Last week, I wrote about a second major study finding that natural immunity protects better against infection than the Pfizer vaccine. Both this study and the earlier one were from Israel, and while there’s every reason to believe the results generalise to other populations, it’s always good to have data from multiple countries.
We now have those data in the form of a study published by the Statens Serum Institut in Denmark. I can’t say the report itself is worth reading in full, since it’s written in Danish. But I’ve posted the key figure below. It shows protection against infection for three different groups – adjusting for age, sex, comorbidities, and time of year.
The orange line corresponds to people who’ve been previously infected but not vaccinated; the yellow line to those who’ve been previously infected and vaccinated; and the green line to those who’ve been vaccinated but not previously infected.
The y-axis gives the percentage reduction in the number of infections, compared to those who haven’t been vaccinated or previously infected. For example, a value of 90% means there would be only 10 infections for every 100 in the comparison group. The x-axis gives the number of days since the relevant event.
As you can see, vaccine-induced immunity wanes rapidly, beginning a few weeks after vaccination. And at the five month mark, protection is well below 50%. Natural immunity, by contrast, is robust: a full year after infection, protection is still above 70%.
Consistent with what the two Israeli studies found, hybrid immunity – conferred by the combination of vaccination and previous infection – is slightly better than natural immunity. However, the difference is small compared to that between natural and vaccine-induced immunity.
Evidence for the superiority of natural immunity is now robust. So while those who’ve already had Covid should be perfectly free to get vaccinated, there’s no obvious need for them to do so. The tricky part may be getting this message through to politicians.