NEW: The herd immunity threshold for the coronavirus will stay out of reach, because widely circulating variants and persistent hesitancy about vaccines. The virus is here to stay, but vaccinating the most vulnerable may be enough to restore normalcy.…
First, let's be clear what we're talking about. "Herd immunity" just describes the level of immunity in a population, whether that's 10% or 70%. What we're talking about in this article is the herd immunity threshold -- at which the virus stops being able to cause big outbreaks.
We thought it was maybe 60-70%, some even suggested 20-30%, but it's increasingly likely that we will need about 90% because of more contagious variants (herd immunity depends on R0, the measure of contagiousness).
But the good news is we may not need to reach the herd immunity threshold. What really matters is the number of hospitalizations and deaths. If we can keep those low enough by vaccinating the highest risk people, we can turn the coronavirus into a manageable threat.
This is a shift in thinking -- and perhaps a jarring one at first. But it's important to remember that the goal is still to vaccinate as many people as possible so we can get as close as possible to the herd immunity threshold, and minimize hospitalizations and deaths.
Some people will argue we're already at the herd immunity threshold. Look at Israel, they'll say. Israel has brought numbers down with vaccines, but without reaching the threshold, and the virus has temporarily been managed. We've learned this lesson many times over.
What about natural infection, you ask? Natural infection plays a role but neutralizing antibodies in many infected people do stop after a while. T cells, while they can mitigate symptoms, do not prevent infection, which is what we need to reach herd immunity threshold
One more thing about natural infection: All evidence so far suggests that vaccines put up a stronger defense against variants. At some point, we'll need boosters for everyone to keep up with variants, so no, natural infection will not carry us the whole way.
With many thanks to the scientists who spoke to me: @mlipsitch @nataliexdean @laurenmeyers @CT_Bergstrom @BaryPradelski @mcpoliti
Rustom Antia, Tony Fauci, David Morens, Jeffrey Shaman, Betz Halloran and Virginia Pitzer

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More from @apoorva_nyc

23 Apr
ICYMI: Pfizer and Moderna should work well against B.1.526. This is good news for just about any vaccine with the E484K mutation…
I say just about because it depends on what else a variant has. B.1.351 (the one seen in South Africa) also has E484K and shows the same drop of about 4-6 fold in neutralization, which won't be a lot when the efficacy is as high as it is with Pfizer and Moderna
But P.1, the one circulating in Brazil, doesn't seem to have that edge over vaccines, despite having E484K. We don't know what the case is for newer variants like B.1.617 and also don't have good info on other vaccines against these variants
Read 5 tweets
23 Apr
BREAKING: The Pfizer-BioNTech and Moderna vaccines will effectively prevent serious illness and death from B.1526, the variant circulating in New York, two independent studies suggest.…
In lab studies, with psuedovirus, there is a four- to six-fold drop in effectiveness, just as with the B.1351 variant found in South Africa. That's not surprising because both have the E484K mutation.
But in a real-life setting, the Pfizer and Moderna vaccines will work. I'm specifying which ones because those are the ones tested. The others (J&J, AZ) will probably also work, but they start out with lower efficacy, so it would be good to see data.
Read 5 tweets
15 Apr
NEW: In our celebration of vaccines, let's not forget the millions of people who are immunocompromised. Many of them produce few to no antibodies in response to a vaccine or an infection, leaving them susceptible to the virus. 1/5…
What do we mean by immunocompromised? It turns out to be a startlingly big group: survivors of blood cancers; organ transplant recipients; anyone who takes Remicade for IBD or Rituxan, Gazyva or Imbruvica — which block antibody-producing B cells; some people over 80. 2/5
Most people who have lived with immune deficiencies for a long time are likely to be aware of their lack of response to vaccines. But others have no idea that medications may have put them at risk. 3/5
Read 5 tweets
13 Apr
The pandemic has hit many groups of people particularly hard, and one of those is women -- including women in #STEM. #WomenInScience #sciencetwitter…
With minimal support from their institutions and the burdens of pandemic stress, compounded by childcare and racism for some, many women may be forced to leave science for good.
For many women in science, social media (yes, even Twitter), has been a source of support, and strength to push back against patriarchy -- to decry sexist papers or to take down a #dudewall (which is exactly what it sounds like)
Read 4 tweets
3 Apr
NEW: The world is caught in a sprint between vaccines and variants, and the shots eventually will win, scientists say. But it is increasingly clear that the next few weeks is likely to be painful.…
For weeks, the mood in much of the United States has been buoyant. Cases, hospitalizations and deaths from the coronavirus fell steeply from their highs and millions were being vaccinated every day. But as experts predicted, the curve has begun to swing upward again. 2/4
For how long? and how high will it go this time? That's not clear. But scientists are worried that B.1.1.7 and other variants will cause another surge and, over the long term, require people to queue up for regular rounds of booster shots. 3/4
Read 4 tweets
1 Apr
NEW: @CDCgov walked back controversial comments made by @CDCDirector Dr. Rochelle Walensky, suggesting that people vaccinated against the coronavirus never become infected or transmit the virus to others…
@CDCgov @CDCDirector As @10queues said: “We’re stopping symptoms, we’re keeping people out of hospitals. But we’re not making them completely resistant to an infection.”
@CDCgov @CDCDirector @10queues Why does this matter? Because the vaccines are excellent, but they're not perfect. All the vaccines prevent serious illness and death, but they do not prevent infection, and they may not prevent transmission
Read 4 tweets

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