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Why Johnson & Johnson’s one-shot Covid-19 vaccine is a game changer

The vaccine is very effective — and most importantly, it only requires one shot.

A pharmacy technician holds a dose of the Johnson & Johnson Covid-19 vaccine before it’s used for a clinical trial on December 15, 2020, in Aurora, Colorado.
Michael Ciaglo/Getty Images

One big reason to be excited about the new Johnson & Johnson vaccine for Covid-19, which was authorized by the Food and Drug Administration over the weekend for emergency use in the US: Unlike the Moderna and Pfizer vaccines already in use, it requires only one shot for full protection.

That’s a big deal. From a practical standpoint, it means that the new vaccine could really speed up America’s vaccination campaign — certainly more than another two-dose vaccine would. It also fixes a problem that’s long bedeviled medical treatments that require multiple doses: A lot of patients tend to drop off after the first appointment.

“Especially when you’re trying to think about a massive public health program like this vaccine rollout, a single-dose vaccine would have made it much, much simpler” if it were the first to get approval, Amesh Adalja, a senior scholar at the Johns Hopkins Center for Health Security, told me.

Some have been skeptical of the Johnson & Johnson vaccine because the reported data on its efficacy was lower than that from the Moderna and Pfizer vaccines. Initially, the vaccine was reported at 66 percent effectiveness against Covid-19, which paled in comparison to 90-plus percent for the other two authorized vaccines.

But in many ways, that’s looking at the wrong number. The vaccine’s effectiveness at preventing people from getting sick with symptoms is arguably much less important than the vaccine’s effectiveness against hospitalization and death. And there is the promising news: In trials, the Johnson & Johnson vaccine brings both of those down to zero. It squashes the biggest thing that made Covid-19 so threatening to people: its ability to kill.

Given the ongoing supply constraints and high demand, experts say people should get whichever vaccine is first available to them — that’s how we’ll beat Covid-19 as quickly as possible.

But for people who are bad at follow-up appointments (including me) and from a broader public health perspective where speeding and smoothing the vaccine rollout is crucial, the Johnson & Johnson vaccine and other one-shot inoculations are genuine game changers.

1) The one-shot vaccine we have is really effective

In non-pandemic times, Americans deal with common infectious illnesses that don’t force society to shut down schools, businesses, and other interactions with people outside our households. Nobody likes getting the common flu or cold, but because most of us don’t expect it to hospitalize or kill us, we by and large just live with them. (Though, seriously, more people should get their flu shots — that would still save lives.)

This is the marvel of the Covid-19 vaccines approved so far: They turn the coronavirus into something much more manageable, like a cold or flu. Some people who get the vaccine may still develop sniffles or even a fever if the virus infects them. But based on the clinical trial and some real-world data, the risk of severe illness, hospitalization, and death drops massively — to zero or almost zero, particularly for hospitalizations or deaths.

The Johnson & Johnson vaccine is no different in this regard. According to data released by the FDA last week, the clinical trials found an efficacy rate of about 72 percent in the US. But that’s the number that only tells us about any symptomatic infection, down to the sniffles or a short-lived fever. For hospitalizations and death, the Johnson & Johnson vaccine reported 100 percent effectiveness after 28 days (all of the vaccines so far take weeks to build up the body’s defenses).

So Johnson & Johnson’s vaccine might not be as effective as the competition against the milder symptomatic cases, but it’s as effective for the kinds of illnesses that make Covid-19 truly scary.

“I would take it,” Jen Kates, director of global health and HIV policy at the Kaiser Family Foundation, told me. “A lot of us who look at the data say we would definitely take a vaccine that’s that effective.”

One of the big concerns right now is whether the vaccines work against Covid-19 variants. There, too, is good news: Johnson & Johnson ran part of its trials in South Africa, where the variant with the most confirmed effect on immunity has shown up. The vaccine still worked, with a 64 percent overall effectiveness against any symptomatic disease and 100 percent effectiveness against hospitalization and death.

There are still some genuine unknowns about the vaccine. We don’t know how much it stops the spread of the disease, although the early data suggests it likely has at least some effect. Some of the data indicated the vaccine might not be quite as effective among older populations with comorbidities like heart disease or diabetes, but the sample size was too small to draw hard conclusions.

For the vast majority of people, though, the Johnson & Johnson vaccine does exactly what you would want it to do: It makes it so Covid-19 is no longer deadly — the kind of pathogen you can give as much thought to in any given year as a common flu or cold.

2) A vaccine that doesn’t require follow-up is a big deal

In health care, simply getting people in the door can be the first big hurdle. People in need might not have health insurance or be able to afford care. Even if they have insurance, they can have other problems — inconsistent transportation or an inflexible job schedule — that make them less likely to end up at a doctor’s office. Or people might think too much of their own health because they’re young and fit, or they might not like going to the doctor.

This is a well-known problem in public health. For some people, getting multiple doses of a treatment is “a lot,” Saskia Popescu, an infectious disease epidemiologist at George Mason University, told me. “That’s why it’s really hard to get people to get their full hep B vaccine.”

Studies back this up. As Dylan Scott wrote for Vox:

[B]ased on research that evaluated compliance with other multi-dose vaccines, patients are really, really bad at getting their second dose. Bad as in, as many as half of patients never do. Studies conducted in both the US and UK on the hepatitis B vaccine — which, like the Covid-19 vaccines, is supposed to have around a one-month period between the first and second doses — found that roughly 50 percent of patients failed to get their follow-up shot within a year after their first.

Maybe the numbers will look better for the Covid-19 vaccines. The stakes of a deadly pandemic are much higher, and perhaps people will react accordingly. But if a significant number of people fail to get their second shots, and the first dose of Moderna’s and Pfizer’s vaccines proves to not be enough, that could doom the prospects of herd immunity, when enough of the population is vaccinated to stop the spread of the virus.

On the flip side, some people may simply be unable to schedule a follow-up appointment, especially as supply and distribution problems with vaccines persist. This will likely become less of a problem over time, as the vaccine rollout steadily expands and improves. But in the meantime, it creates an additional risk of people missing their second shot.

All of this is no longer hypothetical. In the US, about 14 percent of the population has gotten the first dose of a Moderna or Pfizer vaccine, while just 7 percent has gotten the second dose, according to the New York Times. Some of this is because the rollout is still in its early stages, but nearly 3 million Americans haven’t received their second vaccine doses on time.

How much the gap between first and second doses closes — or widens — will show the need for Johnson & Johnson’s vaccine and other one-shot vaccines.

3) A one-shot vaccine could really speed our path to herd immunity

One of the most obvious benefits to a one-shot Covid-19 vaccine is it could dramatically speed up — literally double — the US’s vaccine rollout.

Over the past couple of weeks, America has hovered around 1.5 million vaccine doses a day. That number had been steadily climbing until the recent snowstorms, which temporarily slowed things down. But imagine the US somehow gets stuck at the current rates.

Under that scenario of 1.5 million doses a day, the requirement for two shots means the US wouldn’t get to a threshold of herd immunity of 80 percent — a number that could be too high or too low; we just don’t know yet — until spring 2022.

But if the US somehow replaced all its vaccines with a one-shot vaccine — not at all likely, but it’s helpful for demonstration purposes — the current pace would be enough to reach herd immunity toward the end of summer. In a more realistic scenario, where one-third of vaccines are one-shot, the US would reach herd immunity by the end of this year.

Now imagine that the US manages to get to 3 million shots a day (which no longer seems unlikely). At that rate, two-dose vaccines would get us to herd immunity at the end of the summer, and a one-shot–only approach would get us there before summer. If one-third of vaccines are one-shot versions, we reach herd immunity by mid-summer — leaving the rest of the summer to, hopefully, live much closer to normal than the last year.

You shouldn’t take these numbers too seriously. We don’t know, because we don’t have a crystal ball, how much the US vaccination campaign will ramp up in the coming months. We don’t know how much Johnson & Johnson, which has already reported manufacturing problems, will scale its vaccine production from the 20 million the company promised by the end of March to the 100 million it promised overall. We don’t know if the 30 percent of Americans who currently report vaccine hesitancy will remain hesitant, which would doom the prospects of herd immunity. And we don’t yet have a vaccine authorized for use in children — and since those under 18 make up about 20 percent of the population, that could also ruin the chance of herd immunity.

But the numbers, at least, demonstrate the potential of a one-shot vaccine like Johnson & Johnson’s. It could speed up the vaccination process in the US by weeks or even months.

With thousands of people still dying every day from Covid-19, that boost could translate to upward of tens of thousands of lives saved.

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