| Hey readers, The news on the Covid-19 vaccine front of late has been quite good –– perhaps so good that our perspective on the fight against the pandemic may be getting a little warped. Case in point: the Johnson & Johnson vaccine. Results from its trials were released last week, and the company filed Thursday for FDA emergency use authorization. According to the company, it should be able to deliver 100 million doses to the US in the first half of this year. But this good news hasn't been greeted with the enthusiasm that greeted Pfizer and Moderna. Perhaps that's because in its clinical trial, the J&J vaccine had an efficacy number (the percentage of cases prevented entirely) of 66 percent. Compared against the 95 percent efficacy rate for the Pfizer vaccine and the 94.1 rate for Moderna's, you can kind of understand why the response would be a little more muted. But if you dig deeper into the numbers, the J&J vaccine is still a tremendous new weapon in our arsenal. That's because it makes Covid-19 cases much milder –– meaning you might still get sick, but you are much less likely to be hospitalized or die. Indeed, while the data is not perfectly comparable, the J&J vaccine seems to perform just as well in preventing severe illness as Pfizer's and Moderna's, a fact that seems to have been undersold in news coverage. To put J&J's effectiveness in another context, think about the flu. Flu vaccines mostly don't prevent you from getting sick with the flu but instead make the flu much less awful if you catch it. And at-risk populations –– the very young and the very old –– are much less likely to die of it. That's still a very good outcome! A Covid-19 vaccine that was similar to that –– one that made you much less likely to be hospitalized or die, and made the virus milder –– would still be enough to bring the pandemic to an end and give us back our lives. That's exactly what we have with the current crop of vaccines. No one who's got two doses in clinical trials for the Moderna and Pfizer vaccines has been hospitalized or died. The same holds true for the new, unapproved vaccines from Johnson & Johnson, Oxford/AstraZeneca, and Novavax. Each of the vaccines has demonstrated very high protection against severe Covid-19 in their trials –– protection that is not statistically distinguishable from being totally perfect. So why aren't we talking about that? How "efficacy" became the measure of vaccine success There's a reason headlines have focused on the efficacy of preventing all disease rather than severe disease: It's what the earliest clinical trials were set up to primarily study. If you want to estimate the frequency of hospitalizations and deaths, you need a really big study, because estimating the frequency of rare events requires tons of data. (For all the big numbers we're seeing in hospitalizations and deaths, they actually still count as relatively rare events compared to cases.) I noted above that there have been zero cases of hospitalization or death in clinical trials for all of these vaccines, but that does not mean that they're perfect at preventing hospitalization or death. These clinical trials were already long, slow, and expensive. The companies running them picked measurable results that didn't need an even bigger trial to confirm for sure. So they focused on positive Covid-19 tests prevented. And they got some great results! But the most important thing here isn't necessarily preventing cases –– it's preventing transmission and severe illness and death. The vaccines appear to do that too! But as a consequence of how the first trials were conducted and reported, this fact about them –– the one more relevant in driving down the death toll and getting life back to normal –– has gotten much less attention. This shift in focus has real consequences. The Johnson & Johnson, AstraZeneca, and Novavax vaccines have lower efficacy at preventing all Covid-19 cases, but we have reason to think they're just about as good at preventing hospitalization and death. And yet there's widespread sentiment that they're worse, and that it's okay that the US isn't expediting their approval and distribution because people would rather get the better vaccines anyway. This line of reasoning would be understandable if some vaccines are 95 percent effective at preventing hospitalization and death and some are only 60 percent effective, but it's a mistake when all of the vaccines are indistinguishably effective by this metric. This is a huge communications challenge for the media –– and not one with an easy solution. Reporting that a vaccine is 95 percent effective at preventing disease is much easier than explaining something like: "The vaccine is extremely effective at preventing severe disease, though that wasn't the primary clinical trial endpoint. And it's a rare enough event that we can't tell the difference between 99 percent and 100 percent effectiveness yet." Furthermore, it's not wise to overpromise by overhyping the "zero hospitalizations, zero deaths" stat –– inevitably there will be some deaths even in the vaccinated group. (Now that 700,000 people in Israel have been vaccinated with the Pfizer and Moderna vaccines, there have been a few hospitalizations –– 16, to be precise, for a rate of .002 percent). I can sympathize with the challenge of communicating these complexities. But we have got to get this right. The Johnson & Johnson, AstraZeneca, and Novavax vaccines, and the public embrace of them, might make a huge difference on whether things start to get back to normal in the US in April or in August. And that's a difference of hundreds of thousands of lives potentially saved. ––Kelsey Piper, @kelseytuoc | 
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