Maybe it is lower because it is the second infection some had.
Quote:
“National data show an exponential increase in both new infections and test positivity rates during the first three weeks of this wave, indicating a highly transmissible variant with rapid community spread of infection.”
[1] https://www.nytimes.com/2021/11/28/world/africa/south-africa...
https://jim.bmj.com/content/69/6/1253
It's a small sample, but it was done on data available in 2020, which was before vaccines were available.
Small sample size, but even similar result is somewhat surprising -- I would've thought the 2nd infection would be weaker.
It's not that much larger -- I guess reinfections are hard to find -- but surprisingly this found that ICU admission was higher for reinfections.