The United States, Italy, Japan, India, Malaysia… The list of countries that have announced reinforced border controls for travelers from China continues to grow. All share the same fear: that the outbreak of Covid cases in this country will eventually bring out new variants which would relaunch waves of hospitalizations and deaths in our regions. However, the question is still much debated in the scientific community. Because with an extremely contagious virus left free to spread in a population of 1.4 billion inhabitants with very little immunity, we are once again faced with an unprecedented situation. “Advancing on the possible consequences for the rest of the world is all the more difficult as we have very little information on the extent of the Chinese epidemic or on the variants that feed it”, notes the epidemiologist Mahmoud Zureik, professor at the University of Versailles Saint-Quentin-en-Yvelines.
That the virus continues to circulate on such a large scale is of course not good news. “When it spreads intensely, mutants will appear naturally. Many disappear because they prove to be less competent. But from time to time, this can give rise to more problematic variants”, recalls Etienne Decroly, virologist at the University of Aix-Marseille. But should we therefore fear the emergence of variants against which we would not be protected at all? As always in a new context, the uncertainties are great, and the data to be taken into account numerous. Some factors could play in our favour, in particular the low level of herd immunity in China, due to a deficient vaccination campaign and the absence of circulation of the virus since the first wave in Wuhan. “It is the immune pressure that pushes a virus to evolve in order to escape antibodies. However, in China, there is no immune pressure. The most probable hypothesis is therefore that the virus will not experience any significant development in the short term”, indicated on several occasions in recent days Professor Bruno Lina, virologist and member of Covars (Committee for monitoring and anticipating health risks, which replaced the Scientific Council Covid-19).
“Bad surprises cannot be ruled out”
In Europe as in the United States, the waves of the last few months have been carried by variants with increasingly important immune escape: “The virus will continue to evolve, but it will not need to go into this direction, at least in the short term. As long as its variants remain in the Omicron family, even with ever-increasing transmissibility, they are unlikely to break out of China and become dominant in other countries, where the protection conferred by previous infections and by vaccination is much stronger,” confirms T. Ryan Gregory, an evolutionary biologist at the University of Guelph in Canada. And in fact, the sub-variant of Omicron BF.7, which seems to circulate strongly in the country, has so far failed to establish itself in Europe or the United States, whereas it had been there. spotted several weeks ago. “At this stage, adds the Canadian scientist, a sub-variant like XXB 1.5, endowed with both significant immune escape capacities and great ease in infecting our cells, worries me more”. And this newcomer didn’t need China to point the tip of its spicules…
“Unpleasant surprises from the Middle Kingdom cannot, however, be ruled out,” worries Professor Zureik. Several scenarios could indeed lead to the appearance of more dangerous microbes, because they would have evolved into a very different form, much like when Alpha, Delta or the first member of the Omicron family appeared. Experts speak of “evolutionary divergence”. To do this, for example, the virus would have to make a detour to another species. Some scientists suspect Omicron to have emerged in this way: it first evolved in infected mice, which in turn infected humans. Another possibility: that the virus infects an immunocompromised person. We know that in this case, the infection lasts a long time, which gives the virus the possibility of acquiring a very large number of mutations. Alpha, among others, would have appeared this way.
“We don’t have a crystal ball”
Finally, there could be recombinations between variants. This is what happens when two different viruses infect the same host. “In this case, the genetic difference with the strains in circulation can become large enough that immune control is less effective. We know this process very well in influenza: the virus responsible for the Spanish flu epidemic in 1918 is appeared in this way, following a mixture between two strains of influenza virus. Fortunately, these are rare events”, decrypts Etienne Decroly. Different Sars-CoV-2 recombinants have already emerged, so far without much impact on the epidemic – but that does not mean that it will always be the case. “An Omicron recombinant with a more virulent virus would be the worst-case scenario,” says Ryan Gregory.
Of course, the more the virus will circulate, the more the risk of seeing such an accident occur will increase. “But we don’t have a crystal ball: the reality is that it remains very difficult to predict which variations can be selected, such as whether they will be problematic or not. This must therefore remain a point of vigilance important for the health authorities”, insists Etienne Decroly. In fact, if the European Center for Disease Prevention and Control considers border tests “unjustified”, many scientists insist on their necessity. Above all to find out more about the Chinese situation, in the absence of official information: “We need an ambitious policy of sequencing the PCR tests of travelers from China, to better understand the viruses circulating there and detect possible new variants that could appear there”, defends Professor Mahmoud Zureik.
On the other hand, it is useless to hope that this could prevent their dissemination: “It could only slow down their arrival. Moreover, the measures proposed by certain countries are perhaps above all intended to put pressure on the Chinese authorities so that they communicate more on what exactly is happening in the country”, notes Yannick Simonin, professor of virology at the University of Montpellier. Because without real transparency on the part of Xi Jinping’s government, we risk, unfortunately, finding out at one time or another at our expense. And again too late.