Waning Immunity Is Not a Crisis, Right Now - The Atlantic
▻https://www.theatlantic.com/science/archive/2021/09/waning-immunity-not-crisis-right-now/619965
Doser les #anticorps chez les vaccinés (ou anciens infectés) en dehors d’une période de contact avec le virus donne un faux aperçu du statut immunitaire :
Checking someone’s #SARS-CoV-2 antibody levels when there’s no virus around can be a bit deceptive, […]. In the absence of a threat, immune cells are quiescent. But the capacity for protection remains intact: When new invaders arrive, they’ll reawaken our defenses. That’s why post-vaccine infections, when they do happen, tend to be milder, shorter, and less likely to spread to other people. When the new threat resolves, levels of antibodies and active immune cells decrease again. “You could call that ‘waning,’” Pepper, of the University of Washington, told me. “But that’s just how it works.”
Mais il arrive un moment où l’immunité finit quand même par disparaître :
Immune memories don’t last forever. Eventually, even the grizzled B and T cells in the body’s reserves might permanently retire. That’s when protection against disease and death could start to take a tumble, and when experts start to get worried.
Pour certains experts il faudrait multiplier les rappels de #vaccins pour empêcher cet épuisement :
Some officials, including CDC Director Rochelle Walensky, have suggested that upticks in post-vaccine coronavirus infections are a sign of what’s to come, and that giving people extra shots could be a way to jog the immune system’s memory before it fades away.
The same rationale applies to many multi-dose vaccines: The first shot introduces the body to the notion of a threat; the ones that follow clinch the concept that the danger is real and worth taking seriously. A triple-jab regimen is already built into several well-established vaccines, including the ones that block HPV and hepatitis B; others require four or five inoculations before they take.
Mais, pour la plupart des experts et pour différentes raisons, cela semble incertain sinon douteux pour le sars-cov2 :
But according to most of the experts I spoke with for this story, the immunological argument for a COVID-19 booster this early is shaky at best.
To start with, the recent numbers on vaccine effectiveness aren’t really that alarming. Vaccinated people are indeed getting infected with SARS-CoV-2 more frequently than they were a few months ago. But these breakthroughs remain fairly uncommon. Recent reports from the CDC show that the Moderna and Pfizer-BioNTech vaccines were blocking infection at rates of up to about 90 percent in the spring, when the vaccines had barely begun their rollout en masse; now those stats are hovering around the 60s and 70s, still a remarkable feat. (That doesn’t mean that 30 to 40 percent of vaccinated people are getting infected; rather, immunized people are 60 to 70 percent less likely than unimmunized people to be infected if they’re exposed.) Numbers from other studies look to be in a similar ballpark. And these stats might even undersell the vaccines’ benefits: Many “infections” are found simply through the detection of viral genetic material—with no guarantee that this material is active, infectious, or anything more than the carnage left behind from a victorious immune attack.
The outlook is even better when you consider symptomatic cases of post-vaccine COVID-19. Early reports, including Moderna’s and Pfizer’s original study estimates, put the vaccines’ efficacy against symptomatic illness in the range of 90 to 95 percent. More recent studies now document rates in the 80s, even when facing off against Delta—a variant for which the vaccines weren’t originally formulated.
Certaines constatations en faveur d’une multiplication des rappels seraient biaisées :
Some reports from Israel appear to paint a more dire portrait: A few preliminary numbers released by the country’s Ministry of Health suggested that vaccine effectiveness against both infection and symptomatic disease had dipped to about 40 percent. But Çevik, of the University of St. Andrews, told me that these and other data reporting heftier declines are messy and might actually overestimate the problem. Across countries, early vaccine recipients tended to be older, in slightly worse health, and in higher-risk professions than those who got injected later on. That alone could make the protection that they got seem less impressive in comparison. Also, when initial effectiveness numbers were calculated, people were adhering more to physical distancing and masks. Measured these days, amid more lax behavior, risk of infection would rise. And as more of the unvaccinated have been infected, their collective immunity has grown, making them, too, less susceptible to the virus—which could make the effectiveness of vaccines look lower.
Il faut distinguer #protection contre l’infection de protection contre l’hospitalisation et la mort ;
“The point isn’t to protect you from getting even a tiny amount of virus in your body,” she said. We’re not out to eradicate positive test results: “That’s not what vaccines do.”
Si l’utilité de la multiplication des rappels est incontestable dans certains cas… :
As for boosters, the pros and cons will vary by context. For people who never responded well to their first vaccines, including people who are moderately or severely immunocompromised, additional shots will be very important, Omer said. Their third jabs don’t provide an extraneous “boost” so much as they help complete the original inoculation schedule.
… cette utilité est incertaine dans les autres cas :
For the rest of us, though, the perks are harder to visualize. In someone with a fully functional immune system whose defenses were already substantially shored up by their first shots, more doses would probably increase antibody production. That, in turn, could further cut down on infection and transmission, Gommerman told me. Very early data hint that this may be happening in Israel, which is already boosting widely. But it’s not clear how long that preventive bump would last . Ellebedy, of Washington University in St. Louis, said boosters would have “real gain” only if they expanded on the body’s capacity to manufacture antibodies long term, instead of just fueling a temporary boom-and-bust . It’s especially unclear whether that would happen with yet another injection of the original vaccine recipe, delivered to the arm—as opposed to, say, a nasal spray with Delta-specific ingredients.
En conclusion, en l’état actuel de la pandémie et des connaissances, la multiplication non sélective des rappels se ramène à verser de l’eau dans un verre déjà bien rempli… :
Right now, some forms of vaccine effectiveness are slipping, but the most important ones aren’t. Unless that changes, widespread boosters in already vaccinated countries are likely to provide diminishing returns, like topping off a drink that’s already on the verge of spilling over.
… et pire encore à favoriser l’émergence de nouveaux variants en privant les pays pauvres de lots de vaccins :
In the meantime, billions around the globe have yet to take a sip at all.
#immunité
