Boosters and time since last anti-COVID-19 vaccine dose: lead public health choices by real-time epidemiological assessment

BACKGROUND: the levels of anti-SARS-CoV-2 antibodies after the second vaccine dose decline in the following months;an additional vaccine dose (booster) is able to swiftly restore the immune system, significantly reducing the risk of severe disease. In the winter of 2021, a new, particularly infectious variant made the need to increase booster coverage in the population even more urgent. OBJECTIVES: to present, using real data, an evaluation of the effectiveness of the booster dose in reducing severe disease caused by SARS-CoV-2 infection in terms of COVID-19 hospitalization and intensive care admission, and all-cause mortality. DESIGN: descriptive study of vaccination uptake;associative study of the factors linked with uptake of vaccination and COVID-19 symptoms;associative study of vaccine effectiveness against hospital admission and mortality. SETTING AND PARTICIPANTS: population residing in the Milan and Lodi provinces (Lombardy Region, Northern Italy), eligible for anti-SARS-COV-2 vaccination, with subjects aged >= 19 years alive as at 01.10.2021, not residing in nursing homes, followed-up until 31.12.2021. MAIN OUTCOME MEASURES: COVID-19 symptoms, hospitalization, intensive care hospitalization, and all-cause mortality in the period 01.10.2021-31.12.2021. RESULTS: the cohort included 2,936,193 patients as of 01.10.2021;at the end of the observation period (31.12.2021), 378,616 (12.9%) were unvaccinated, 60,102 (2.0%) had received only 1 dose and had not had the disease, 68,777 (2.3%) had received only 1 dose and had had the disease, 412,227 (14.0%) were fully vaccinated with 2 doses less than 4 months earlier, 198,459 (6.8%) had received 2 doses [4,5) months earlier, 439,363 (15.0%) had received 2 doses [5,6) months earlier, 87,984 (3.0%) had received 2 doses [6,7) months earlier, 74,152 (2.5%) had received 2 doses more than 7 months earlier, 62,614 (2.1%) had received 2 doses and had had the disease, and, finally, 1,153,899 (39.3%) had received a booster shot. In the study period (01.10.2021-31.12.2021), characterized by a very high prevalence of the omicron variant, 121,620 cases (positive antigen/molecular test), 3,661 hospitalizations for COVID-19, 162 intensive care admissions for COVID-19, and 7,508 deaths from all causes were identified. Compared to unvaccinated subjects, subjects who received a booster had half the risk of being symptomatic, and had half the risk of experiencing fatigue, muscle aches, and dyspnoea. In comparison with boosted subjects, unvaccinated subjects had a 10-fold risk of hospitalization, a 9-fold risk of intensive care, and a 3-fold risk of dying. CONCLUSIONS: this work highlights the effectiveness of vaccination in reducing serious adverse events in boosted subjects and the need to implement specific policies of engagement to bring subjects who received their second dose earliest to get a booster.

Boosters and time from the last anti-COVID-19 vaccine dose: lead public health choices by real-time epidemiological assessment.

BACKGROUND: the levels of anti-SARS-CoV-2 antibodies after the second vaccine dose decline in the following months; the administration of an additional vaccine dose (booster) is able to restore the immune system in the short period significantly reducing the risk of a severe disease. In the winter of 2021, a new particularly infectious variant caused the urgent need to increase the coverage of the booster dose. OBJECTIVES: to present, using real data, an evaluation of the efficacy of the booster dose in reducing the severe disease of SARS-CoV-2 infection in terms of hospital admissions, intensive care and death from all causes. DESIGN: descriptive study of vaccine adherence; associative study of the factors linked with adherence of vaccination and COVID-19 symptoms; associative study of vaccine effectiveness against hospital admission and mortality. SETTING AND PARTICIPANTS: population-based study in the Milan and Lodi provinces (Lombardy Region, Northern Italy) with subjects aged >=19 years alive at 01.10.2021, not residing in a nursery home, followed up to 31.12.2021. MAIN OUTCOME MEASURES: COVID-19 symptoms, hospitalization for COVID-19, intensive care hospitalization, and all-cause mortality in the period 01.10.2021-31.12.2021. RESULTS: the cohort included 2,936,193 patients at 01.10.2021: at the end of the follow-up period (31.12.2021), 378,616 (12.9%) had no vaccine, 128,879 (4.3%) had only 1 dose, 412,227 (14.0%) had a 2nd dose given since less than 4 months, 725. 806 (25%) had a 2nd dose given since 4-7 months, 74,152 (2.5%) had a 2nd dose given since 7+ months, 62,614 (2.1%) had a 2nd dose and have had the disease, and 1,153,899 (39.3%) received the booster. In the study period (01.10.2021-31.12.2021), characterized by a very high prevalence of the omicron variant, 121,620 cases (antigenic/molecular buffer positive), 3,661 hospitalizations for COVID-19, 162 ICU hospitalizations, and 7,508 deaths from all causes were identified. Compared to unvaccinated people, subjects who had the booster dose had half the risk of being symptomatic, in particular for asthenia, muscle pain, and dyspnoea which are the most commons COVID-19 symptoms. In comparison with the subjects who had the booster dose, the unvaccinated had a 10-fold risk of hospitalization for COVID-19, a 9-fold risk of intensive care, and a 3-fold risk of dying. CONCLUSIONS: this work highlights the vaccination efficacy in reducing serious adverse events for those who undergo the booster and the need to implement specific engagement policies to bring to a booster those who had taken the second dose since the longest time.

Evaluation of the anti-COVID-19 vaccination campaign in the Metropolitan Area of Milan (Lombardy Region, Northern Italy).

OBJECTIVES: to present an evaluation of the campaign for vaccination against COVID-19 in the territory covered by the Agency for Health Protection of the Metropolitan Area of Milan from 01.01.2021 to 30.09.2021. DESIGN: descriptive study of vaccine adherence; predictive study of the factors associated with vaccine adherence, efficacy of vaccination in terms of hospitalization and mortality, and factors that increase the risk of hospital admission following full vaccination. SETTING AND PARTICIPANTS: population-based study with subjects aged >18 years eligible for vaccination (N. 2,981,997). An information system obtained by integrating various administrative healthcare sources made it possible to analyse socioeconomic characteristics, COVID-19 related hospitalizations, and general mortality in subjects eligible for vaccination. MAIN OUTCOME MEASURES: full vaccination (2 doses); COVID-19-related hospitalizations, COVID-19-related hospitalizations occurring more than 15 days after the second dose, general mortality. RESULTS: in the first nine months of the vaccination campaign, 74.7% of the subjects (N. 2,228,915) was fully vaccinated, whereas 15.6% (N. 465,829) did not even receive one dose. Women have a lower probability of getting vaccinated than men; the 50-59 years and 70+ years age groups emerge as the most problematic to reach, while the younger one (<40) is the most adherent. A social gradient emerged, with residents of more disadvantaged areas progressively less incline to get vaccinated than those living in more affluent areas. Adherence is greater in Italian citizenship and is likely to increase with an increase in the number of chronic conditions. Hospitalizations amounted to 1.22% (N. 5,672) in the unvaccinated population compared to 0.05% (N. 1,013) in the vaccinated population; general mortality was 4.51% (N. 15,198) in the unvaccinated population against 0.32% (N. 8.733) in the vaccinated population. Sociodemographic factors and the presence of previous health conditions are important predictors of hospitalization outcomes even within the fully vaccinated population. Specifically, the highest hazard ratios are found in subjects with heart failure (HR 2.15; 95%CI 1.83-2.53), in immunocompromised patients (HR 2.02; 95%CI 1.52-2.69), and in transplant recipients (HR 1.92; 95%CI 1.10-3.33). CONCLUSIONS: vaccination campaign adherence is affected by the sociodemographic characteristics of the population and is a determining factor in preventing hospitalizations for COVID-19 and death. The persistent higher risk of hospitalization in chronic subjects following the second dose emphasizes the need to direct booster doses to the more vulnerable. Information systems proved to be effective monitoring tools in the absence of specific trials.