Data Snapshot: How many Americans appear "immune naive" to Covid-19?
Between vaccines and infections, the immune systems of most US residents have seen this virus. What does that mean?
Major predictors of how well a body will tolerate Covid-19: age, baseline health, and vaccination status.
Another predictor that often gets overlooked? Infection history.
People who have survived a previous Covid-19 illness are far less likely to be hospitalized or die upon repeat infection. While repeat infections are certainly worse than not having them, pulling through a prior Covid-19 illness is meaningfully prognostic for future infection outcomes.
Keep in mind that immunity to Covid-19 is not all-or-none. The reality is complex. But for most people with intact immune systems, memory to the infection or to vaccination provides long lasting protection against Covid-19 death or pneumonia requiring mechanical ventilation/intubation. (For people with complicated medical histories, staying up-to-date matters.)
We wanted to know how many people are walking around who have never been exposed to Covid-19 in any form (or appear that way). That is, how many US residents have Covid-naive immune systems—or have such little remaining immunity that they don’t have enough antibodies to be detectable in blood samples. (The percent of people in a population who have detectable antibody levels is called “seroprevalence.”)
Most people appear to have at least some detectable Covid-19 antibodies.
The data indicate that during the 3rd quarter of 2022 (latest data), around 96% of the population had at least some antibodies in their system. (Caveat: the numbers come from a CDC project tracking around 143,000 blood donors over time. This may be a group that is somewhat more likely to have had Covid exposures than the general mobile population, but the results are probably reasonably indicative).
Below, we’ve broken things down by demographic. Notice the group with the lowest antibody seroprevalence is persons ages 65 and older. This surprised me. At first.
Like I did, you might be wondering why US residents ages ≥65 years—the group with the highest vaccination rates—has the fewest people with detectable antibodies? The answer is two-fold. First, this group has clearly been the most careful during the last 3 years. Only 47% of US residents ages ≥65 have had a past infection. Second, waning of immunity (whether from infection or vaccination) occurs more rapidly in older populations.
Here are the three US states/jurisdictions with the highest Covid-19 seroprevalence among residents ages ≥65, as of late 2022 (excluding Alaska, Florida, and Hawaii, due to inadequate reporting).
Washington, DC (100%)
Delaware (100%)
Iowa (99.2%)
(Source: CDC.)
Here are the three US states/jurisdictions with the lowest Covid-19 seroprevalence among residents ages ≥65, as of late 2022 (again excluding Alaska, Florida, and Hawaii, due to inadequate reporting).
Nevada (93.6%)
Maryland (93.1%)
Arizona (92.7%)
(Source: CDC.)
Keep in mind, these seroprevalence figures are yes/no results. It may be that a large number of people in these areas do not have adequate antibodies to prevent infections but do have enough (i.e., any) so that once infected, their immune system’s memory banks get roused and activated in time to defend from the viruses’ worst outcomes.
Below, you can find two interactive dashboards with state-by-state heat maps showing the relative seroprevalence due to infections, vaccinations (or both); one map shows data for all ages, while the other shows data for residents ages ≥65 years only. In addition, there is a top and bottom 10 list of seroprevalence by state for the ages ≥65 demographic. These resources are available for paid subscribers.
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