Comparing SARS-CoV-2 natural immunity to vaccine-induced immunity: reinfections versus breakthrough infections

I am sure many of you have heard about the study out of Israel that has declared, based on its finding, the body’s natural immunity has proven more effective on the variants, specifically the recent Delta variant. The study is a pretty dry read, so as a writing exercise as I did with another study over 42 pages, I will attempt to break this one down into plain language so that it too can be better understood. 

Overall, 673,676 people 16 years and older were eligible for the study group. 62,883 fully vaccinated were eligible, and finally, 42,099 people were suitable for the study group of unvaccinated previously infected. 

Another thing to keep in mind this study focused primarily on the Delta variant that was dominant in Israel at the time. 

I believe what prompted this study was the growing reports of the vaccine’s effectiveness. To best describe how this study was performed without using their words will take a bit of work since they describe it as the following: “The study was done retrospective observational study comparing three groups where three multivariate logistic regression models were applied.“ and it only gets more complicated from there.

The study was comprised of three groups, all 16 years of age and older:

1) Those who had previously contractive COVID and recovered.

2) Those not exposed to COVID but had two doses of the Pfizer vaccine

3) Those who were exposed to COVID and had only one dose of the Pfizer Vaccine. 

The study then looked for four things:

1) Infection – How easily did the subjects become infected

2) The severity of the symptoms

3) COVID related hospitalizations

4) Deaths

The study also involved a follow-up period from June 1 to August 14, 2021, when the Delta variant was dominant in Israel. Each group was compared by age, sex and time of the first event. 


Group #2 – The group with two doses of the vaccine showed a 13 fold increased risk of infection for the Delta variant compared to Group #1, those previously infected. The confidence level of the results was 95%. Confidence level or CI is used to qualify study results. The increased risk for symptoms was significant, and this came with a P factor of (P<0.001), a scientific term that suggests probability. Scientists like to determine the potential of their findings would have happened anyway regardless of the control group. A P factor of (P<0.05) is considered good and supports the results. A P-factor of (P<0.001) is extremely good and can be accepted to be factually accurate. 

Group #3 – Stong evidence of waning natural immunity demonstrated a 5.96-fold increased risk of infection and a seven-fold increase to symptoms with a 95% Confidence Level compared to Group #1, those previously infected. This group also showed a rise in hospitalizations compared to group #1. 

Conclusions: This study demonstrated that natural immunity confers longer lasting and more robust protection against infection, symptomatic disease and hospitalization caused by the Delta variant than those who had either one or two doses of the vaccine. 

This analysis demonstrated that natural immunity affords longer-lasting and stronger protection against infection, symptomatic disease and hospitalization due to the Delta variant. Notably, individuals who were previously infected with COVID and given a single dose of Pfizer vaccine gained additional protection against the Delta variant. The long-term protection provided by a third dose, recently administered in Israel, is still unknown.

Some general observations mentioned in the study were long-term effectiveness across different variants are still unknown. However, reports of decreasing immunity are beginning to surface, not merely in terms of antibody dynamics over time in real-world settings.

Natural immunity showed no signs of waning immunity during the tests conducted for at least seven months for those aged 65 or older.

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