Covid-19: BA.5 and after, will we reinfect ourselves again and again?

Once again, the virus has thwarted the most optimistic predictions. Remember, it was at the end of 2021. Politicians, but also some scientists, saw in the arrival of Omicron our collective salvation. This highly transmissible but less “nasty” variant would infect us all without causing too much damage, and in doing so, immunize even the most recalcitrant to vaccination. With such a collective shield, no doubt: it would be the last wave. Missed.

It took just a few weeks for BA.2 to point the tip of its spicules and prove this forecast wrong. “Various publications have shown that an infection with Omicron provides little protection, explains Pr Antoine Flahault, epidemiologist and director of the Institute of Global Health at the University of Geneva. Having caught it this winter will not prevent you from further contamination. this summer. And, unlike previous variants, it does not boost immunity against severe forms.” British immunologists have even decked it out with a funny nickname: Omicron would be the “stealth aircraft of immunity”, because it passes under the radars of our defenses, leaving only a faint trace.

In the same vein, some hoped a few weeks ago that the large number of BA.2 infections in our country would protect us from BA.5. “This hypothesis was based on the fact that BA.5 is genetically closer to BA.2. But we need more data to conclude on this cross-protection between BA.2 and BA.5”, nuance now Public Health France . In the meantime, the passage of BA.2 in France did not prevent the wave carried by BA.5 from starting with a bang, with more than 90,000 daily cases on average this week. “Barring uncontrolled evolution, the impact on the hospital should remain moderate, but the number of infections will continue to increase, with significant social and economic consequences because this sub-variant causes stronger symptoms than the previous ones. “, says Professor Mahmoud Zureik, epidemiologist at the University of Versailles Saint-Quentin-en-Yvelines.

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Towards an eighth or ninth season of the Covid?

SARS-CoV-2 therefore seems far from finished with us. Contrary to widely held ideas, it is not currently proving to be either seasonal or endemic. Worse, it is capable of reinfecting us at regular intervals, thanks to the appearance of new variants or the weakening of our immunity. So, like a bad television series, should we expect an eighth, a ninth, a tenth season, or even more? For epidemiologist Mircea Sofonea, there is little doubt. With Bastien Reyné, doctoral student within his team at the University of Montpellier, he carried out a modelization up to 2025 of hospital admissions for Covid, distributed in prepublication (without having yet been reviewed by other scientists). “It is not a question of providing predictions to the unit, but of comparing the impact of different strategies for managing the epidemic”, he warns.

The main lessons of his study are hardly encouraging. “In the total absence of measures, we expect to have more hospitalizations in the coming years than in 2021. As for vaccination, it will not, on its own, reduce the impact on the establishments”, explains the researcher. His work is based on recent British data on the evolution over time of the effectiveness of boosters, both against infection and against hospitalizations: “They show that after five months the effect of an additional dose or a reinfection fades. This means that every five months there is a reconstitution of a population susceptibility which allows an epidemic resumption”, explains the scientist. It is therefore not even necessary for a new variant to arrive to see the number of cases start to rise again: “If there had not been BA.4 and BA.5, we would probably have had another wave of BA.2 a little later,” says Mircea Sofonea.

To make a difference and limit hospitalizations, it would be necessary, in addition to vaccination, to reduce the circulation of the virus by at least 20%, according to his model. “Vaccines have allowed us to get out of confinements and curfews, but they are not enough to move on to a new phase of the pandemic where we would no longer see these iterative waves”, confirms Antoine Flahault. The proof, for this expert, the mortality linked to Covid is still very high, despite the injections: still more than 59,000 deaths last year against 64,000 in 2020, according to the National Institute for Demographic Studies (INED), and already more than 23,000 deaths from January to the end of June 2022, according to data from Public Health France.

“Repeating that the epidemic is over becomes counterproductive”

“We need a major ventilation plan for closed places, to limit transmissions. Until we launch it, we will not get out of it”, repeats Professor Flahault, in unison with all the specialists of the Covid. The unknowns around the cumulative effect of multiple reinfections are not the least of the reasons to try to avoid getting infected again and again. “Are they less violent, or, on the contrary, do they increase the risk of having a severe form or a long Covid? For the moment, we do not know much about it”, admits Professor Zureik. The question arises all the more acutely as various studies suggest a drop, modest admittedly but a drop all the same, in the protection conferred by reminders against serious forms. Recent Israeli work on 40,000 people over the age of 60 has shown that after four months the fourth dose only provides 72% protection against death. “It remains very high, but we are no longer in the golden age of efficiency exceeding 90%”, notes Mahmoud Zureik.

At the same time, vaccines adapted to the evolution of the virus are long overdue. “Bivalent” injections, with the original virus (Wuhan) and a strain of Omicron, are proving complex to develop. “It is difficult to choose the sub-variant to include: BA.1 is no longer so useful, but nothing says that in the fall BA.5 will still be in circulation. Manufacturers risk finding themselves in constantly running after the virus”, worries Bruno Canard, research director at the CNRS and virologist at the University of Aix-Marseille. However, the more Sars-CoV-2 circulates, the greater the risk of seeing variants emerge. “Most likely is that there are newcomers to the Omicron family. Another scenario would see our immunity to previous strains, like Delta, weaken. One of them could then redeploy from a reservoir that would have escaped surveillance”, imagines the coronavirus specialist. Unless the virus makes a detour in immunocompromised people or in animals, and it comes back in a new form.

“The real subject is the management of scientific uncertainty. Caution should be imposed: repeating each time the epidemic ends becomes counterproductive, because the general relaxation after a wave contributes to the appearance of the next,” laments Mahmoud Zureik. The only certainty: we will continue to need all the weapons at our disposal. Masks, ventilation, new generation vaccines, drugs… “We can hope for the arrival at the end of the year of antivirals capable of mitigating the impact of an infection or of being administered as prophylaxis for contact cases. , which would help to cut the chains of transmission”, underlines Bruno Canard.

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The end of confinements and curfews may have led people to believe that the pandemic was behind us. The arrival since then of successive waves shows that it would be wrong to continue to underestimate this virus.