Table 3.
Absolute risk reductions and numbers needed to be vaccinated (NNVs) in geographical regions with different baseline risks, population-based data Symptom development
| 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% or 66% effectiveness (RRR 95% or 66%) (D×5% or 34%) (%)‡ | F. Absolute risk reduction (D−E) (%) | G. Number needed to be vaccinated |
| May 2021 | ||||||
| Los Angeles, California | 270.43 | 135.22 | 0.14 | 0.01 | 0.13 (0.06 to 0.20) | 769 (498 to 1688) |
| Hampshire, Massachusetts | 251 | 125.5 | 0.13 | 0.01 | 0.12 (0.05 to 0.18) | 833 (529 to 1951) |
| Putnam, New York | 164 | 82 | 0.08 | 0.00 | 0.08 (0.03 to 0.13) | 1250 (751 to 3728) |
| 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 | 3.13 | 0.16 | 2.97 (2.6 to 3.32) | 34 (30 to 38) |
| Uttar Pradesh state, India | 833 | 416.5 | 0.42 | 0.02 | 0.40 (0.27 to 0.53) | 250 (189 to 370) |
| Kerala state, India | 7143.00 | 3571.5 | 3.57 | 0.18 | 3.39 (3.02 to 3.76) | 29 (27 to 33) |
| September 2021 | ||||||
| Los Angeles, California | 472 | 236 | 0.24 | 0.08 | 0.16 (0.01 to 0.27) | 625 (369 to 2031) |
| Hampshire, Massachusetts | 228 | 114 | 0.11 | 0.04 | 0.07 (0.00 to 0.11) | 1429 (686 to –17 022) |
| Putnam, New York | 341 | 170.5 | 0.17 | 0.06 | 0.11 (0.01 to 0.20) | 909 (490 to 6223) |
| De Baca, New Mexico | 409 | 204.5 | 0.20 | 0.07 | 0.13 (0.02 to 0.23) | 769 (431 to 3541) |
| McKinley, New Mexico | 517 | 258.5 | 0.26 | 0.09 | 0.17 (0.05 to 0.29) | 588 (350 to 1846) |
| Catron, New Mexico | 405 | 202.5 | 0.20 | 0.07 | 0.13 (0.03 to 0.23) | 769 (431 to 3541) |
| Ladakh territory, India | 28 | 14 | 0.01 | 0.00 | 0.01 (0.01 to 0.01) | 10 000 (3379 to –10 418) |
| Uttar Pradesh state, India | 14 | 7 | 0.01 | 0.00 | 0.01 (0.01 to 0.01) | 10 000 (3379 to –10 418) |
| Kerala state, India | 1204 | 602 | 0.60 | 0.20 | 0.40 (0.23 to 0.58) | 250 (174 to 444) |
95% CIs shown in parentheses. CIs that include negative numbers or infinity indicate non-significant differences in harm 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.28
*Sources: Johns Hopkins dashboard (https://www.arcgis.com/apps/MapSeries/index.html?appid=ad46e587a9134fcdb43ff54c16f8c39b) and 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 based on published research and a published systematic review and meta-analysis.36–39 Further explanation in text. Online supplemental table 3 presents sensitivity analyses assuming 25% and 80% symptom development rates.
‡Reported effectiveness of the most effective vaccines (RRR) decreased from the range of 95% during May 2021 to the range of 66% during September 2021, based mainly on the emergence of the Delta variant.57
RRR, relative risk reduction.