Israeli Study Compares Natural Immunity vs Vaccine-induced Immunity
To those who have recovered from COVID-19, there is good news. Well, apart from having recovered, I mean.
An Israeli observational study by Sivan Gazit et al, published on 25 August 2021, made use of their extensive data comparing natural immunity to vaccine-induced immunity. In short, vaccine-induced immunity is 13 times worse than natural immunity for infection and 27 times worse for symptomatic infection.
Three comparisons (models) were made: 1. infected individuals who have never been vaccinated versus fully vaccinated individuals with their respective time of infection or reception of second dose matched (between January 2021 and February 2021); 2. same as previous but without time matching; and 3. previously infected individuals and previously-infected-and-once-vaccinated individuals.
Since the Delta variant was the dominant variant during the study’s outcome period in Israel, this is basically about Delta infections. In regards to other variants, the study admits to being limited.
For the first model, 16,215 individuals in each group were compared.
During the follow-up period, 257 cases of SARS-CoV-2 infection were recorded, of which 238 occurred in the vaccinated group (breakthrough infections) and 19 in the previously infected group (reinfections). After adjusting for comorbidities, we found a statistically significant 13.06-fold (95% CI, 8.08 to 21.11) increased risk for breakthrough infection as opposed to reinfection (P<0.001).
As for symptomatic SARS-COV-2 infections during the follow-up period, 199 cases were recorded, 191 of which were in the vaccinated group and 8 in the previously infected group. … After adjusting for comorbidities, we found a 27.02-fold risk (95% CI, 12.7 to 57.5) for symptomatic breakthrough infection as opposed to symptomatic reinfection (P<0.001) (Table 2b).
Note the difference between “(re)infection” and “symptomatic (re)infection”.
For the second model, 46,035 individuals in each group were compared.
When comparing the vaccinated individuals to those previously infected at any time (including during 2020), we found that throughout the follow-up period, 748 cases of SARS-CoV-2 infection were recorded, 640 of which were in the vaccinated group (breakthrough infections) and 108 in the previously infected group (reinfections). After adjusting for comorbidities, a 5.96-fold increased risk (95% CI, 4.85 to 7.33) increased risk for breakthrough infection as opposed to reinfection could be observed (P<0.001) (Table 3a).
Overall, 552 symptomatic cases of SARS-CoV-2 were recorded, 484 in the vaccinated group and 68 in the previously infected group. There was a 7.13-fold (95% CI, 5.51 to 9.21) increased risk for symptomatic breakthrough infection than symptomatic reinfection (Table 3b). COVID-19 related hospitalizations occurred in 4 and 21 of the reinfection and breakthrough infection groups, respectively.
Vaccine-induced immunity is almost 6 times worse than natural immunity if timing is not matched; that is, if the natural immunity was (possibly) activated earlier than the previous model’s designated time window. This may indicate that longer-term natural immunity may not be as effective against the Delta variant but it’s still way better than vaccine-induced immunity.
For the third model, 14,029 individuals in each group were compared.
Examining previously infected individuals to those who were both previously infected and received a single dose of the vaccine, we found that the latter group had a significant 0.53-fold (95% CI, 0.3 to 0.92) (Table 4a) decreased risk for reinfection, as 20 had a positive RT-PCR test, compared to 37 in the previously infected and unvaccinated group. Symptomatic disease was present in 16 single dose vaccinees and in 23 of their unvaccinated counterparts.
In other words, natural immunity with a single vaccine dose is slightly better than mere natural immunity against the Delta variant.
For all three models, the number of (re)infections is not high given the large sample size. And, obviously, the long-term protection of natural immunity and vaccine-induced immunity is still unknown. Either way, according to this study, there is a statistically significant difference between natural immunity and vaccine-induced immunity.
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