Researchers found post-infection protection—known widely as natural immunity—was strong and remained significant over time. The protection from reinfection against the Wuhan, Alpha, and Delta variants was 85% at 4 weeks, 78% at 40 weeks, and 55.5% at 80 weeks, respectively.
That protection dropped more quickly against the Omicron BA.1 subvariant, declining to 36% by 40 weeks, and protection against symptomatic disease also waned below 50%.
But shielding against severe disease was strong against all strains, including the BA.1 subvariant, researchers found. The naturally immune enjoyed 88.9% protection against BA.1 at 40 weeks, which was actually higher than against earlier strains.
Public health officials have repeatedly said that vaccination is better than natural immunity, or that the naturally immune should still get vaccinated despite the protection they have. Some other countries have acknowledged natural immunity by lowering the number of recommended doses for the population.
Researchers have emphasised that COVID-19 can cause problems, including death, but did not mention side effects from vaccination that can also cause long-term issues, including mortality.