This study investigates the diminishing levels of protection against SARS-CoV-2 infection among individuals who have fully recovered and BNT162b2 vaccinees who have not been infected.

Researchers recently examined the features of natural and hybrid immunity to infections caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Their findings were reported in a paper that was recently distributed by The New England Journal of Medicine.

Infections with the coronavirus responsible for illness 2019 (COVID-19) are known to be capable of inducing natural immunity against reinfection. Several investigations have revealed that the immunity against SARS-CoV-2 that was induced by vaccination is beginning to wane. On the other hand, further study is required in order to have a complete understanding of the many properties of natural and hybrid immunity.

Concerning the Research

In the current study, researchers analyzed the frequency of confirmed SARS-CoV-2 infections across cohorts consisting of previously SARS-CoV-2-infected and unvaccinated people, BNT162b2-vaccinated persons with a history of infection, and vaccinated individuals with no history of COVID-19 infection.

During the course of the research project, which lasted from the first of August 2021 to the thirty-first of September 2021, the team extracted data from the national database maintained by the Israeli Ministry of Health. The database included demographic information such as age, gender, area of residence, and population sector associated with Israeli residents who were vaccinated with a COVID-19 vaccine, had previously been tested for COVID-19, or had a history of COVID-19 infection. Additionally, the database included information regarding whether or not the individual had a history of COVID-19 infection. Study participants had to be SARS-CoV-2 positive before July 1, 2021, or they had to have been vaccinated with a minimum of two doses of the BNT162b2 vaccine at least seven days before the study period ended. The data that was obtained was used to study confirmed cases of SARS-CoV-2 infections in individuals aged 16 years and older.

For the purposes of this investigation, the researchers considered a positive polymerase chain reaction (PCR) test to indicate reinfection with SARS-CoV-2 in individuals who had previously tested positive for SARS-CoV-2 at least 90 days before the study. The severity of COVID-19 was determined by the patient’s resting respiratory rate, which had to be more than 30 breaths per minute, and their oxygen saturation had to be lower than 94%.

The researchers did a comparison of the number of confirmed COVID-19 infections that occurred throughout the course of the trial across different patient groups that were defined according to their history of immunity-conferring events. Individuals who had a history of proven COVID-19 infection at least ninety days previous to the beginning of the trial were included in the recovered and unvaccinated group.

One cohort consisted of COVID-19-recovered individuals who were vaccinated with only one vaccine dose after a SARS-CoV-2 infection 90 days prior to the study. The other hybrid cohort included groups of participants who had natural immunity as well as vaccine-induced immunity. The research team also included two-hybrid cohorts. People who had no previous history of SARS-CoV-2 infection were included in a second cohort. They were given two doses of the vaccine, with the second dosage being administered seven days before the research began. The third and final group consisted of people who had received all three doses of the vaccine at least a month before the start of the research and who had no previous history of infection with COVID-19.


Over 5.7 million people were divided up into several research cohorts for the purpose of this study. The researchers found that the gender distribution was consistent across all of the study cohorts, despite the fact that there were notable changes in the distribution of the other factors. Adults aged 60 and older accounted for 53.4% of the person-days contributed to the three vaccine doses group, 8.3% of the person-days contributed to the COVID-19 recovered and unvaccinated group, 13.8 % of the person-days contributed to the recovered with one vaccine dose group, and 12.6 % of the person-days contributed to the two vaccine doses group.

The findings demonstrated that each of the study cohorts saw a gradual decrease in their level of protection in addition to a diminishing immune response during the course of the research. Within the recovered and unvaccinated sample, the adjusted rate of confirmed COVID-19 infections was 10.5 per 100,000 person-days at-risk four to six months after the infection diagnosis. This escalated to 30.2 per 100,000 person-days at risk 12 months or more after the first infection. The incidence of confirmed infection was 21.1 percent among people in the two-dose group who had been vaccinated two months before to the trial. This rate climbed to 88.9 percent among those who had been immunized six to eight months prior to the study. The rates were 3.7 and 11.6 four to six and 12 months and more post-vaccination, respectively, among the recovered cohort that had only had a single dose of vaccine.

The adjusted rates of confirmed COVID-19 infection were comparable in the subcohorts, including the recovered, unvaccinated persons, to those of the individuals who were vaccinated with one dose after COVID-19 recovery and those who were vaccinated after COVID-19 recovery when the time duration since the most recent vaccination or infection was the same across the cohorts. This was the case when the time duration since the most recent vaccination or infection was the same across the cohorts. These rates were a considerable amount lower than those that the two-dose group demonstrated four to six months and six to eight months after receiving the COVID-19 immunization. The protection that was conferred by the vaccination after two doses were, however, fully restored when the third dosage was administered.


The results of the research indicated that the protection afforded by COVID-19 vaccinations gradually eroded over time in both those who had previously been infected with COVID-19 and those who had been vaccinated against the virus. Following the delivery of a booster vaccination dose, this drop in protection was brought back to its previous level. The researchers that carried out this study are of the opinion that knowing the rates of decreasing protection following vaccination or infection is an essential component in the process of formulating policy about vaccines.

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