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.