That paper in The Lancet is a meta-analysis – a systematic review of multiple other already published clinical studies & review articles about immunity to COVID-19 acquired from previous infection. Meta-analyses or meta-reviews aren't new data. But they’re meant as a broad comparison of the results of many other studies. Even if those various studies can’t be directly compared because of different specific conditions (such as different patient populations or different strains of virus), meta-analyses can be useful as an overview of the initial years of COVID-19 over the first 2 years since it became a widespread pandemic.
This paper estimates the reduction in risk of COVID-19 among individuals with a past SARS-CoV-2 infection in comparison to those without a previous infection. The paper’s authors ran a meta-analysis of how effective past infection was by outcome (infection, symptomatic disease, and severe disease), virus variant, and time since infection. The authors identified a total of 65 studies from 19 different countries. They used a statistical method known as Bayesian meta-regression to estimate the pooled estimates of protection. Their meta-analysis found:
- Protection from past infection and any symptomatic disease was high for reinfection with ancestral, alpha, beta, and delta variants, but was substantially lower for the omicron BA.1 variant.
- Protection from past infection against re-infection from pre-omicron variants was very high and remained high even after 40 weeks.
- Protection was substantially lower for reinfection by the omicron BA.1 variant and declined more rapidly over time than protection against previous variants.
- Protection from severe disease was high for all variants.
These results aren't too surprising considering what we've all witnessed over the last 2 years. The political right-wing as well as their sympathizers in the anti-vaccine community, who all opposed the public health emergency, jumped on this paper, saying "We told you so!" They had naively assumed that a world-wide epidemic, caused by a highly infectious new virus never previously exposed to humans, would be no big deal.
Their reaction exposes their ignorance of the dreadful history of human viral diseases. This Lancet paper is the first to document what we have learned about the immunity caused by previous infection to the disease, over the first two years of the pandemic. The authors went on to say this:
In my opinion, their last comment is far more realistic and responsible than blindly assuming that any drastic public health measures for the initial years of the viral pandemic would not be needed.