-2-variants

[2]Suzuki R, Yamasoba D, Kimura I, et al. Attenuated fusogenicity and pathogenicity of SARS-CoV-2 Omicron variant. Nature. 2022;603(7902):700-705. doi:10.1038/s41586-022-04462-1

[3]Ma C, Chen

[4]Wolter N, Jassat W, Walaza S, et al. Early assessment of the clinical severity of the SARS-CoV-2 omicron variant in South Africa: a data linkage study. Lancet. 2022;399(10323):437-446. doi:10.1016/S0140-6736(22)00017-4

[5] Sievers C, Zacher B, Ullrich A, et al. SARS-CoV-2 Omicron variants BA.1 and BA.2 both show similarly reduced disease severity of COVID-19 compared to Delta, Germany, 2021 to 2022. Euro Surveill. 2022;27(22):2200396. doi:10.2807/1560-7917.ES.2022.27.22.2200396

[6]Sigal A, Milo R, Jassat W. Estimating disease severity of Omicron and Delta SARS-CoV-2 infections. Nat Rev Immunol. 2022;22(5):267-269. doi:10.1038/s41577-022-00720-5

[7]Li YC, Ma Z, Zhong HY, You HL. Clinical characteristics of children with omicron SARS-CoV-2 infection in Changchun, China from march to April 2022: A retrospective study. Front Pediatr. 2022;10:990944. doi:10.3389/fped.2022.990944

[8]Shuai H, Chan JF, Hu B, et al. Attenuated replication and pathogenicity of SARS-CoV-2 B.1.1.529 Omicron. Nature. 2022;603(7902):693-699. doi:10.1038/s41586-022-04442-5

Author: Public Health Physicians Branch of Chinese Medical Doctor Association

Reviewer: Mao Naiying, Researcher, Institute of Viral Disease Prevention and Control, Chinese Center for Disease Control and Prevention

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