Risk factors affecting COVID-19 vaccine effectiveness identified from 290 cross-country observational studies until February 2022: a meta-analysis and meta-regression

Abstract

Background Observational studies made it possible to assess the impact of risk factors on the long-term effectiveness of mRNA and adenoviral vector (AdV) vaccines against COVID-19. Methods A computerized literature search was undertaken using the MEDLINE, EMBASE, and MedRxiv databases to identify eligible studies, with no language restrictions, published up to 28 February 2022. Eligible were observational studies assessing vaccine effectiveness (VE) by disease severity with reference groups of unvaccinated participants or participants immunized with one, two, or three vaccine doses. Our study was carried out in compliance with the PRISMA and MOOSE guidelines. The risk of study bias was identified using the Newcastle–Ottawa Quality Assessment Scale. The GRADE guidelines were applied to assess the strength of evidence for the primary outcome. The synthesis was conducted using a meta-analysis and meta-regression. Results Out of a total of 14,155 publications, 290 studies were included. Early VE of full vaccination against COVID-19 of any symptomatology and severity decreased from 96% (95% CI, 95–96%) for mRNA and from 86% (95% CI, 83–89%) for AdV vaccines to 67% for both vaccine types in the last 2 months of 2021. A similar 1-year decline from 98 to 86% was found for severe COVID-19 after full immunization with mRNA, but not with AdV vaccines providing persistent 82–87% effectiveness. Variant-reduced VE was only associated with Omicron regardless of disease severity, vaccine type, or vaccination completeness. The level of protection was reduced in participants aged >65 years, with a comorbidity or those in long-term care or residential homes independently of the number of doses received. The booster effect of the third mRNA dose was unclear because incompletely restored effectiveness, regardless of disease severity, declined within a short-term interval of 4 months. Conclusions Full vaccination provided an early high, yet waning level of protection against COVID-19 of any severity with a strong impact on the high-risk population. Moreover, the potential risk of new antigenically distinct variants should not be underestimated, and any future immunization strategy should include variant-updated vaccines.

The Prospective COVID-19 Post-Immunization Serological Cohort in Munich (KoCo-Impf): Risk Factors and Determinants of Immune Response in Healthcare Workers

“…As vaccine protection diminishes over time, receiving an early vaccination reduces the risk of early infection but may increase the risk of later infection. This has been noted in several studies [ 9 , 10 , 11 ].…”

Vaccination status and outcomes in critical COVID-19 patients

“…Multiple factors may contribute to the fact that vaccination does not protect against critical COVID-19, including age, vaccine type, virus variant, and immunosuppression. 26 In addition, other, unknown, factors may contribute to the lack of vaccine efficacy in vaccinated patients presenting with severe COVID-19. Despite these findings, in the absence of a statistically significant difference, it is important to note that the proportions of patients with severe complications, NIV failure, and in-hospital mortality were higher in unvaccinated patients than in those who had received at least one dose of vaccine in the propensity-matched sample.…”

“…pacientes não vacinados a pacientes que receberam pelo menos uma dose de vacina, mostrou um melhor prognóstico em pacientes com vacinação completa ou incompleta. Múltiplos fatores podem contribuir para o fato de a vacinação não proteger contra a COVID-19 crítica, incluindo a idade, o tipo de vacina, a variante do vírus e a imunossupressão (26). Além disso, outros fatores desconhecidos podem contribuir para a falta de eficácia da vacina em pacientes vacinados com COVID-19 grave.…”

COVID-19 and metabolic syndrome

“…Proportion of individuals producing neutralizing humoral immunity after vaccination was lower among people with obesity compared to those without [47] . A meta-analysis of observational studies reported that presence of one or more comorbidities (including obesity, diabetes, hypertension) was associated with lower protection against COVID-19 and severe COVID-19 [48] . Immunogenicity of vaccines appear to be lower in people with diabetes irrespective of the type of vaccine and weaker with higher BMI and worse glucose control [49] .…”