End of zero Covid in China: consequences and risks for a population with low immunity

China is the only major country that, until recently, continued to implement a “zero Covid” strategy. Since December 7, she is now backtracking. Other countries, including Australia, New Zealand and Singapore, had also sought to completely eliminate Covid from their territory at the start of the pandemic, but all had finally abandoned this approach. The growing social and economic costs had become unsustainable, as had the efforts required… in the face of the realization that the local elimination of Covid could only be transitory.

In the People's Republic of China, the health strategy which relied on measures like mass PCR testing, shutting down entire cities and provinces, or quarantining anyone who may have been exposed to the virus, has in turn become unsustainable.

La hardness and often arbitrary application zero Covid has fueled growing fatigue and resentment among the population, which has recently resulted in large public demonstrations.

Restrictions have also shown their limits in the face of Omicron : less severe but more transmissible, this variant has a incubation period shorter than previous SARS-CoV-2 lineages, and it circumvents largely the protection against infection conferred by the original vaccines.

It is understandable that the Chinese authorities are now finally taking steps to relax restrictions… However, exiting from a zero Covid policy has been painful for all the countries that have done so. And China will be no exception, it even faces unique challenges in this transition.

Low immunity of the Chinese population

China's strict control over its population has enabled it to prevent a general transmission of Covid to all of its (huge) territory since the beginning of 2020 – which is a feat. The nearly 10 million cases reported to theWorld Health Organization the last three years (the figures differ according to the sources) represent only a tiny part of its 1,412 billion inhabitants. But this achievement has the unfortunate consequence that its population has only acquired minimal immunity to Covid through exposure to the virus.

What about vaccine immunity? The vaccination rate in china are comparable to those of Western countries… But they show an unusual feature: they decrease with age. While they are the most exposed to the risk of serious forms of Covid, the elderly are thus the least vaccinated demographic group with only 40% of people over 80 received three doses.

Another point: the effectiveness of vaccines against transmission has been severely tested, especially since Omicron began to spread at the end of 2021. However, the protection against the most severe forms and death provided by the mRNA vaccines used by Western countries remained solid.

But China has used vaccines different from its design, called "inactivated", manufactured by the companies Sinovac and Sinopharm. This type of vaccine is based on pathogens (in this case SARS-CoV-2, the virus responsible for Covid-19) which are killed, or inactivated, before their inoculation. While these vaccines are generally safe, they tend to cause weaker immune responses that new technologies – such as those used in mRNA vaccines (Pfizer and Moderna) or adenoviral vector (AstraZeneca and Johnson & Johnson).

The performance of Chinese vaccines has thus been mixed. While two doses of the Sinovac vaccine seem to have made it possible to reduce deaths by 86% in Chile, the results in Singapore suggest a less protection against severe forms than their mRNA counterparts.

Admittedly, the Omicron variant (via its numerous sub-variants), dominating worldwide, is associated with a significantly lower disease severity and mortality rate than the Delta variant that it replaced… But it remains a major threat for populations with low immunity, in particular the elderly.

The case of Hong Kong: a precursor?

At the start of 2022, Hong Kong faced similar problems to mainland China, with low prior exposure of its population to the virus. Hong Kong even had even lower vaccination rates for the elderly than China currently has, but a stronger healthcare system.

Yet the Omicron wave that swept through the megalopolis in March 2022 resulted in more cumulative deaths per million population in days than many countries have experienced throughout the pandemic…

Our World in Data/Johns Hopkins University, CC BY

Covid infections are now rising rapidly in China, exceeding 30 new cases daily early December (to fall to less than 9000 these days, due to the end of systematic PCR tests: beware, these figures are no longer significant, individuals no longer necessarily informing the authorities of the results of self-tests carried out at home, editor's note). With the easing of restrictions and the shutdown of the main travel tracking application, there is no doubt that the increase in infections will continue.

Given the low level of immunity in China, a sharp increase in the number of cases could likely lead to a large number of hospitalizations and lead to a dramatic number of deaths.

If we assume that 70% of the Chinese population is infected in the next few months, and that 0,1% of those infected die (a conservative estimate of the mortality rate of omicron in a population with low exposure to SARS-CoV- 2), a simple calculation suggests that the number of deaths could be close to one million. Modeling by Fundan University (Shanghai) arrived at a figure of 1,55 million.

At this point, there is little China can do to prevent a significant number of cases and deaths. All vaccination campaign focusing on the most vulnerable, however, is still likely to be beneficial.

Chinese health services are quite fragile and the shortage of intensive care beds represents a particular vulnerability. A gradual lifting of restrictions as other countries have done is one option to try to "flatten the curve" and prevent its health system from being overwhelmed. Effective referral of patients, including ensuring that only those most in need of care are admitted to hospital, could help reduce the number of deaths if the epidemic explodes.

A vulnerable population

A major wave of Covid in China will not necessarily have a significant impact on the global situation. The SARS-CoV-2 lineages that are currently spreading in the country, as BF.7 (which is transmitted faster and with a shorter incubation period and greater ability to infect than other Omicron variants; with a number of people infected in the absence of transmission control measures by an individual infected, or R0, of 10 or more), are already found elsewhere in the world.

Moreover, circulation in a population with little immunological protection should not exert significant additional pressure on the virus to the point that it must develop new variants to continue to spread.

But for China itself, the situation is different. It could face a possible humanitarian disaster, and that is a much bigger challenge.

The Chinese authorities were the first to take unprecedented measures to halt the spread of the virus and to champion it, providing the planet with a drastic model for managing the pandemic. China then applied these measures more ruthlessly and for longer than any other major country.

Particularly effective at first, the zero Covid policy turns out to be, in the long term, almost "futile" in the face of the adaptability of SARS-CoV-2. While its population has been spared more than many others and is therefore less immunologically protected, China is now overtaken by the social and economic costs of this strategy. And the virus will continue to spread, as it has everywhere else.

Francois Balloux, Chair Professor, Computational Biology, UCL

This article is republished from The Conversation under Creative Commons license. Read theoriginal article.

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