Table 2.
Herd immunity thresholds in terms of the critical prevalence of protected individuals (Ic), critical vaccination coverage (Vc), the percentage of susceptible individuals in vaccinated populations, and the critical prevalence of positive anti-measles serologic results (pc) for measles viruses with basic reproductive numbers (Ro) ranging from 6 to 60.
| Measles VirusRo | Critical Prevalence of Protected Individuals a Ic (%) | Measles Vaccination | Critical Prevalence of Positive Serologic Results d pc (%) | |
|---|---|---|---|---|
| Critical Vaccination Coverage b Vc (%) | Susceptible Individuals c (%) | |||
| 6 | 83.3 | 87.7 | 16.7 | 81.3 |
| 7 | 85.7 | 90.2 | 14.3 | 83.6 |
| 8 | 87.5 | 92.1 | 12.5 | 85.3 |
| 9 | 88.9 | 93.6 | 11.1 | 86.6 |
| 10 | 90.0 | 94.7 | 10.0 | 87.6 |
| 11 | 90.9 | 95.7 | 9.1 | 88.5 |
| 12 | 91.7 | 96.5 | 8.3 | 89.2 |
| 13 | 92.3 | 97.2 | 7.7 | 89.8 |
| 14 | 92.9 | 97.7 | 7.1 | 90.3 |
| 15 | 93.3 | 98.2 | 6.7 | 90.7 |
| 16 | 93.8 | 98.7 | 6.2 | 91.1 |
| 17 | 94.1 | 99.1 | 5.9 | 91.5 |
| 18 | 94.4 | 99.4 | 5.6 | 91.8 |
| 19 | 94.7 | 99.7 | 5.3 | 92.1 |
| 20 | 95.0 | 100 | 5 | 92.3 |
| 21 | 95.2 | − | 5 | 92.5 |
| 22 | 95.5 | − | 5 | 92.7 |
| 23 | 95.7 | − | 5 | 92.9 |
| 24 | 95.8 | − | 5 | 93.1 |
| 25 | 96.0 | − | 5 | 93.2 |
| 30 | 96.7 | − | 5 | 93.9 |
| 40 | 97.5 | − | 5 | 94.7 |
| 50 | 98.0 | − | 5 | 95.1 |
| 60 | 98.3 | − | 5 | 95.4 |
a Ic = 1 − (1/Ro), b Vc = Ic/E. Assuming 95% effectiveness (E) of 95% for measles vaccination. c Percentage of susceptible individuals = 100 − (Vc E), d pc = Ic Se + [(1 − Ic) (1 − Sp)]. Assuming 97% sensitivity (Se) and 97% specificity (Sp) for measles serological tests.