Covid-19: facing BA.5, will our immunity be sufficient? Not sure, say scientists

This time, doubt is no longer allowed: a new epidemic wave has got off to a good start in France. The circulation of Sars-cov-2 is accelerating, the incidence has increased sharply at the national level (+53%) and the reproduction rate of the virus is again above 1, a sign that the number of cases will continue to increase . If the BA.2 variant is still dominant, the resurgence of infections is mainly driven by the rise in power of BA.5. This new member of the Omicron family accounted for just 13.3% of cases last week. A proportion already increased to 24.2% this week. “It is certain that this lineage will very soon become dominant in our country, if this is not already the case”, assures Mircea Sofonea, epidemiologist at the University of Montpellier.

What once again lead to many deaths, and disrupt our social life? Much will depend on the strength of our immunity to this newcomer. If the experts seemed quite serene at the beginning of June, the tone is changing. This new strain is indeed more transmissible than the previous ones, with greater immune escape capacities. “Different studies, including ours, show that in the absence of a booster dose, there is almost no protection against BA.5 infection. A booster induces a response against this subvariant, but the effectiveness is less marked than against Delta or BA.1, and it decreases rapidly. Four to six months after this third dose, there are very few neutralizing antibodies against BA5”, notes Prof. Olivier Schwartz, head of the Virus unit and immunity at the Institut Pasteur. In other words, individuals who received their booster several months ago remain exposed to BA.5 infection.

Half of the population already infected with Omicron or BA.2

What about vaccinated people who would have, in addition, encountered Omicron (BA.1) or its descendant BA.2? These two viral strains circulated widely in our country, in January for the first, in March and April for the second. “It is estimated that 50% of French people have been infected by one or the other, continues Professor Schwartz. This part of the population should benefit from stronger immunity against BA.5, according to several studies published in recent weeks. and carried out using the serum of vaccinated and then infected persons”. However, the level of protection seems different depending on the sub-variant. A study led by researchers at Imperial College London and released in pre-publication, without having yet been reviewed by other scientists, shows that BA.5 is genetically closer to BA.2, from which it is directly descended, than BA.1. Prior infection with BA.2 could therefore confer more effective antibodies against BA.5. “But for the moment we still have little data with subjects previously infected with BA.2, so we don’t know”, nuances Professor Jean-Daniel Lelièvre, head of the infectious diseases and clinical immunology department at the CHU. Henri-Mondor (AP-HP) in Créteil and member of the technical committee for vaccinations of the High Authority for Health.

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The wave of BA.5 suffered by Portugal in recent weeks could have been explained, according to some experts, by the low circulation of BA.2 in this country. To which was added a declining population immunity, the wave of BA.1 already dating back to the beginning of the year. What to have the hope that BA.5 hits us less hard. But this analysis remains controversial: “The population tests itself less, so it is possible that the BA2 wave was undervalued in Portugal. Moreover, at one point, BA.2 became dominant in the samples sequenced in this country. This means that it must have circulated a lot all the same”, indicates for example Professor Antoine Flahault, epidemiologist and director of the Institute of global health at the University of Geneva (Switzerland).

If this last analysis is confirmed, we could finally find ourselves exposed to a wave of BA.5. And in fact, the rapid increase in the number of cases for a week seems to go in this direction. “The immune escape of this variant, or even its gain in intrinsic contagiousness, is added to the immune decline which reduces the protection conferred by an infection or a vaccination against a new infection, to a very low level as soon as five months. The infection is allowed again, so the conditions for a recovery resurface”, notes Mircea Sofonea. Bad news, as mortality linked to BA.5 turns out to be significant in Portugal: “There have already been 1,400 deaths between May 1 and May 15, and we can probably expect to have 2,500 to 3,000 by the end of July. For a population of 10 million inhabitants, this is significant”, specifies Antoine Flahault. Reduced to 67 million French people, this would still represent 15,000 to 20,000 deaths.

BA.5 would present a tropism for lung cells

A preprint study by a Japanese team showed that BA.5 may exhibit higher pathogenicity than other members of the Omicron family. It has indeed a mutation that was already found on the Delta variant. It would give it back a tropism for our lung cells, lost with Omicron and BA.2. “This raises questions, but for the moment it is only an in vitro signal. The epidemiological demonstration is not yet present”, nuance Mircea Sofonea. And, in fact, this does not mean that BA.5 will prove to be more deleterious than its predecessors: in those under 60 without particular risk factors, vaccination and recall continue to protect well against the risk of developing a form. severe. “The severe forms affect the most fragile, the elderly, the immunocompromised, the non-vaccinated, and in rare cases, vaccinated people, without us still knowing very well why”, underlines Professor Jean-Daniel Lelièvre .

We must therefore above all expect an “epidemic of infections”, in the words of Mircea Sofonea. However, we can fear that our social and economic life will once again be disrupted by an increase in sick leave, but to a lesser extent than at the start of the year. The seasonal brake should indeed come into play, without completely blocking the epidemic: last summer, the summer temperatures and the way of life that accompanies it (terraces, open windows, etc.) did not prevent the variant Delta to cause a wave, but it was less severe than in the fall. “Nevertheless, if the virus circulates a lot, the sick could, in proportion, be numerous to seek the care system. In a context of holidays, heat waves, closed emergencies, it could quickly become complicated, if worries Professor Jean-Daniel Lelièvre. Not to mention that many monoclonal antibodies, used in hospitals to prevent fragile patients from getting worse, no longer work against BA.5.”

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Several experts therefore call on the authorities to sound the tocsin again, at least to protect the most fragile. “If we rolled up our sleeves, we would have the means to avoid or limit the mortality of the elderly by Covid, insists Professor Antoine Flahault. “We have effective drugs, such as Paxlovid or Remdesivir, but they must be administered very early and for that it is necessary to test. But we don’t test enough. The FFP2 mask should be reimposed in nursing homes, for staff and visitors alike, but I do not hear this speech”, regrets this expert. For his part, Professor Alain Fischer hopes that once the legislative elections are over, the government will relaunch a vaccination campaign: “The alert is not very strong, but there is an alert all the same. The top priority is to ensure that the over-80s, and even the over-60s, get a second booster dose. In one week, they will be protected against serious forms”, he explains to L’Express. With a reassuring message for those who would prefer to wait until the fall: “There is no risk in repeating the doses of vaccines . On the other hand, it is essential to protect yourself now”. The weariness of the Covid should not make us forget that the threat is still there.