Age and product dependent vaccine effectiveness against SARS-CoV-2 infection and hospitalisation among adults in Norway: a national cohort study, July – November 2021

Abstract

Background: COVID-19 vaccines have been crucial in the pandemic response and understanding changes in vaccines effectiveness is essential to guide vaccine policies. Though the Delta variant is no longer dominant, understanding vaccines effectiveness properties will provide essential knowledge to comprehend the development of the pandemic and estimate potential changes over time. Methods: In this population-based cohort study, we estimated vaccine effectiveness against SARS-CoV-2 infections, hospitalisations, intensive care admissions, and death using Cox proportional hazard models, across different vaccine product regimens and age groups, between 15 July and 31 November 2021 (Delta variant period). Vaccine status is included as a time-varying covariate and all models were adjusted for age, sex, comorbidities, county of residence, country of birth, and living conditions. Data from the entire adult Norwegian population were collated from the National Preparedness Register for COVID-19 (Beredt C19). Results: The overall adjusted vaccine effectiveness against infection decreased from 81.3% (confidence interval (CI): 80.7 to 81.9) in the first two to nine weeks after receiving a second dose to 8.6% (CI:4.0 to 13.1) after more than 33 weeks, compared to 98.6% (CI: 97.5 to 99.2) and 66.6% (CI: 57.9 to 73.6) against hospitalisation respectively. After the third dose (booster), the effectiveness was 75.9% (CI: 73.4 to 78.1) against infection and 95.0% (CI: 92.6 to 96.6) against hospitalisation. Spikevax or a combination of mRNA products provided the highest protection, but the vaccine effectiveness decreased with time since vaccination for all vaccine regimens. Conclusions: Even though the vaccine effectiveness against infection wanes over time, all vaccine regimens remained effective against hospitalisation after the second vaccine dose. For all vaccine regimens, a booster facilitated recovery of effectiveness. The results from this support the use of heterologous schedules, increasing flexibility in vaccination policy.

Waning of vaccine effectiveness against moderate and severe covid-19 among adults in the US from the VISION network: test negative, case-control study

“…Our results are also consistent with other reports of waning protection after three mRNA doses 232425. As with others, we noted less waning against more severe outcomes,326 lower vaccine effectiveness among individuals who were immunocompromised,1727 and higher vaccine effectiveness among recipients of mRNA-1273 compared with recipients of BNT162b2 102324. We also observed improvement in vaccine effectiveness after a fourth dose 28…”

“…Our vaccine effectiveness estimates for mRNA vaccines are broadly consistent with those in other reports: vaccine effectiveness was lower against the omicron variant than earlier variants,102122 vaccine effectiveness waned after a second dose,3456789 and a third dose restored high levels of protection against severe covid-19 during the omicron and delta periods 10111213. Our results are also consistent with other reports of waning protection after three mRNA doses 232425. As with others, we noted less waning against more severe outcomes,326 lower vaccine effectiveness among individuals who were immunocompromised,1727 and higher vaccine effectiveness among recipients of mRNA-1273 compared with recipients of BNT162b2 102324.…”

Investigating COVID-19 Vaccine Impact on the Risk of Hospitalisation through the Analysis of National Surveillance Data Collected in Belgium

“…RR estimates obtained using a retrospective 4-week sliding window are reported in Figure 1, and estimates obtained for larger periods are reported in Table S2. As shown in both Figure 1 and Table S2, our results also confirm notable variations in the apparent protective effect of the vaccine between different age categories, with the RR estimates increasing globally with age [21][22][23]. In particular, sliding window estimates (Figure 1) indicate that at the beginning of the study period, RR estimates started rather high for people above 75 years old (75-85: RR = 0.34, 95% CI = [0.27-0.42]; 85+: RR = 0.65, 95% CI = [0.48-0.87]), which is compatible with an effect of waning immunity, the vaccination campaign for these two age categories having started early 2021.…”

Effectiveness of COVID-19 Vaccines Over Time Prior to Omicron Emergence in Ontario, Canada: Test-Negative Design Study

“…To our knowledge, few studies have evaluated the effectiveness of heterologous 2-dose schedules. Two other studies also found that heterologous and homologous mRNA vaccine schedules had equivalent VE estimates [ 11 , 24 ]. A Danish study found that VE against any infection for heterologous ChAdOx1 and mRNA vaccine schedules was 88% (95% CI, 83%–92%) ≥14 days after the second dose, which is comparable to our VE estimates against any infection at 7–59 days (VE ChAdOx1/BNT162b2 = 90% [95% CI, 88%–92%]; VE ChAdOx1/mRNA-1273 = 91% [95% CI, 89%–93%]), but did not assess duration of effectiveness [ 20 ].…”