Doctors from the University of Ferrara, University of Bologna, and the Local Health Unit of Pescara studied the entire population of the Abruzzo Region in Italy to know the rate of COVID-19 (CV19) reinfection.
They defined reinfection as the presence of two positive PCR samples ≥45 days apart with ≥ 1 negative PCR test in between. The negative PCR is essential to ensure that the first infection has entirely resolved.
Subjects were classified as “vaccinated” if they received ≥1 dose of Pfizer BNT162b2, AstraZeneca ChAdOx1 nCoV-19, Moderna mRNA-1273, or Johnson and Johnson JNJ-78436735, ≥14 days before the reinfection.
The analysis included a total of 84,907 subjects with a primary infection. Here are the results (emphasis added)
In this retrospective cohort analysis of the entire population of an Italian Region, we followed 1,293,941 subjects from the beginning of the pandemic to the current scenario of Omicron predominance (up to mid-January 2022).
After an average of 334 days, we recorded 260 reinfections among 84,907 previously infected subjects (overall rate: 0.31%), two hospitalizations (2.4 x100,000), and one death.
Importantly, the incidence of reinfection did not vary substantially over time: after 18-22 months from the primary infection, the reinfection rate was still 0.32%, suggesting that protection conferred by natural immunity may last beyond 12 months. The risk of reinfection was significantly higher among the unvaccinated subjects, and during the Omicron wave.
The one person who died is a 73-year old female with significant cardiovascular disease and diabetes. There was no mention of her vaccination status, but I speculate that she is probably vaccinated, considering age and comorbidities.
Who gets reinfected?
The reinfection rate was significantly higher among females, younger subjects, and
unvaccinated individuals (0.50% vs. 0.25% among those who received ≥2 vaccine doses).
What variant caused the most reinfections?
There is a markedly higher rate of reinfections during the first 17 days of the Omicron wave (n=144/84,791; 8.5 per day) than during the 317 days of the pre-Omicron period (n=116/84,907; 0.4 per day). This means that previous CV19 infections conferred protective immunity against the Alpha, Beta, Epsilon, Gamma, and Delta variant waves.
The graph below shows the COVID-19 cases in Spain from December 2020 to January 2022, by variant.
COVID-19 shot effectiveness against variants
The study also concluded that more than two vaccinations do not protect against getting infected with the Omicron variant.
When the analysis was stratified by circulating variant, the effectiveness of ≥2 vaccine doses was substantially higher in pre-Omicron (adjusted hazard ratio – HR vs. unvaccinated: 0.20; 95% Confidence Interval: 0.12-0.33) than Omicron wave (HR: 0.57; 0.36-0.90)
Like in other countries, the Omicron variant did not cause higher mortality.
Although the marked increase of the reinfection rates during the Omicron wave is concerning, the risk of a secondary severe disease or death remained close to zero.
The study concludes with a recommendation to reexamine booster shot policies.
Therefore, despite the vaccines were able to significantly reduce the likelihood of reinfection in both pre-Omicron and Omicron waves, the risk-benefit profile of multiple vaccine doses for this population should be carefully evaluated
- USA study: Adults and children with the Omicron variant have milder COVID-19
- COVID-19 in children under five years old with Omicron is mild compared to the Delta variant
- Omicron infections elicit neutralizing antibodies against variants of concern.
- Multinational study shows why the Omicron variant has low fatality and high infectivity.
- Higher number of COVID-19 cases but no change in death rates. The South African omicron experience
My thoughts
This study is consistent with what we know about natural immunity. Naturally acquired antibodies from COVID-19 last up to 20 months.
Among 10,000 people infected with COVID-19 in the Abruzzo region, only 32 will get reinfected. The study shows that the risk of reinfection is greater among the unvaccinated than the vaccinated. But we have to look at their definition of vaccinated, which is “≥ one dose of any COVID shots ≥ 14 days before the reinfection.”
That means those reinfected with COVID-19 who had their first COVID vaccine shots within the past 14 days ago are still counted among the “unvaccinated.” That definition matters because data from Alberta, Canada, showed that COVID-19 reinfections usually occur two weeks after getting the COVID jabs. The methylation of the nucleotides in the mRNA shots lowers innate immunity and makes a person prone to infections. You can read about that in Defective immunity and COVID-19 antibody-dependent enhancement in Alberta, Canada.
Thus, the reinfection rate among the unvaccinated is most likely lower than reported in this study. Overall, it is a good study and adds more evidence to the power of natural immunity.
Risk of SARS-CoV-2 reinfection 18 months after primary infection: population-level observational study just came out yesterday and is a preprint and not yet peer-reviewed. It is available at medRxiv.
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Related:
- Asymptomatic or mild symptomatic COVID-19 elicits effective and long-lasting antibody responses in children and adolescents.
- T cells from prior coronavirus protect, and nucleocapsid-directed COVID-19 shots may work better.
- T cells from previous infections and shots are protective against the Omicron variant.
- Omicron infections elicit neutralizing antibodies against variants of concern.
- High Anti-SARS-CoV-2 Antibodies Among the Unvaccinated in Bangui, Central African Republic
- COVID Vaccines are Non-Sterilizing and Can Lead to More Infectious Variants
- Study Shows Decreased Antibody Response to Breakthrough Infections
- Pre-Existing T-Cells Stop COVID-19 Before it Starts
- Breakthrough Cases Spread COVID-19 as Easily as the Unvaccinated
- Harvard: Immunity from mild COVID-19 infection much better than vaccination
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