Single-dose mRNA vaccine effectiveness against SARS-CoV-2, including P.1 and B.1.1.7 variants: a test-negative design in adults 70 years and older in British Columbia, Canada

Abstract

Introduction: Randomized-controlled trials of mRNA vaccine protection against SARS-CoV-2 included relatively few elderly participants. We assess singe-dose mRNA vaccine effectiveness (VE) in adults ≥70-years-old in British Columbia (BC), Canada where the second dose was deferred by up to 16 weeks and where a spring 2021 wave uniquely included co-dominant circulation of B.1.1.7 and P.1 variants of concern (VOC). Methods: Analyses included community-dwelling adults ≥70-years-old with specimen collection between April 4 (epidemiological week 14) and May 1 (week 17). Adjusted VE was estimated by test-negative design through provincial laboratory and immunization data linkage. Cases were RT-PCR test-positive for SARS-CoV-2 and controls were test-negative. Vaccine status was defined by receipt of a single-dose ≥21 days before specimen collection, but a range of intervals was assessed. In variant-specific analyses, test-positive cases were restricted to those genetically-characterized as B.1.1.7, P.1 or non-VOC. Results: VE analyses included 16,993 specimens: 1,226 (7.2%) test-positive cases and 15,767 test-negative controls. Of 1,131 (92%) viruses genetically categorized, 509 (45%), 314 (28%) and 276 (24%) were B.1.1.7, P.1 and non-VOC lineages, respectively. VE was negligible at 14% (95% CI 0-26) during the period 0-13 days post-vaccination but increased from 43% (95% CI 30-53) at 14-20 days to 75% (95% CI 63-83) at 35-41 days post-vaccination. VE at ≥21 days was 65% (95% CI 58-71) overall: 72% (95% CI 58-81), 67% (95% CI 57-75) and 61% (95% CI 45-72) for non-VOC, B.1.1.7 and P.1, respectively. Conclusions: A single dose of mRNA vaccine reduced the risk of SARS-CoV-2 in adults ≥70-years-old by about two-thirds, with protection only minimally reduced against B.1.1.7 and P.1 variants. Substantial single-dose protection in older adults reinforces the option to defer the second dose when vaccine supply is scarce and broader first-dose coverage is needed.

Effectiveness of the WHO-Authorized COVID-19 Vaccines: A Rapid Review of Global Reports till 30 June 2021

“…The results of the quality assessment of all the included studies are shown in Supplementary Table S2. Before 1 July 2021, 24 of 39 studies were published in peer-reviewed journals [9,12,[15][16][17]19,22,24,25,[28][29][30][31]33,34,36,37,[40][41][42]45,47,48,50] while the remaining 15 studies were posted online as preprint articles [11,18,20,21,23,26,27,32,35,38,39,43,44,46,49]. The characteristics of the studies are shown in Supplementary Table S1, including the country, study design, types of vaccines, outcomes, and SARS-CoV-2 variants involved in the studies.…”

“…The outcomes include all laboratory-confirmed SARS-CoV-2 infection, asymptomatic and symptomatic infection, hospitalization, critical disease, and death. As for evaluating the protective effects of the vaccine on SARS-CoV-2 variants, 5 studies mentioned the approximate prevalence of variants in the region of the study population [18,19,28,34,49], and 11 studies calculated the number or percentage of cases with variants among all or sampled participants with a positive test of SARS-CoV-2 variants [20,26,31,33,[36][37][38]42,43,46,48]. Only three studies evaluated the VE against specific VOC, in which one study from Qatar reported the VE against B.1.1.7 and B.1.351 [9], one study from Canada studied VE against B.1.1.7 and P.1 [46], and the other one study from the UK evaluated the VE against B.1.1.7 and B.1.617.2 (delta variant) [20].…”

“…As for evaluating the protective effects of the vaccine on SARS-CoV-2 variants, 5 studies mentioned the approximate prevalence of variants in the region of the study population [18,19,28,34,49], and 11 studies calculated the number or percentage of cases with variants among all or sampled participants with a positive test of SARS-CoV-2 variants [20,26,31,33,[36][37][38]42,43,46,48]. Only three studies evaluated the VE against specific VOC, in which one study from Qatar reported the VE against B.1.1.7 and B.1.351 [9], one study from Canada studied VE against B.1.1.7 and P.1 [46], and the other one study from the UK evaluated the VE against B.1.1.7 and B.1.617.2 (delta variant) [20]. The characteristics of the studies and their VE estimates with 95% CI against overall SARS-CoV-2 infection among general and specific populations are shown in Table 1 and the distributions of the VE estimates are shown in Figure 2.…”

“…The characteristics of the studies and their VE estimates with 95% CI against overall SARS-CoV-2 infection among general and specific populations are shown in Table 1 and the distributions of the VE estimates are shown in Figure 2. Among the partially vaccinated general population, the VE varied among studies (42-78% by BNT162b2 [23,28,31,32,40,42,46], 67-93% by mRNA-1273 [26,31,40], and 61-95% by ChAdOx1 [31,32,42]). After full vaccination, the VE was all higher than 75% (77-98% by BNT162b2 [11,23,28,31,33,40,42], 93-99% by mRNA-1273 [31,40], 79% by ChAdOx1 [42], and 78% by Ad26.COV2.S with a single dose as full vaccination [27]).…”

“…Three studies specifically calculated the VE against the VOC [9,20,46] (Table 1, Figure 4). For the Alpha variant (B.1.1.7), one dose of BNT162b2 or ChAdOx1 provided around 50% of VE on symptomatic infection and critical disease or death [9,32].…”