Covid in China: why such an explosion of cases? What are the consequences for Europe?

China is currently overwhelmed by a large wave of Covid infections and deaths. However, we do not know exactly the seriousness of the situation, because of the large gaps in the official reports… Everything nevertheless leads us to believe that the situation is very difficult. According to several media, the hospitals and morgues are overflowing and some provinces, such as Henan, would see their population infected at 90%.

Beyond the end of its zero Covid policy in early December, how did China get there? And how can the situation evolve?

Despite the popular perception that the current wave of infections is a direct result of the lifting of restrictions a month ago, that is not entirely true. The cases were already increasing at the moment.

As an epidemiologist, I believe that this explosion is largely due to the fact that China has pursued its zero Covid strategy for too long after vaccinating its population.

Poor coordination in relation to its vaccination campaign

We know that the immunity conferred by vaccines decreases in the following months injection. A paper currently in preprint (thus a study that has yet to be reviewed by other scientists) has shown that, eight months after the booster, much of the protection against infection is lost. Protection against severe forms of the disease is more durable, but it also decreases.

However, China's vaccination campaign has been largely completed in February 2022. If we rely on these preliminary results, its protective effect against infection would therefore have largely disappeared in the fall. As for protection against serious forms (and death), it would also have decreased.

Other countries had resorted to a zero Covid policy, and also ended it – all before China. New Zealand, for example, made this decision shortly after completing its vaccination campaign. Unsurprisingly, this reopening of the country has caused an upsurge in infections… but with a mortality rate limit.

Another point: Vaccination remains the safest way to protect against Covid… But new research, still in pre-publication, shows that the protection against severe forms of the severe disease is maintained a little longer after a natural infection and even longer in case of "hybrid immunity" (that is to say if a person has been both vaccinated and naturally infected).

Less in contact with Covid than the majority of other countries on the planet and less protected due to the decline in the effects of vaccination, a fairly small part of the Chinese population had hybrid immunity when the current wave began. Thus leaving the population more vulnerable.

In addition, reports suggest that the vaccination rates of the elderly (a public particularly vulnerable to Covid) in China are lower than those of the young. It would also lead to an increase in serious forms and deaths, alongside infections.

[Nearly 80 readers trust The Conversation newsletter to better understand the world's major issues. Subscribe today]

How could things evolve?

Like all previous waves, unsurprisingly, the one currently raging in China will peak before beginning its decline. But when its peak will occur, and how high it will reach, depends on the number of infections that will have actually occurred – which we don't know, due to the lack of reliable data.

A British health data company, Airfinity, has indeed estimated that since December 1, there would have been 33,2 million infections and 192 deaths… But leaked notes from a China National Health Commission meeting in late December suggest thatabout 250 million people (18% of the population) would have been infected during the first 20 days of this month! The implications in terms of epidemic dynamics of these two figures are very different.

If the true infection rates are at the upper end of the estimated values, the spike will be very high but relatively short-lived. We could therefore expect the number of cases to start falling in the coming weeks. If infection rates are at the lower end, infections on the other hand could remain elevated, with possible new spikes for some time.

In the UK, infection rates in older age groups have generally been lower than those of younger people – until recently, when infection rates in the over-60s soared past. This is partly due to the fact that, as a precaution, the elderly generally mixed less than the young at the start of the pandemic and they now stand out more. If this trend is followed in China, the country could experience continued high rates of severe disease and death even after infection rates decline.

The approaching Chinese New Year (starting January 22), the first without restrictions since the start of the pandemic (end of quarantines, etc.), also raises a lot of questions. If infections continue to grow by then, travel, family gatherings and associated celebrations will potentially further increase infection rates – and strains on already overstretched health services.

What options does China have left?

It may be too late to really alter the course of this epidemic. Estimates of virus reproduction number, or R0 (the average number of people to whom an infected person transmits the virus), are evaluated between 10 and 18 for the variants involved during this wave – which is among the highest known (along with measles).

With such a high R0, non-pharmaceutical interventions such as lockdowns, school closures, and wearing masks might not not be sufficient to control the spread of the virus.

China, on the other hand, can boost vaccination among its oldest population. It may not necessarily be too late for this to have a beneficial effect, as many of these people may still be avoiding mixing for fear of the disease and therefore have not yet been exposed.

What are the risks for the rest of the world?

Unlike China at the start of this wave hitting it, most other countries, where SARS-CoV-2 circulated widely, now have high immunity and protection in their populations against severe forms and deaths from Covid. the European Center for Disease Prevention and Control therefore noted that the Chinese situation “should not impact the epidemiological situation of Covid-19” in Europe.

Moreover, from what we know, the majority of the variants identified in China come from lines BA.5.2 and BF.7 : these lines peaked in Europe last summer and, with the development of an adapted and effective immunity, they are now declining. So any new introduction from China should not significantly increase the number of infections.

The main concern for Europe comes from elsewhere: it is the variant XBB.1.5, which quickly established itself in the United States since one month. (Always more transmissible, it is the product of the recombination of two other variants as indicated by its name in "X". It is already present in around thirty countries, including France, where it is not widely distributed at the moment, editor's note)

Of course, there is a risk that another, never-before-seen variant will emerge in China due to the large number of infections…as it might appear elsewhere in the world.

From 5 january, people traveling from China to England must take a Covid test before departure. ofother countries also adopted this approach. (Europe thus “encourages” its member states to request a negative test on boarding in China, and to supplement it with random tests on arrival. Sequencing of positive results may be recommended to identify new variants. Wastewater from aircraft toilets could also be analyzed with this in mind, such as to have an estimate of the number of contaminated passengers, editor’s note.)

But we have known since well before the Covid that the control at the entry and exit points of a country is largely ineffective to control the international spread of infectious diseases. Such screening has also proven not very useful since the start of the pandemic.

And even if border testing were effective in controlling the spread of the virus, its merit in countries like the UK or Europe – where SARS-CoV-2 and many of its variants are already circulating – would be limited.

Paul Hunter, Professor of Medicine, University of East Anglia

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

Image credit: Shutterstock / Graeme Kennedy