We still don’t know to what extent Covid vaccines stop transmission


SARS-CoV-2 could cause its deadliest damage to the lungs, heart and blood vessels. But its first stop in the human body is usually the nose, as this is where inhaled virus particles first encounter cells that they can invade and hijack in order to reproduce. From there, the swarm of new viruses can spread to other organs – if the immune system doesn’t stop them. And it is from the nose that infected people can send new clouds of contagion.

So, for a vaccine to completely block transmission, one would have to recruit a distribution of antibodies and immune cells targeting SARS-CoV-2 specifically to patrol the nasal passages, where they could glomerate on just about any coronavirus. after being inhaled, and before they start their self-replicating frenzy. This is how nasal spray versions of influenza vaccines work. But that’s just not what Pfizer’s or Moderna’s plans were designed to do. They were designed to create a more sparse team of larger traveling immune defenders who can elicit a larger response wherever they encounter the virus, giving an infected person a better chance of fending off symptoms on their own. “The purpose of these vaccines has always been to prevent people from being hospitalized and dying, because this has the greatest impact on public health,” says Talaat.

The good news about the Israeli and British studies, even with their methodological flaws in transmission, Talaat says, is that they show that in the real world, far from the controlled parameters of a clinical trial, vaccines work fabulously to prevent people. to become seriously ill. In the leaked Israeli report, vaccines led to a 95% drop in hospitalizations and 92% in deaths. And more recent and better controlled data is already starting to support this.

A study published Wednesday in the New England Journal of Medicine who analyzed 600,000 pairs of vaccinated and unvaccinated Israeli individuals found that two doses of the Pfizer vaccine were 92 percent protective against serious illness and 87 percent effective in preventing hospitalization. Although the study did not have data on deaths after the second dose, a single shot reduced death rates by 72%. So from a public health perspective, that makes the question of whether the Pfizer vaccine, or any other vaccine, to stop the viral spread, is really a secondary concern, Talaat says. “If you get enough people vaccinated, you don’t need a vaccine that stops nasal carriage and potential transmission,” she says.

But this number matters in answering questions like these: Is it safe to eat in a restaurant? Or get on a plane? Or hug your grandchildren?

Suppose the vaccine you receive is 80% effective in blocking the spread of the virus. This means that if you contract the virus you may not get seriously ill or even have a single symptom, but there is still a 20% chance that you will pass it on to someone else. What if the vaccine you receive is only 50% effective in blocking the spread? Now it’s a draw.

“This is exactly the type of gray area where reasonable people could reasonably come up with different answers,” says Halpern. “It all comes down to the fact that we don’t all have the same tolerance for risk.”

Talaat’s version of this calculation involves navigating family reunions with his parents (vaccinated) and siblings (unvaccinated). Since she is vaccinated herself, Talaat always wears a mask when visiting her siblings. And she will continue to do so until they get their shots. But she feels more relaxed with her parents. “If you are in a household or capsule with someone who is not vaccinated, you should always be as careful as possible to avoid potential transmission, especially if that person is at high risk,” she says.

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