Table 1.
Summary of Scenarios Explored. The values in bold represent the default parameters, unless otherwise stated.
| Parameter | Values | References / Notes |
|---|---|---|
| Income setting | High-income (HIC); Upper-middle income (UMIC); Lower-middle income (LMIC); Low-income (LIC) | [16] |
| Transmission from March 2020 - April 2020 (R0) | 2.5; 1.5–4.0 | Assumed values to mimic patterns of epidemics observed globally |
| Transmission from May 2020 - January 2021 (Rt1) | 1.1; 0.9; 1.3 | |
| Transmission from February 2021 onwards (Rt2) | 2.0; 1.5; 2.5 | |
| Vaccine mode of action | Combined; Infection; Disease | [2], [3], [4], [5], [6], [29] |
| Vaccine efficacy against infection | 90%; 50–90%; 0% (disease-only efficacy) | [3], [4], [5], [6] |
| Vaccine efficacy against disease | Additional 60% for breakthrough infections; 50–90% (disease-only efficacy); 0% (infection-only efficacy) | [3], [5], [25], [26], [27], [28] |
| Reduction in efficacy against infection in individuals 65 years and older due to immunosenescence | 0%; 50% | [44], [45] |
| Vaccine coverage | 80%; 0%–100% | [58] |
| Vaccine duration of protection | Long-term; 1 year; 6 months | [38] |
| Duration of naturally-acquired immunity | 1 year; lifelong; 6 months | [35], [36], [37], [59], [60] |
| Age targeting | All ages targeted; Older; Younger; combinations of 5-year groups | Chosen to reflect different patterns being adopted by countries |
| Duration between vaccination and vaccine protection following second dose | 7 days | [30], [31], [32], [33], [34] |
| Health system constraints | Present; Absent | [15] |
| Health system constraint assumptions |
Health system constraints present (LIC: Capacity limited + negative health outcomes due to poorer standard of care LMIC: Capacity limited UMIC & HIC: Capacity unlimited as surge capacity is put in place); Health system constraints absent (Capacity unlimited in all settings) |
[15] |
| Vaccine dose supply constraint | 2 billion doses in 2021 (COVAX); 2 billion doses in 2021 + direct country procurement (1.15 billion doses by HICs, 1.10 billion doses by MICs) | [7] |
| Dose schedule | 2 doses; 1 dose | [2], [4], [5], [6] |
| Vaccine buffer stock and wastage allowance | 15% | [42] |