Effectiveness of mRNA vaccines and waning of protection against SARS-CoV-2 infection and severe covid-19 during predominant circulation of the delta variant in Italy: retrospective cohort study

Abstract

Objectives To estimate the effectiveness of mRNA vaccines against SARS-CoV-2 infection and severe covid-19 at different time after vaccination. Design Retrospective cohort study. Setting Italy, 27 December 2020 to 7 November 2021. Participants 33 250 344 people aged ≥16 years who received a first dose of BNT162b2 (Pfizer-BioNTech) or mRNA-1273 (Moderna) vaccine and did not have a previous diagnosis of SARS-CoV-2 infection. Main outcome measures SARS-CoV-2 infection and severe covid-19 (admission to hospital or death). Data were divided by weekly time intervals after vaccination. Incidence rate ratios at different time intervals were estimated by multilevel negative binomial models with robust variance estimator. Sex, age group, brand of vaccine, priority risk category, and regional weekly incidence in the general population were included as covariates. Geographic region was included as a random effect. Adjusted vaccine effectiveness was calculated as (1−IRR)×100, where IRR=incidence rate ratio, with the time interval 0-14 days after the first dose of vaccine as the reference. Results During the epidemic phase when the delta variant was the predominant strain of the SARS-CoV-2 virus, vaccine effectiveness against SARS-CoV-2 infection significantly decreased (P<0.001) from 82% (95% confidence interval 80% to 84%) at 3-4 weeks after the second dose of vaccine to 33% (27% to 39%) at 27-30 weeks after the second dose. In the same time intervals, vaccine effectiveness against severe covid-19 also decreased (P<0.001), although to a lesser extent, from 96% (95% to 97%) to 80% (76% to 83%). High risk people (vaccine effectiveness −6%, −28% to 12%), those aged ≥80 years (11%, −15% to 31%), and those aged 60-79 years (2%, −11% to 14%) did not seem to be protected against infection at 27-30 weeks after the second dose of vaccine. Conclusions The results support the vaccination campaigns targeting high risk people, those aged ≥60 years, and healthcare workers to receive a booster dose of vaccine six months after the primary vaccination cycle. The results also suggest that timing the booster dose earlier than six months after the primary vaccination cycle and extending the offer of the booster dose to the wider eligible population might be warranted.

Analysis of severe illness after post-vaccination COVID-19 breakthrough among adults with and without HIV in the United States

“…Sex, age, comorbidities, and additional vaccine doses impact the risk of severe COVID-19 breakthrough illness. 10,[31][32][33] Among both PWoH and PWH, increasing age was the most significant risk factor for severe COVID-19 breakthrough illness in our study. Female PWoH had reduced risk, which has been previously documented; [34][35][36] however, female PWH had increased severe risk.…”

“…Among PWoH, several comorbidities have been associated with increased severe COVID-19 breakthrough illness risk. 32,33,39 Our findings suggest an increased risk with HTN, ESRD, and SOT. Comorbidities were prevalent among those who experienced a severe COVID-19 breakthrough illness with 90% having a diagnosis of obesity, DM, HTN or ESRD.…”

“…Among PWoH, several comorbidities have been associated with increased severe COVID-19 breakthrough illness risk. 32,33,39 Our findings suggest an increased risk with HTN, ESRD, and SOT.…”

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.…”

Effectiveness of a nation-wide COVID-19 vaccination program in Mexico

“…We also report on a reduction in VE against SARS-CoV-2 infection and COVID-19 related hospitalization and death for most evaluated vaccines in older adults and persons living with diabetes. Previous data had shown that waning of vaccine-induced immunity was associated with increased age and comorbidity 42 . Our observations of reduced vaccines effectiveness in people living with diabetes also supports previous evidence which reported reduced neutralizing antibody response and immunogenicity were observed in people with diabetes 43 .…”