Sterilizing Immunity and COVID-19 Vaccines

Source: Verywell.

I never heard the term sterilizing immunity until just the other day, but the concept was deeply embedded in my own assumptions. I assumed that all immunity is “sterilizing,” meaning that disease and infection are both prevented. It turns out that immunity can also be “non-sterilizing,” meaning that while disease is prevented infection is not.

I find the distinction useful for making sense of media reports on Covid-19 vaccines. For example, when a journalist talks about the “efficacy” of a vaccine you can usually interpret that as referring to its sterilizing effect. In fact, effective immunity — also called practical immunity — is synonymous with non-sterilizing immunity.

The Covid-19 vaccines confer non-sterilizing immunity. That’s much simpler to understand than the idea that no vaccine is perfect.

5 thoughts on “Sterilizing Immunity and COVID-19 Vaccines

  1. This is the first I have heard the term ‘sterilizing immunity’ and I find it conceptually an impossibility.

    The HPV vaccine breaks the chain of contagion not because the antibodies are special but because there is a very long time lag between infection and the ability to pass the virus on. You get infected, and get well, before you start shedding the virus from the lesions.

    It is the disease, not the antibodies or the vaccine which is different.

    Liked by 2 people

    1. RE: “You get infected, and get well, before you start shedding the virus from the lesions.”

      I’m confused. The source article suggests that HPV vaccines prevent the initial infection. Other sources (e.g., Wikipedia) say the same.


      1. I think it will depend on what they mean by ‘infection.’

        If they mean before there are clinical signs, then OK.

        But if they mean that no cells are breached, that is problematic.

        Over your lifetime, you are exposed to thousands of microbes and other antibody generating antigens. If you kept enough antibodies to block an initial infection from all of them, your blood would be a thick as honey.

        What happens instead is that when your body detects the end of an infection. it turns off production of those antibodies, and those in circulation are mostly recycled. Enough remain to be detected, but not nearly enough to instantly overwhelm an infection. But the body has cells that remember how to make those antibodies and can mass produce them very quickly if needed.


      2. RE: “But if they mean that no cells are breached, that is problematic.”

        Got it. I see what you mean when you describe “sterilizing immunity” as a conceptual impossibility.

        And yet, sterilizing society of Covid-19 is what I and many others expected the vaccines to do. It is a bit of a shock to learn that that isn’t going to happen, or hasn’t begun to happen with the current vaccines.


  2. The article was from December 24, 2020. In the last 7 1/2 months we have learned a lot more about vaccine and immunity. Still, there are a lot of questions about waning effect, booster shots, contagiousness of the vaccinated, etc.

    I think the issue revolves around the rapidity of the mRNA vaccine development in comparison to older styles of vaccines which took years to develop.

    Yet there are two conflicting worries:

    First, what are, if any, long term effects of the vaccines.

    Second, what are the long term effects of COVID itself.

    Neither one of these concerns can be solved except through either well designed experiments that “speed up” effects over time, or time itself. However, we have had almost a year of extensive testing, starting with 30,000 or more volunteers for phased testing and then hundreds of millions of inoculations here and worldwide.

    Personally, I have confidence that the vaccine benefits are far and above any risks. Or, more pertinent, the risks of not vaccinating to both the individual and the nation were pretty well established by the 600,000++ deaths, millions of hospitalizations and probably trillions of dollars in both spending and economic damage.


    Liked by 1 person

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