[Corrected] Rhode Island September 2021 Data Reveal “Natural Immunity” Afforded ~90% Greater Protection, Relative to Full Covid-19 Vaccination, Against Covid-19 Infection, Hospitalization, and Death

Corrected data [see full data and email correspondence links at bottom of this posting] on September 2021 hospitalizations and deaths were just released Tuesday, October 19, 2021 from The Rhode Island Department of Health (RIDOH) to Rhode Island state representative Mike Chippendale.

These RIDOH data for September, 2021 reveal that 3177 covid-19 infections were recorded in those fully vaccinated, versus 6084 among those who were not fully vaccinated (note: RIDOH pools the unvaccinated and partially vaccinated, and dubs them all “unvaccinated”), and 292 in those with a history of prior SARS-CoV-2 infection, a surrogate for “natural immunity.” 136 covid-19 hospitalizations were tallied among those who were fully vaccinated, compared to 396 in the not fully vaccinated, and 15 in those previously SARS-CoV-2 infected. 27 deaths were recorded in those fully vaccinated, versus 38 among those not fully vaccinated, and 2 in those with a history of prior SARS-CoV-2 infection.

Calculating simple, unadjusted population-based rates (per 100,000) puts these September 2021 Rhode Island covid-19 mortality and hospitalization data in clearer, more meaningful perspective. To do so, requires estimates of the number of Rhode Islanders fully vaccinated, or not fully vaccinated, and the number with a history of prior infection. I chose the September 15, 2021 midpoint of the month to estimate the both the numbers fully vaccinated, or with a history of prior covid-19 infection.

According to the public RIDOH database, by September, 15, 2021, ~684,000 Rhode Islanders were fully vaccinated. Rhode Island’s 2021 estimated population is 1.1 million. Subtracting the ~684,000 fully vaccinated from the total Rhoode Island population yields ~ 416,000 not fully vaccinated. Lastly, per the website “Covidestim.org,” a project supported by the Centers for Disease Control and Prevention, and directed by epidemiologists from Yale, Harvard, and Stanford universities, 58% of Rhode Islanders, or ~638,000, had been covid-19 infected at some point during the pandemic, as of 9/15/21.

Applying these estimates yields the following rates, for covid-19 infections, hospitalizations, and deaths:


—3177 fully vaccinated “breakthrough” infections/684,000 fully vaccinated= 464.5/100,000

—6084 not fully vaccinated infections/416,000 not fully vaccinated= 1462.5/100,000

—292 infections among those with prior infection history /638,000 with prior infection= 45.8/100,000


—136 fully vaccinated breakthrough hospitalizations/684,000 fully vaccinated= 19.9/100,000

—396 not fully vaccinated hospitalizations/416,000 not fully vaccinated= 95.2/100,000

—15 hospitalizations in those with prior infection history/638,000 with prior infection= 2.3/100,000


—27 breakthrough deaths/684,000 fully vaccinated= 3.9/100,000

—38 not fully vaccinated deaths/416,000 not fully vaccinated= 9.1/100,000

—2 deaths in those with prior infection history/638,000 with prior infection= 0.3/100,000

Crude relative risk estimates for covid-19 infection, hospitalization, and mortality, comparing prior infection history, to full vaccination, were calculated from the data above, using unadjusted odds ratios. Having a prior infection, versus being fully vaccinated, conferred a 90.2% reduction in the occurrence of covid-19 infection [odds ratio 0.098; 95% confidence interval= 0.087-0.116], an 88.2% % reduction in the occurrence of covid-19 hospitalization [odds ratio 0.118; 95% confidence interval= 0.069-0.202], and a 92.1% reduction in the occurrence of covid-19 death [odds ratio 0.079; 95% confidence interval= 0.019-0.334]

Link to excel data spreadsheet for September 2021: Corrected RIDOH Sept 21 Infs_Hosps_Mort

Link to RIDOH email correspondence explaining their corrected data transmission: RIDOH_Chippendale emails on Sept 21 data

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