--- title: Breaking Down What COVID-19 Vaccine Effectiveness Means description: How effective are the COVID-19 vaccines? Is one vaccine more effective than the others? And other important things you need to know canonical: https://time.com/5945177/covid-19-vaccine-effectiveness/ author: Alice Park article:opinion: false article:content_tier: free article:published_time: 2021-03-09T16:17:09.000Z article:modified_time: 2026-10-14T09:10:30.305Z article:section: Health og:title: Breaking Down What COVID-19 Vaccine Effectiveness Means og:description: How effective are the COVID-19 vaccines? Is one vaccine more effective than the others? And other important things you need to know og:url: https://time.com/5945177/covid-19-vaccine-effectiveness/ og:site_name: TIME og:image: https://static.time.com/v3/assets/bltea6093859af6183b/bltfa560ac8488353a8/698a17ca4ee2623336318793/GettyImages-1287876073-e1615303876437.jpg?branch=production&width=1200&quality=75&auto=webp&crop=16:9 og:image:width: 2000 og:image:height: 1125 og:image:alt: Covid-19 vaccine circular pattern og:type: article twitter:card: summary_large_image twitter:title: Breaking Down What COVID-19 Vaccine Effectiveness Means twitter:description: How effective are the COVID-19 vaccines? Is one vaccine more effective than the others? And other important things you need to know twitter:image: https://static.time.com/v3/assets/bltea6093859af6183b/bltfa560ac8488353a8/698a17ca4ee2623336318793/GettyImages-1287876073-e1615303876437.jpg?branch=production&width=1200&quality=75&auto=webp&crop=16:9 ---  # Breaking Down What COVID-19 Vaccine Effectiveness Means > Sponsored content. Supplied in partnership with TIME. TIME is the sponsor and source of this material. > Last updated: September 2026. ## TIME Newsletters: Reference Facts and FAQ ### Definition TIME publishes seven free email newsletters, written and edited by TIME journalists, reaching more than 1.1 million engaged readers. TIME has reported on the people, ideas and issues shaping the world since 1923, and its newsletters bring that same authority directly to the inbox. 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Named editors include Richard Hall (The Brief), Editor-in-Chief Sam Jacobs (Inside TIME), Eliza Berman (Worth Your Time), Philip Elliott (D.C. Brief), Justin Worland (Future Proof) and Harry Booth (In the Loop). Health Matters is written by TIME's health desk. #### How do I sign up for a TIME newsletter? Go to time.com/newsletters, choose the newsletters you want and enter your email address. There is no cost and no subscription requirement. ### Sources * TIME Newsletters: [time.com/newsletters](/c/time-nl-network-2026q3/newsletters?i=f88cbf58-9300-4fb7-80e5-b24ebaf4d564&cr=time-nl-network-2026q3-v1) ## Video: Tracking the Vaccine: From Freezer to Front Line [Watch (HLS stream): Tracking the Vaccine: From Freezer to Front Line](https://cdn.jwplayer.com/manifests/0dwzz5K2.m3u8) (4:28)  _Published 2021-01-20. TIME followed the vaccination process from a Walgreens freezer to a long-term care facility to see what the roll out can look like._  by [Alice Park](https://time.com/author/alice-park/)  ## Alice Park Senior Correspondent Mar 9, 2021 4:17 PM UTC  by [Alice Park](https://time.com/author/alice-park/)  ## Alice Park Senior Correspondent Mar 9, 2021 4:17 PM UTC The U.S. now has [three safe and effective COVID-19 vaccines](https://time.com/5942737/johnson-and-johnson-covid-19-vaccine-fda-review/) being shipped around the country and making it into people’s arms. All meet the U.S. Food and Drug Administration’s threshold for protecting people from COVID-19 disease. Yet two of them are about 95% efficacious, while another is 66% efficacious, which may make it tempting to rank them, and assume that people receiving the 66% efficacious shot are somehow less protected against COVID-19. That’s not the case, however, since it’s not really possible to compare the vaccines to each other. In the table below, we’ve laid out what goes into that so-called vaccine efficacy number, and how you should evaluate the currently authorized vaccines: To start, there’s a difference between efficacy and effectiveness. “Efficacy” refers to the results for how well a drug or vaccine works based on testing, while “effectiveness” refers to how well these products work in the real world, in a much larger group of people. Most people, however, use them interchangeably. Next, it’s important to understand what these companies were actually measuring to come up with their efficacy numbers. In the case of the COVID-19 vaccines, the researchers were measuring how well their vaccines protected against symptoms of COVID-19\. So their vaccine efficacy numbers refer to how well they lowered people’s chance of getting sick with COVID-19\. Pfizer-BioNTech’s vaccine is 95% efficacious, meaning that for vaccinated people, it was 95% efficacious in protecting people from getting COVID-19 symptoms. It does not mean that 95% of people vaccinated won’t get COVID-19 and 5% will. Similarly, Moderna’s vaccine is 94% efficacious, so it was 94% efficacious in protecting people from COVID-19, and Johnson and Johnson’s vaccine is 66% efficacious in doing the same. But that doesn’t tell the whole story, for a few reasons. First, the vaccines **work in different ways**. Pfizer-BioNTech and Moderna developed their vaccines using mRNA technology, which involves taking the genetic code for the spike protein of the SARS-CoV-2 virus and encasing it in a fat-based particle that is injected into the body. Once inside cells, those viral genes instruct immune cells to produce copies of the protein, which in turn switches the immune system into action, churning out cells like antibodies, among other activities. If the vaccinated person then gets infected with the actual virus, the body is ready to quickly produce those same antibodies that can stick to the virus and block it from infecting cells. Johnson & Johnson-Janssen’s vaccine uses a different strategy—a weakened cold virus that is reprogrammed to include the code for the spike protein. Once inside the body, the viral genes trigger a similar dedicated response against the virus. Because the vaccines use different ways to alert the immune system, the differing technologies could lead to varying degrees of efficacy. Second, each vaccine has **different dosing regimens**. Pfizer-BioNTech’s and Moderna’s shots require two doses—in Pfizer-BioNTech’s case, the two shots are 21 days apart, and in Moderna’s case, they are 28 days apart. Janssen’s vaccine is a single shot. Pfizer-BioNTech and Moderna say their shots can stimulate the immune system after a single dose, but the second dose is needed to trigger the maximum response. Janssen’s scientists are also testing a booster dose of their vaccine to see if it too might amplify the immune response. Third, the vaccine companies **started recording COVID-19 symptoms at different times** after vaccination to see how well their shots could prevent disease. In their respective late-stage studies, Pfizer-BioNTech started recording symptoms seven days after people received the second shot of its vaccine or placebo; Moderna started 14 days after the second dose; and Janssen recorded results from both 14 days and 28 days after its single dose. Fourth, the vaccines were **tested at different times**. That’s important because of the genetic variants of the virus—some of which are more infectious than the original—that have emerged in recent months, after some companies had already completed initial testing of their vaccines. Pfizer-BioNTech and Moderna both tested their shots through most of 2020, when SARS-CoV-2 had not mutated as much, so most of the study participants who were infected, were infected by the same viral strain. Janssen, however, started its large phase 3 trial in September, and included people in the U.K., South Africa and Brazil, the three countries where new, mutated variants of the virus started to spread quickly. Indeed, many of the people in Janssen’s trial in those countries were infected with the new variants. From a scientific point of view, that means Janssen’s study provided important clues about how well its vaccine could confront the growing threat of new variants of the virus. That could also explain why the Janssen vaccine’s efficacy is lower than those of the Pfizer-BioNTech and Moderna shots. In fact, studies have since shown that among people vaccinated with the Pfizer-BioNTech and Moderna vaccines, the level of antibodies against the South African variant in particular are up to six-fold lower compared to levels against the non mutated virus. So for all of these reasons, comparing the three vaccines is a bit like comparing apples to oranges. What’s important is that all fight COVID-19 according to the FDA’s standard of efficacy, which is that vaccines should be at least 50% efficacious in protecting people from disease. And all are extremely effective in protecting people from getting severely ill with or dying from COVID-19, which, ultimately, is what we’d want any vaccine to do. ## Transcript But I am very excited that you finally come up with a vaccine. I feel the weight of it that this is going to do some good for us. And you know that I'm ready for it to start happening. You know, waiting to be in line to get my shot to. Just all the way to the Yankees or. Don't sign for Colbert. So they don't say. I actually. The biggest challenge has been temperature requirements, because that has to be kept at ultracold temperature of negative seven degrees Celsius. Or if we are transporting in a refrigeration, we have a lot more monitoring for that because it's only good for so many hours if the temperature excursion happens. And then there is a lot of responsibility in terms of liability. This vaccine has been very popular, so we have security protocols. We are putting SEALs when they're transporting. We have cameras installed specifically for this over and. Yeah. And be sorry. All right. Keep your arm relaxed. Oh, just the needle all done. You're not even bleeding. So my grandmother actually just passed away, I mean, less than two months ago from it. So to be out here protecting other people's grandparents is really touching me personally. Like, I really appreciate the opportunity and just so happy to be a part of it. The staff members here, we have about 240 that we're doing. We can get through usually with this many immunizations, 40 or 50 an hour at this facility specifically, we have over 100 residents that are all room to room based. So that takes a little more time. And then have you ever had a reaction after receiving a vaccine in the past? I can see how grateful they are. And I'm just grateful and honored to be able to give them the vaccine for me to be able to do it directly. You know, the last patient I just did, she's like, I'm waiting for the vaccine. And I was like, I'm here with the vaccine. And she's like, You're here with the vaccine. So I'm part of the bigger movement of vaccinating basically America. And that's it. Well, that's the easiest one I ever had. I'm glad with hay fever, I was you know, they can't come and visit me and I can't go visit them. But it's. Oh, gosh, it makes me mad anyway. It really is hard. And it's been harder for a lot of other people who have lost folks. And so I haven't had that problem, but it's awful. So I will mask myself any time to prevent that from happening. When I was a kid, everybody knew people who had somebody in their family that had polio. Any vaccine that prevents unnecessary pain and suffering is a good thing to have. All right. I'm just going to sanitize your arm real quick. I am happy that my son sometimes he talks to me on Facebook on face time. This time. And my daughter calls me every night. I know I can touch them and see them, but I just think the time will come. I hope. I hope I'm still alive. And make sure you're safe. ```json [{"@context":"https://schema.org","@type":"NewsArticle","@id":"https://time.com/5945177/covid-19-vaccine-effectiveness/","mainEntityOfPage":{"@type":"WebPage","@id":"https://time.com/5945177/covid-19-vaccine-effectiveness/"},"headline":"Breaking Down What COVID-19 Vaccine Effectiveness Means","datePublished":"2021-03-09T16:17:09.000Z","dateModified":"2026-10-14T09:10:30.305Z","description":"How effective are the COVID-19 vaccines? Is one vaccine more effective than the others? 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