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Reinfection Data Update

By October 20, 2022Commentary

Dave Dixon just does amazing work, and it dogged in his pursuit of better data from DOH.  He has succeeded in getting some new files and including some better data on reinfections, which is very important.  We aren’t there yet, but ideally we would get comprehensive data on reinfections and breakthroughs, since there is overlap, and that kind of data would allow us to have a much better assessment of the relative protection afforded by prior infection and/or vax.  As you can see, detected reinfections are rising as a proportion of all detected infections, which reflects the reality that everyone is going to get infected multiple times.  Who knows what the real number of infections or reinfections is.

Dave’s notes:

  1. We last published charts displaying Minnesota Covid reinfection case data on 8/04/2022 here: . The Minnesota Department of Health (MDH) stopped publishing data on Covid reinfection cases, hospitalizations, and deaths on 6/30/3033. Since then we have filed several requests for reinfection data under the Minnesota Government Data Practices Act. MDH most recently fulfilled our request for reinfection data on 10/14/2022. The data MDH provided is a list of all reinfection cases by specimen collection date, along with the age of the individual, a Yes/No flag for whether or not the individual was hospitalized, and a Yes/No flag for whether or not the individual died. However, although we received the data file on 10/14/2022, the file name indicates that the file was generated on 9/23/2022, and the newest reinfection case in the file occurred on 9/21/2022.  We previously had an agreement with MDH to be given breakthrough and reinfection case data on a monthly basis, and we will file another request in an attempt to get refreshed data on or around 10/21/2022.
  2. It is important to note that MDH did not provide several other pieces of information that we have requested. We have asked repeatedly over the course of the pandemic for vaccination information for individuals who were reinfected, but MDH has said that it is not possible for them to provide this data. This means that we have no knowledge of how many of these reinfection cases were also vaccinated or boosted. We have also asked for the date of initial infection along with the date of the reinfection, but this has also not been provided.
  3. It is also important to note that only reinfections that were detected via an official Covid test performed by a clinic or hospital that communicates results to MDH is included in this data set. Home Covid test results are not included. Also, anyone who had mild enough symptoms that they never sought testing or treatment is not included in this data set. It is likely a large number of people fall in this category, which will influence the results shown on these charts. However, it is hoped that the trends over time may still indicate how the pandemic is proceeding, even if the absolute values of the data is unknown.
  4. Fig. 1 displays the total daily Covid cases in Minnesota and the total daily Covid reinfection cases. The cases per day by date are found in a data named “c7day.csv”, available on the MDH Case and Variant subpage, in the notes under the graphic “Cases Over Time (7-Day Moving Average)”. The reinfection cases per day are found in the reinfection data provided under the Data Practices Act request, as stated in Note 1 above.  Both of these curves are plotted as 7 day running averages. In order to minimize incomplete reporting, and because the reinfection data ends on 9/21/2022, this chart is stopped at 9/13/2022.
  5. Fig. 2 displays the proportion of daily total Covid cases that are reinfections, taking the ratio of the 7 day running averages. The proportion of reinfection cases surged in late December 2021 with the arrival of the Omicron variant, and has recently risen to a peak of 21.1% on 9/13/2022. It is logical that the proportion of reinfections should rise over time, since the population of previously infected people continues to increase. The waning of immunity over time, both natural and due to vaccination, will also tend to be more of a factor as time goes by.
  6. Fig. 3 shows the proportion of Covid cases each week in each age group that are categorized as reinfections. The 65+ had the highest proportion of reinfections throughout the early part of the pandemic, peaking at approximately 17.5% in the summer of 2021 when the overall number of cases was very low.
  7. Fig. 4 shows the same proportion of Covid cases each week as in Fig. 3, but starting on 12/05/2021 in order to see how the Omicron variant has behaved in more recent months. The differing levels of vaccination in each subgroup is likely to be affecting the proportions of reinfections. The size of the population in each age group that has a prior infection, and thus available for possible reinfection, is dependent on the rates of infection. For example, looking at the rates of infection per 100k here we can see that during the large spikes in cases in late 2020 and early 2022 that the 18-49 age group has significantly higher infection rates per 100k than the other age groups, which may contribute to the higher reinfection proportions for this age group throughout most of 2022.
  8. Fig. 5 and Fig. 6 show the proportion of weekly reinfection cases who went on to be hospitalized. Early in the pandemic there are very few reinfections, leading to instances where the hospitalization rate is 100%. For example, the most recent time that 100% of the reinfection cases were hospitalized was for the week of 6/6/2021 for the 0-4 age group, where there was only one reinfection case. More recently the 65+ age group peaks at 33.5 % for the week 3/13/2022. Note that, as seen in Fig. 1, around this time Covid cases and reinfections were at a low point. Note also that there have been recent reports published in the StarTribune here that between 50% and 75% of Covid hospitalizations were actually admitted for a non-Covid reason. Undoubtedly many of these incidental Covid hospitalizations will also be reinfections.
  9. Fig. 7 and Fig. 8 show the proportion of weekly reinfection cases who went on to die. Looking at the entire pandemic in Fig. 7, there are quite high rates of death for reinfection cases early in the pandemic where there were relatively few reinfections. When there are few reinfections it would only take a handful of missed reinfection cases to dramatically drop the reinfection death rate, especially in early 2020 when testing was still somewhat limited. For this reason Fig. 8, showing data since 12/05/2021 is probably more representative. The 65+ age group peaks on 3/13/2022 at 6.3%, the same week that the hospitalization rate peaked for this age group. Not surprisingly, the 65+ age group account for the vast majority of the reinfection deaths, along with a relatively small number of individuals in the 50-64 age group.

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