Effectiveness of coronavirus vaccines

May 2, 2021 • 11:00 am

My doctor, Alex Lickerman, has put up post #13 in his continuing series on the medical science of coronavirus and the pandemic. This short but informative post (click on screenshot below) deals with a question we all have:

First, the effectiveness. Alex summarizes numerous studies showing how effective a vaccine is. Remember, though, what that number, expressed as a percentage, means. If a vaccine is 95% effective, it means that in a situation in which a certain percentage of people get infected, say 30%, then the chance you will get in infected is (100% – 95%) X 30%, or 1.7%.  Note that this does not mean that your chance of getting infected is 5%: it’s lower than that because not everybody gets infected when they’re not vaccinated.

Here are some effectiveness estimates taken by Alex from the literature:

Single dose Pfizer: 70%
Double dose Pfizer: 85%
Single dose Pfizer and Modern considered together, single dose: 80%
Double dose   ”            ”                   ”                 ”            double dose: 90%
The two above figures are also the same in another study not specifying vaccination

The 80%-90% holds for both symptomatic and asymptomatic infections; this means that yes, you can be an asymptomatic carrier if you have been fully vaccinated, but the chances are very small.

 Pfizer and Moderna combined (both mRNA vaccines): effectiveness: over 96%

Now remember again what these figures mean, because people get that meaning wrong all the time. Here’s one example I quote from the article:

A CNN article was skeptical of this data, arguing that “real-world studies of the Pfizer-BioNTech and Moderna vaccines show they are only 90% protective against the coronavirus, not 95% as reported in clinical trials. Translated into reality, that means for every million fully vaccinated people who fly, some 100,000 could still become infected.” Importantly, this is not what 90 percent effectiveness means! Ninety percent effectiveness means the vaccines reduce the rate of infection by 90%. To calculate a person’s absolute risk of getting infected after having been vaccinated, you have to start with the base rate of infection, which is different in different contexts. It would be true that “for every million fully vaccinated people who fly, some 100,000 could still become infected” if the base rate of infection for those million people was 100 percent. Yet the highest rate of infection we’ve seen in published contact tracing studies was around 30 percent (for spouses of infected people). This means that post-vaccination rates of COVID-19 infection in the vaccinated population are at most 90 percent less than 30 percent, or 3 percent. And that only if everyone who’s been vaccinated has an infected spouse.

In fact, the CDC reported that, as of April 20, 2021, out of 87 million fully vaccinated people there were only 7,157 breakthrough infections (0.008 percent), only 498 hospitalizations (0.0006 percent) related to COVID-19, and only 88 deaths (0.0001 percent) related to COVID-19.

Alex’s bottom line:

The mRNA vaccines are extraordinarily effective at preventing both symptomatic and asymptomatic infection and therefore at preventing transmission of SARS-CoV-2. Most importantly, if you’re fully vaccinated, your risk of dying from COVID-19 is 0.0001 percent.

What about the variants?. In answer to the question of whether the vaccines work against the variants, Alex says “yes”, at least for variants currently circulating. He adds that more data are to come.

Here’s Alex’s conclusion, which happens to echo the same conclusions reached by Bari Weiss in a piece published on her site this morning:

CONCLUSION: Given the incredible effectiveness of the vaccines at preventing both symptomatic and asymptomatic disease, and therefore disease transmission, and given that the rates of death from COVID-19 in vaccinated people is 0.0001 percent among all vaccinated people in the U.S. (an analysis that also included the J&J vaccine), if you’ve been vaccinated, we consider it reasonably safe to dine indoors, travel, and gather with even unvaccinated people. Living in the world has, of course, never been risk-free. Yet we can now say that with the advent of effective vaccines against SARS-CoV-2, the risk of living as you did before the pandemic has returned to what it was before the pandemic.

Here’s Weiss’s piece, which I think is free, though I’ve now subscribed. Click on the screenshot:

35 thoughts on “Effectiveness of coronavirus vaccines

    1. I misunderstood what that means at first. It’s only logical, though, that you will not catch covid if there is no one around to pass it on to you, so it has to depend on the number/percentage of carriers around.
      Excellent article. Thanks, Alex and Jerry.

    2. “Math is hard!” –Barbie doll. Of course, it gets a lot harder if your teacher is bad at teaching – which applies to most reporters, I’m afraid.

  1. One question I still have is whether this effectiveness number is per exposure or per person. I suppose that there is not enough data to distinguish these possibilities yet, but it might be the per exposure effectiveness. If that is the case, then it seems that even if you are vaccinated, you should not expose yourself to high-risk situations in which you might be repeatedly exposed.

  2. CNN: “Translated into reality, that means for every million fully vaccinated people who fly, some 100,000 could still become infected.”

    Getting picky, CNN’s sentence is strictly correct, since they used the would “could” not “would”. They are right that, with a 90%-effective vaccine, 10% of a cohort are still vulnerable to getting infected. Actual infection rates would of course be much lower.

    1. I’m not sure even this is quite right. If there’s a dose of virus that would infect 100% of unvaccinated people, it will infect 10% of vaccinated people. But if you keep giving people this dose over and over again over the course of a few weeks, even a vaccinated person is very likely to get infected. Of course, no one’s doing that (even ICU doctors in the covid wards weren’t getting 100% infected in the weeks when PPE was in short supply).

      I think the appropriate thing for everyone to do is to look at the local infection numbers (right now the NYTimes reports that 11 out of every 100,000 people in Austin is getting infected per day, while in Ann Arbor or New York it’s 20 out of every 100,000 people per day) and then subtract the effectiveness. So a vaccinated person in Austin has a 1.1/100,000 chance of getting infected and a vaccinated person in Ann Arbor or New York has a 2/100,000 chance of getting infected, if they’re living like the average resident.

  3. So then what would be the point behind the CDC still telling people to wear masks even if they are fully vaccinated? I’m not asking this to be contrary, but this is exactly what is being asked by a good many people. Of course many of those people are in the conservative, anti-mask, anti-vax camp but it is a valid question. If we are to trust the science and trust the vaccines, then is mask wearing necessary, or has it become health and political theater? It sounds like contradictory messages to say that people should get vaccinated, to trust the science, but then insist they also continue wearing masks. I’ve heard this discussed on several podcasts but I have yet to hear a convincing response. And for the record, I am fully vaccinated and still wear a mask.

    1. I think it is because the CDC wants to encourage public mask wearing until a larger fraction of the population is fully vaccinated. If the vaccinated can throw away their masks, then many unvaccinated will do likewise. How can one tell who is vaccinated and who is not? There are reports of the unvaccinated forging vaccination cards.

    2. IMO it it mostly theatre and PTSD-like psychology, at least on the part of vaccinated folk who continue to wear them unnecessarily. (Note: I am pro-mask, pro-vaccine, and very much not conservative.) From the CDC perspective, and they are primarily concerned with the public as a whole not the needs of individuals, the idea that “the more masks, the better” until herd immunity is achieved. They think of it in terms of “we’re all in it together”, I think. I’m sympathetic to that but fear it will backfire because for most folk, personal risk/benefit considerations take priority.

      1. That’s the only answer I’ve heard, that we can’t tell who’s vaccinated so everyone should wear masks, and of course there was the push, as the vaccines were being rolled out, to get people to wear TWO masks. That doesn’t sound like “trusting the science”. It really undermines the message, at least in my mind.

        I understand the reasoning, sort of, but the CDC should visit rural areas and notice that they’ve not being wearing masks very often anyway, at least out here in tRumpistan where I live. All I can say is that if you are not vaccinated but want to be, wear your mask and stay away from people. If you are an anti-mask, anti-vax tRump-humper, you probably won’t do what the CDC says anyway, so go ahead, do what you want, but don’t whine to me when you get sick or kill your loved ones bringing home the virus. For me, I just think it’s nice to be vaccinated and protected FROM these idiots now, if only in one small way.

        1. I can’t disagree with that. I’m lucky not to live in Trumpistan. I still worry about the “hesitant” folk. We have city-wide masking required in stores and restaurants, but many of the smaller restaurants remain open only for take-out. I recently saw one local middle-eastern place advertising that the staff was all vaccinated and offering a freebie of some sort if you showed your vaccination card. I think if we had a vaccine passport of some sort many more people would open up and there would be a very strong motivation for the hesitant folk to get their jabs.

    3. It sort of bothers me that I am supposed to wear a mask even though my doing so provides no medical benefit to anyone. Everyone should always wear masks because those in charge cannot easily tell who has been vaccinated, and who has not.
      It sort of seems like something we would make young children do, except that this is being expected of 150 million adults.
      Additionally, I am still unconvinced that any of the mask wearing has helped anyone. Nobody is wearing the sort of masks that actually provide some protection against a virus, and even if they had the right masks, they are not wearing them in a way that would do any good. Everyone keeps touching their mask, using it over and over again, and even pulling it aside to sneeze or cough.

      I mentioned here before, I used to teach bio and chemical warfare defense in the USMC. Even having the right gear, the practices that one needs to adopt require quite a bit of effort and constant attention. My wife, on the other hand, has performed a bunch of surgeries, and sees sick people every day. But she was never trained the way I was, and when we started talking about the procedures I was taught to follow, she did not have an easy time of it. Of course there are docs and lab people who work regularly with serious pathogens who certainly have the right mindset and procedures. Most people don’t. Most doctors don’t, either.

      Looking at it from that perspective, the masking thing as currently practiced seems about as effective as wearing a religious medal, or having a colored ribbon sticker on your car.
      This is not to minimize the seriousness of the pandemic.

      Beyond that, we are most of us used to expecting frank truths from people giving us medical advice. We have not been getting much of that during Covid. Some of it has been contradictory, and some policies make no logical sense. The only way that I think we can have public trust in the advice we are given is if those providing that advice are scrupulously truthful, and base their advice and particularly their restrictions, on best medical practices for each individual and for society as a whole.

      1. It did not help the situation when a little over 13 months ago the CDC was saying Americans shouldn’t wear masks, because they didn’t wear them correctly and because they were in short supply, and there was even talk about them doing harm! Then there was the “making black people wear masks is racist” and “ masks let men lear at women” claims (?!) I mean, we screwed this up so bad nobody knew who to trust, even before everybody started kowtowing to Herr tRump even when he was talking about injecting bleach and shining a UV light up your ass to cure COVID-19. Citizens need honest advice, but we got lies, misinformation, and at best, straw-grasping. Now MIT has a paper out that appears to show the 6-feet thing to be bogus too. 6 feet, 60 feet, indoors means yours all sharing the same poorly ventilated air, but outdoors, very little to worry about. Well, I guess we shall see. I do t need the experts to be perfect, I don’t need masks to be perfect, I don’t need 100% efficacy in a vaccine to take it, but I do need to be able to trust health officials and if they don’t know, I need them to say so.

        1. Despite the terrible messaging, the efforts to control the virus were not futile. Since the real world effectiveness if individual preventative measures will take time to suss out, it is helpful to look at infection rates for other viruses that are better understood. The dramatic decline in influenza cases in 2020 is good evidence that the measures taken to slow the spread of COVID-19 were effective since the means of transmission is similar to COVID-19. Eventually we will learn what specific actions were most effective and we can do a better job next time On second thought, Americans are almost guaranteed to learn the wrong lessons from any challenge but one must hope for a better outcome.

      2. just look at the 2020 seasonal flu data and you might understand why masking and good hygiene reduce viral transmission

    4. The official reason is that when a vaccinated and unvaccinated person are in a room together, the vaccinated person could become, or already be, an asymptomatic carrier. The CDC thinks the risk of serious infection in that situation is “too high” (don’t know where they set the bar). Note that if both people are vaccinated, while there is still a tiny risk of spreading the virus, the chance of either of them developing serious disease as a result is extremely tiny.

      Although darwinwins has a point too. There are definitely some people who could drive at 95 mph more safely than I can, or most people can, at 70 mph. But legally allowing them to do so would probably not be wise.

    5. The point is the enforcement. Everyone knows that it’s perfectly safe to bring a toy gun onto an airplane. But TSA has to look at millions of bags, and they can’t check each gun to see whether it’s a toy or real. So the rule is that both real guns and toy guns are banned on carry-ons. Similarly, restaurant staff can’t check each person to see whether they’re vaccinated. So the rule is that both vaccinated and unvaccinated people have to wear masks in the restaurant.

      Of course, at home, when you’re not subject to TSA or restaurant inspection, the rules are different. Your kids can have all the toy guns they want at home, and you can visit all your vaccinated friends at home without masks, but you should probably still keep real guns away from your kids, and not have un-masked home meetups between multiple un-vaccinated people.

  4. My initial plan was to get the first vaccine offered to me. Well, that hasn’t happened yet, but in the UK the Joint Committee on Vaccination and Immunisation now recommends 18-29s don’t get the Astra Zeneca vaccine due to the blood clots kerfuffle: http://www.healthscotland.com/uploads/documents/45108-Covid-19%20AstraZeneca%20vaccine%20and%20rare%20blood%20clots%20leaflet-Apr2021-English.pdf

    That leaflet says you should weigh up the risks and decide for yourself. I think, since I’m in that group and things are going pretty well here, that I’m better off waiting for another vaccine. I’m hoping for the Pfizer- I want that mRNA tech!

    1. It doesn’t quite say ‘don’t’; it says ‘not recommended at the moment’. I had my second AZ jab last Tuesday, and I’m looking forward to getting back to my life.

      The NHS is rightly being cautious, but really the risk from the AZ jab is negligible. The only reason the blood clots have even been detected is that so many people have already had the vaccine. I would say: get the first one you’re offered!

      1. Fair enough! I must admit though that part of my reasoning is just wanting to get the really cool mRNA tech jab…if they recommended getting whatever came to you first, I’d get the AZ, but since they suggest more caution in my age bracket, and since otherwise I’m probably pretty low risk for catching and really badly suffering from Covid, I think, on balance, that I can wait. Of course, if it’s the Pfizer or whatever that they offer me first, I’ll take it! But yeah, given the risks, and given that otherwise I’m not so at risk, I feel comfortable, both for myself and others, waiting.

  5. How good are the vaccines. After having the virus in January and then getting the pfizer vaccine in Mar/April I see no reason to worry about anything except getting these anti vacciners to get going.

    Also, how good is Lewis Hamilton, F1 driver currently with 7 championships. Today’s F1 in Portugal kind of tells the story. He did not win the poll. He did not lead the race in the beginning. But guess who won?

    1. He didn’t win what poll? Are you saying he wasn’t voted driver of the day? Because that sounds like a travesty if true. (I haven’t watched the race yet, but I know the result and I’ve read the reports.)

      1. As you know, they qualify on Saturday for the Sunday race. He got second and his team mate was first (poll position). So he started in second today. He was passed by Vestapin in the red bull so now third. Soon he passed him and Bottis to take first and stayed there the rest of the race essentially. Nobody had mechanical problems or anything else so he won by out driving the others.

  6. I have been in a year long battle with some other residents of my condo complex who refuse to wear masks. Now that I no longer need to wear one there is no way I will allow these fools to see me without a mask! I will continue wearing it for the foreseeable future.

    1. Are those fools anti-vaccine too? If so, then just keep a safe distance from them. Let them catch Covid if they want. If they survive they’ll be immunized.

      1. Of course it will depend which variant they catch and if they catch two of them, they can cook up a new super variant. Such helpful people.

        1. Vietnam, with a population of abt.100 million (a little less than a third that of the US), has had a TOTAL COVID death toll of 35 people. Sad the misinformation people pass along, including by the news, by not opening their mouths.
          That said, I agree. Wear a mask. There is no telling what tricks a new mutant virus will have up its sleeve, and even if the mutant pops up in Brazil, or India, or Central Europe, it won’t take long for it to be everywhere.

          1. Vietnam placed people in government run quarantine centres if someone tested positive and they had very comprehensive contact tracing. They learned a lot from SARs and I can only assume that since they are probably a more collectivist culture than the west, they were much more happy to wear masks and go to quarantine facilities at great inconvenience to themselves in order to protect others. Not so much here in the west where wearing a mask or staying out of the mall is considered a huge infringements on freedoms and be damned if an individual should sacrifice anything for the collective good!

            1. A former colleague of mine was in Vietnam with her husband when the pandemic hit. They watched in dismay as the US floundered and our death toll skyrocketed. They remain in Vietnam still, happy to have been living normal lives (visiting restaurants and bars) for all these long months.

              1. Yeah and it’s not just the US either. It’s a definite cultural thing. Imagine the reaction in any western country if their citizens were told to go to a government quarantine facility because they tested positive!

  7. Nobody mentions age in these studies. Vaccines work by stimulating the immune system to produce antibodies. But in us older folks, the reduction in thymus size means we have fewer activated T-cells and these are essential to antibody production. I’m wondering how to take that into account, now that I’m an octogenarian.

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