Omicron is posing the greatest challenge yet in China’s ever-changing pandemic situation. With a reproduction number (R0) estimated to be as high as 9.5, one person infected with Omicron can spread the infection to 9.5 persons. Such rapid spread is even faster than chicken pox. And such a fast-spreading virus is difficult to control, forcing the introduction of stricter testing and tracking across China, and even lockdowns in some regions, in order to achieve the goal of “zero-Covid.”
Non-pharmaceutical interventions (NPI) for Covid have been working efficiently, but in the face of a variant with an R0 as high as 9.5, the global situation seems more or less out of control. After it appeared in South Africa, omicron was seen as a severe, difficult to suppress variant. After peaking in South Africa, it subsequently overwhelmed the world. Other countries were not spared in this wave, since their imperfect NPIs could not efficiently and rapidly lower their infection rates.
Some believe that omicron has already evolved into a new virus. But, from a genomic perspective, the virus that battered Shanghai is in fact still the BA2.2 variant. BA3, BA4 and BA5 may emerge in future, but the key is to see whether even more contagious forms will evolve from the existing variants. The variant detected in the Shanghai outbreak with precise sequencing is definitely BA2.2.
Omicron presents an even greater challenge than ever.
1. Omicron’s derivation and evolution
Shanghai, the epicenter of the latest wave of omicron infections, has presented the greatest challenge to China’s efforts to curb Covid-19. Confirmed cases have now exceeded 600,000. Symptoms of the infected have been carefully analyzed to get a grasp of the virus’ major characteristics. We already have cases of large-scale omicron evolution in the international community, with detailed reports on the deviation and evolution of its clinical manifestations.
The ZOE Covid-19 Study published in the Lancet concluded that the delta variant’s more common symptoms, such as headache, fever and systemic inflammatory response syndrome (SIRS) are less severe in the case of omicron. But omicron causes more severe respiratory symptoms, such as a sore throat, hoarseness and unusual muscle pains. In other words, omicron symptoms are clearly lighter, but with a tendency for stronger upper respiratory tract symptoms. This has been true of the experience in Shanghai during this omicron wave.
2. Antibody escape
Most infections have occurred among the vaccinated; in China, with the exception of the elderly, where the vaccination rate is lower, a majority of people have received two doses and even a booster dose. This shows there are two reasons for the reduced omicron symptoms: vaccination and weakened virulence.
Our team at Fudan University published a paper in Cell Host and Microbe recently. Our study showed markedly reduced serum antibody titers against omicron, be it the BA1, BA2 or BA3 variant. So omicron can escape from existing antibodies to some extent. Antibody escape was also discovered in convalescent serum sample tests. That means that omicron’s mutations grant it a certain degree of escape from neutralization, potentially leading to significantly reduced effectiveness of the current antibody therapies and vaccines.
3. Vulnerable groups badly hit by omicron
We recently conducted an in-depth comparison between omicron and influenza — about their inflammatory pathways and intensity of inflammation — and published the results with West Lake University. We found a milder inflammatory response in omicron than influenza, but the response remained severe in vulnerable populations. So while omicron does trigger inflammatory responses, they tend to be weaker than those caused by influenza. And these responses can still be fatal for elderly patients with severe underlying diseases.
4. Vaccines remain effective
Since this outbreak in Shanghai, treating vulnerable populations has been our greatest challenge. The omicron variant can induce severe inflammatory responses among the elderly with underlying diseases such as cardiac-cerebral and renal diseases, diabetes and immune disorder, causing severe or critical Covid-19 illness. Cases resulting in death are clearly related to the induction of inflammatory responses in vulnerable populations and to the aggravation of comorbidities.
In these cases, the effectiveness of vaccines must be relied upon. During the outbreak in Hong Kong some time ago, 90% of the patients had comorbidities, but an analysis of the relationship between vaccination and deaths reveals three-dose protection against death of close to 98%.
Some experts from Shanghai have also published a paper in the Lancet outlining the characteristics of the omicron wave there. It revealed low vaccination and boosting rates, 62% and 38%, respectively, among the over-60s, indicating limited vaccine coverage of the elderly. Meanwhile, among those who died, the vaccination rate was only 4.97%. Based on that data, if we compare the vaccinated and unvaccinated, the death rate among the vaccinated is far lower than that among the unvaccinated of the same age.
Thus, the current priority must be the protection of vulnerable populations. If infection occurs on a larger scale, how many deaths are likely? The answer we get will depend on whether infections have been adequately counted. So we compared case fatality rates (CFRs) for South Korea and Australia, two countries with excellent test coverage and documentation of patient numbers. The result is that we get a CFR of 0.09%–0.1% in the two countries.
This result is close to the CFR for influenza, and has been used to describe the omicron variants in many countries recently. But underlying this statistic is the fact that both countries have very high vaccination rates. Let me give a few examples.
Singapore also has a high vaccination rate — over 80% of people aged 80 and above have been vaccinated — which has contributed to its low CFR at around 0.1%. Even during its spike in cases in the latest wave of the omicron outbreak, it still maintained a low CFR.
In New Zealand, the vaccination rate of people aged 65 and above is 98%. And New Zealand’s CFR is only 0.08%, despite its huge number of infections. So the two countries have something in common.
These CFRs are rough estimates, and include asymptomatic cases. While the best way to estimate CFRs remains subject to debate, rough estimates can be made by dividing the number of deaths by the total number of patients. And CFR can be used as a measure of the severity of a disease. Data from these countries also tells us their vaccination situations, and that too well worth comparing.
Zhang Wenhong is director of National Center of Infectious Diseases and director of Infectious Diseases Department of Huashan Hospital affiliated to Fudan University. The article is based on a speech he delivered at a Chinese Preventive Medicine Association event on May 22.
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