Numbers needed to be vaccinated in geographical areas with different baseline risks
| May 2021 | ||||||
| (A) County, state or territory | (B) Active cases per 100 000 population* | (C) Calculated active symptomatic cases per 100 000 (estimated at 50% of cases) (B×50%)† | (D) Calculated active symptomatic cases per 100 000 (expressed as %)=baseline risk (C/100 000)(%) | (E) Calculated risk of symptomatic disease after vaccine with 95% effectiveness (RRR 95%) (D×5%)(%) | (F) Absolute risk reduction (ARR) (D–E)(%) | (G) Number needed to be vaccinated (NNV) (1/F) |
| De Baca, New Mexico | 1124.74 | 562.37 | 0.56 | 0.03 | 0.53 (0.40 to 0.60) | 200 (166 to 252) |
| McKinley, New Mexico | 730.89 | 365.45 | 0.37 | 0.02 | 0.35 (0.25 to 0.45) | 286 (223 to 398) |
| Catron, New Mexico | 80.95 | 40.48 | 0.04 | 0.00 | 0.04 (0.00 to 0.08) | 2500 (1275 to 62 792) |
| Ladakh territory, India | 6250.00 | 3125.00 | 3.13 | 0.16 | 2.97 (2.60 to 3.32) | 34 (30 to 38) |
| Uttar Pradesh state, India | 833.00 | 416.50 | 0.42 | 0.02 | 0.40 (0.27 to 0.53) | 250 (189 to 370) |
| Kerala state, India | 7143.00 | 3571.50 | 3.57 | 0.18 | 3.39 (3.02 to 3.76) | 29 (27 to 33) |
| September 2021 | ||||||
| (A) County, state or territory | (B) Active cases per 100 000 population* | (C) Calculated active symptomatic cases per 100 000 (estimated at 50% of cases) (B×50%)† | (D) Calculated active symptomatic cases per 100 000 (expressed as %)=baseline risk (C/100 000)(%) | (E) Calculated risk of symptomatic disease after vaccine with 66% effectiveness (RRR 66%) (D×34%)(%)‡ | (F) Absolute risk reduction (ARR) (D–E)(%) | (G) Number needed to be vaccinated (NNV) (1/F) |
| De Baca, New Mexico | 409.00 | 204.50 | 0.20 | 0.07 | 0.13 (0.03 to 0.23) | 769 (431 to 3541) |
| McKinley, New Mexico | 517.00 | 258.50 | 0.26 | 0.09 | 0.17 (0.05 to 0.29) | 588 (350 to 1846) |
| Catron, New Mexico | 405.00 | 202.50 | 0.20 | 0.07 | 0.13 (0.03 to 0.23) | 769 (431 to 3541) |
| Ladakh territory, India | 28.00 | 14.00 | 0.01 | 0.00 | 0.01 (0.00 to 0.01) | 10 000 (3379 to −10 418) |
| Uttar Pradesh state, India | 14.00 | 7.00 | 0.01 | 0.00 | 0.01 (0.00 to 0.01) | 10 000 (3379 to −10 418) |
| Kerala state, India | 1204.00 | 602.00 | 0.60 | 0.20 | 0.40 (0.23 to 0.58) | 250 (174 to 444) |
95% CI shown in parentheses. CIs that overlap 0 occur with very low absolute risk reductions and indicate non-significant differences between the intervention and control groups. Such intervals do not necessarily include the point estimates and reflect a range from beneficial to harmful effects of the intervention.27
*Sources: Johns Hopkins dashboard, https://www.arcgis.com/apps/MapSeries/index.html?appid=ad46e587a9134fcdb43ff54c16f8c39b (accessed 23 May 2021 and 5 September 2021); New York Times dashboard, https://www.nytimes.com/interactive/2020/world/asia/india-coronavirus-cases.html (accessed 23 May 2021 and 5 September 2021).
†Estimate of percentage of infections that become symptomatic are based on published research and a published systematic review and meta-analysis.28–30 Sensitivity analyses based on the range of percentages in published research are available from the authors on request.
‡Reported effectiveness of the most effective vaccines dropped to the range of 66% based mainly on the emergence of the Delta variant.20
RRR, relative risk reduction.