Cohort study of Covid-19 vaccine effectiveness among healthcare workers in Finland, December 2020 - October 2021

Abstract

Recently, Covid-19 vaccine effectiveness has decreased especially against mild disease due to emergence of the Delta variant and waning protection. In this register-based study among healthcare workers in Finland, the vaccine effectiveness of two-dose mRNA vaccine series against SARS-CoV-2 infection decreased from 82% (95% CI 79-85%) 14-90 days after vaccination to 53% (43-62%) after 6 months. Similar trend was observed for other series. Waning was not observed against Covid-19 hospitalization. These results facilitate decision-making of booster doses for healthcare workers.

Symptoms and severity in vaccinated and unvaccinated patients hospitalised with SARS-CoV-2 delta (B.1.617.2) variant infection

“…Recent studies showed 86-88% vaccine-associated reduction in the hospital admission rate in those infected with the delta VOC 19–21 ; Our observations confirm the positive impact of vaccination on the severity of the SARS-CoV-2 delta infection, even in hospitalised patients. Moreover, we observed that the positive impact was maintained in populations at risk of severe Covid-19: those aged over 65 years, and those with pre-existing cardiac failure, kidney failure, or a chronic respiratory disease (at least for one or several severity criteria).…”

Duration of effectiveness of vaccines against SARS-CoV-2 infection and COVID-19 disease: results of a systematic review and meta-regression

“…Three studies were randomised controlled trials 19 , 20 , 21 and 15 were post-introduction observational studies (seven were test-negative design case-control studies, six were retrospective studies, and two were prospective cohort studies; table 1 ). 10 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 Studies were done in Canada (one study), Finland (one study), Israel (one study), Qatar (one study), Spain (one study), Sweden (one study), the UK (two studies), the USA (eight studies), and in addition two multicountry clinical trials were carried out. The Canadian study included separate results for Quebec and British Columbia; therefore, the results for each province were considered separately for this review.…”

“…12 studies evaluated the vaccine efficacy or effectiveness over time for severe COVID-19 disease, among which there were 36 vaccine-specific analyses (Pfizer–BioNTech-Comirnaty, n=19; Moderna-mRNA-1273, n=10; Janssen-Ad26.COV2.S, n=4; AstraZeneca-Vaxzevria, n=3; table 1 ). 10 , 21 , 22 , 24 , 25 , 27 , 28 , 29 , 31 , 32 , 33 , 34 13 vaccine-specific analyses took place in single-variant settings (11 in delta settings and two in Alpha settings), and 23 analyses took place in mixed-variant settings. 22 vaccine-specific analyses were done among people of all ages and 14 among older people.…”

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

“…Our findings are consistent with other studies investigating waning of vaccine effectiveness, as summarised through a systematic review by Feikin et al 21 Most observational studies employ a testnegative study design, while some are register-based cohort studies like ours. 19,[25][26][27][28][29][30][31][32][33] We reported large waning of effectiveness against SARS-CoV-2 infection, which could have several explanations. First, we have a longer follow-up time than previously published studies.…”