High vaccine effectiveness against severe Covid-19 in the elderly in Finland before and after the emergence of Omicron

Abstract

Background. The elderly are highly vulnerable to severe Covid-19. Waning immunity and emergence of Omicron have caused concerns about reduced effectiveness of Covid-19 vaccines. The objective was to estimate vaccine effectiveness (VE) against severe Covid-19 among the elderly. Methods. This nationwide, register-based cohort study included all residents aged 70 years and over in Finland. The follow-up started on December 27, 2020, and ended on February 19, 2022. The study outcomes were Covid-19-related hospitalization and intensive care unit (ICU) admission timely associated with SARS-CoV-2 infection. VE was estimated as 1 minus the hazard ratio comparing the vaccinated and unvaccinated and taking into account time since vaccination. Omicron-specific VE was evaluated as the effectiveness observed since January 01, 2022. Results. The cohort included 897932 individuals. Comirnaty (BioNTech/Pfizer) VE against Covid-19-related hospitalization was 93% (95% confidence interval [CI], 90%-95%) and 87% (84%-89%) 14-90 and 91-180 days after the second dose; VE increased to 96% (95%-97%) 14-60 days after the third dose. VE of other homologous and heterologous 3-dose series was similar. Protection against severe Covid-19 requiring ICU treatment was even better. Since January 01, 2022, Comirnaty VE was 91% (95% CI, 79%-96%) and 76% (56%-86%) 14-90 and 91-180 days after the second and 95% (94%-97%) 14-60 days after the third dose. Conclusions. VE against severe Covid-19 is high among the elderly. It waned slightly after 2 doses, but a third restored the protection. VE against severe Covid-19 remained high even after the emergence of Omicron.

mRNA vaccine effectiveness against hospitalisation due to severe acute respiratory infection (SARI) COVID-19 during Omicron variant predominance estimated from real-world surveillance data, Slovenia, February to March 2022

“…In contrast to our results, waning of protection against Omicron-related COVID-19 hospitalisation with time since vaccination with either two or three doses was reported by some [ 7 , 11 , 12 ], while strong and durable protection after the second mRNA dose and even more robust protection after a booster dose was also reported by a recent study from Qatar [ 13 ].…”

“…Understanding how much longer the high protection against Omicron-related SARI COVID-19 hospitalisation will last, will only be possible in the future, when the number of people vaccinated with the third dose more than 6 months ago will accumulate. Similar results with respect to protection against hospitalisation due to Omicron-related COVID-19 for elderly individuals (aged 70 years and older) were reported from Finland (VE of 91% and 76%, 14–90 and 91–180 days after second dose, and 95%, 14–60 days after third dose) [ 11 ].…”

Comparison of the Effectiveness and Safety of Heterologous Booster Doses with Homologous Booster Doses for SARS-CoV-2 Vaccines: A Systematic Review and Meta-Analysis

“…Among the 121 studies under full-text review, 98 studies were excluded. Eventually, 23 studies (including 13 published articles and 10 preprints) were included in this meta-analysis based on the inclusion criteria [ 14 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 ]. The literature retrieval flow chart is shown in Figure 1 .…”

Protection of homologous and heterologous boosters after primary schemes of rAd26-rAd5, ChAdOx1 nCoV-19 and BBIBP-CorV during the Omicron outbreak in adults of 50 years and older in Argentina: a test-negative case-control study

“…[7][8][9][10]12,13,[15][16][17][18] In addition, this study provides new information on the utilisation of the inactivated vaccine BBIBP-CorV, the viral vector vaccine rAd26-rAd5, and heterologous primary schemes, which was previously quite scarce. 19 After realizing that ChAdOx1 nCoV-19 administration was associated with increased risk of thrombosis with thrombocytopenia syndrome, some European Union Member…”

“…Similar results were reported with heterologous boosting after the administration of primary schemes with the inactivated vaccine Sinovac and the vectored vaccines Ad26.COV2-S and ChAdOx1 nCoV-19. 13,15,[17][18][19][20] Although our results are the first to report protection in a real-life setting, they are in line with in vitro studies: Argentinian researchers found that a heterologous booster with ChAdOx1 nCoV-19, rAd26-rAd5, or BNT162b2 vaccines markedly increased the neutralising activity against the Omicron variant and was maintained up to 90 days in older people with primary schemes of BBIBP-CorV. 8 Furthermore, researchers from Bahrein and Serbia reported that heterologous 11 boosting with Pfizer-BioNTech after administering a primary scheme with rAd26-rAd5 yielded higher levels of antibodies than homologous boosting.…”