(Page updated at 2021-09-07 16:57:42)
Inspired by a Washington Post article: The unseen covid-19 risk for unvaccinated people
Data are from Maryland Department of Health for vaccination (Immunet, as of 2021-09-07) and COPVID-19 cases (as of 2021-09-07).
NOTE: adjustment methods
1. Unadjusted population is estimated to be 255,441, as of July 2019.
2. * Population, adjusted using Washington Post methods: subtracting 85% of people who received one dose as of the same date. See details here
3. ** Population, adjusted based on first vaccination: subtracting 75% of people who received first does 14 days ago. Real-world effectiveness for first vaccination is 80% for PFR/MOD 14 days after the first shot. Since Harford county residents received predominantly PFR/MOD vaccine, 75% is applied to be conservative.
4. *** Population, adjusted based on full vaccination: subtracting 85% of people who received complete doses (2 PFR/MOD or 1 JSN) 14 days ago. Real-world effectiveness for full vaccination is 90% for PFR/MOD 14 days after the second shot. Since Harford county residents received predominantly PFR/MOD vaccine, 85% is applied to be conservative.
The higher vaccination coverage, the higher relative adjustment factor for unvaccinated people.
For example, for unvaccinated Asians the relative inflation in the new cases/pop is higher comapred to unvaccinated Black (hypothetically, 3 vs. 1.5, respectively). But, typically, new cases among Asians is lower than that among Black (hypothetically 2/100,000 vs. 10/100,000, respectively). So, the rate of new cases can be still lower among unvaccinated Asians than unvaccinated Black (3 x 2/100,000 = 6/100,000 vs. 1.5 x 10/100,000 = 15/100,000).
But, how do we interpret these factors across groups? Or, is it more to stress this “inflation” with the group-specific adjustment factor for a low-vaccination-group? That inflation factor, however, will be lower than the overall inflation factor…
__Adjusted(***) based on full vaccination__: population at risk = population minus 85% of people who received complete doses (2 PFR/MOD or 1 JSN) 14 days ago. Real-world effectiveness for full vaccination is 90% for PFR/MOD 14 days after the second shot. Since Harford county residents received predominantly PFR/MOD vaccine, 85% is applied to be conservative.
COVID-19 case by background characteristics data are as of June 6, 2021.
(Note: Age-disaggregated COVID-19 case data came from Redcap - as of 6/6/2020)
(Note: Race/ethnicity-disaggregated COVID-19 case data came from Redcap - as of 6/6/2020. But, about 10% of cases do not have race/ethnicity information in Redcap)
###Annex: WAPO Methodology
"The Post adjusted covid-19 rates for cases, deaths and hospitalization over time by combining Centers for Disease Control and Prevention data on cases, hospitalization and vaccinations. The Post used a rolling seven-day average of daily cases, deaths and hospitalization. For vaccination, The Post used the number of people who had received at least one shot as of each date.
For events like covid-19 infection, rates are usually calculated by dividing the number of cases by the number of people in the population. For example, if there are 12 cases among a population of 100 people, the rate would be 12 people per 100. The Post reduced the denominator to exclude most vaccinated people. So if 20 people got vaccinated, that would mean there were 12 cases out of the remaining 80 unvaccinated people, for an adjusted rate of 15 cases per 100 people.
Vaccination is not perfect in preventing infections, however, so The Post did not subtract the entire population of vaccinated people. Data shows vaccines are about 90 percent effective in preventing cases among people who have received the shot. Cases among vaccinated people are called breakthrough cases. To be conservative, The Post estimated that up to 15 percent of the vaccinated population could still be infected.
So, in the example above, instead of removing all 20 vaccinated people, The Post removed 17. That would leave 12 cases among 83 people, for an adjusted rate of 14.5 cases per 100 people.
The Post calculated the adjusted rates of cases, deaths and hospitalization for the nation and each state since the start of vaccination in December. Covid-19 case and death rates released by states are sometimes subject to time lags. State also sometimes review older cases and issue updated figures that reflect a backlog of old cases rather than a surge on that day."
Source: (https://www.washingtonpost.com/health/interactive/2021/covid-rates-unvaccinated-people/)
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