Implementation of AZD7442 (Tixagevimab/Cilgavimab) COVID-19 Pre-exposure Prophylaxis (PrEP) in the Largest Health Maintenance Organization in Israel: Real-world Uptake and Sociodemographic and Clinical Characteristics Across Immunocompromised Patient Groups.

INTRODUCTION: AZD7442 is a combination of two neutralizing antibodies (tixagevimab/cilgavimab) with demonstrated efficacy in reducing the risk of symptomatic coronavirus disease 2019 (COVID-19) among individuals at high risk of severe COVID-19 ≤ 6 months after administration. On February 15, 2022, the Israeli Ministry of Health (IMoH) authorized the administration of 300 mg AZD7442 as pre-exposure prophylaxis (PrEP) against severe acute respiratory syndrome coronavirus 2 infection among immunocompromised individuals aged ≥ 12 years. This study describes the real-world uptake of AZD7442 in Israel. METHODS: This descriptive, observational study analyzed data from Israel's largest health maintenance organization, Clalit Health Services (CHS). Individuals were assessed for AZD7442 eligibility between February 13 and December 11, 2022, and were included if they were aged ≥ 12 years, had ≥ 1 year of continuous CHS membership, had ≥ 1 moderate or severe immunocompromising condition, and were eligible for AZD7442 per IMoH recommendations during this time frame. RESULTS: Overall, 19,161 AZD7442-eligible individuals with immunocompromising conditions were identified during the study period; 2829 (14.8%) received AZD7442. A higher proportion of individuals receiving AZD7442 were older (aged ≥ 65 years), male, not current smokers and residents in large cities; required more physician visits (> 50 visits); and had ≥ 1 COVID-19 hospitalization over 12 months, while uptake was lowest among ultra-orthodox Jewish individuals. AZD7442 uptake was also higher among individuals with multiple comorbidities (Charlson Comorbidity Index ≥ 5), including hypertension, diabetes and chronic kidney disease. In specific immunocompromised types, AZD7442 uptake was highest among individuals with lung transplantation (41%), primary immunodeficiency (32%), bone marrow transplantation (29%) and multiple myeloma (25%) or those receiving anti-CD20 therapy (26%) and was lowest in individuals with lymphoma (8%). CONCLUSION: These results show AZD7442 uptake among the eligible population of Israel in 2022 was relatively low, at 14.8%. Uptake was generally higher among immunocompromised individuals who may be perceived to be frail or at highest risk of COVID-19 infection and complications, although at 25-41%, further improvements in uptake would be more impactful. These results also indicate there is opportunity to expand AZD7442 uptake across immunocompromised groups and ensure more equitable uptake among some other sociodemographic groups. Overall, this study will help inform and reassess future implementation strategies for vulnerable populations.

Adoption and utilization of device-assisted telemedicine.

We estimate the effect of adopting a digital device for performing medical exams at home during telehealth visits. We match visits of adopters and non-adopters who used the same virtual care clinic but without the device and compare healthcare utilization after the matched visits. We find that device adoption, partially offset by decreased use of other primary care modalities, results in a 12% higher utilization rate of primary care and increased use of antibiotics. But - particularly among adults - adoption lowers the use of urgent care, the emergency room, and hospital care, resulting in no increase in total cost.

The role of models in the covid-19 pandemic.

Mathematical and statistical models have played an important role in the analysis of data from COVID-19. They are important for tracking the progress of the pandemic, for understanding its spread in the population, and perhaps most significantly for forecasting the future course of the pandemic and evaluating potential policy options. This article describes the types of models that were used by research teams in Israel, presents their assumptions and basic elements, and illustrates how they were used, and how they influenced decisions. The article grew out of a "modelists' dialog" organized by the Israel National Institute for Health Policy Research with participation from some of the leaders in the local modeling effort.

BNT162b2 vaccine effectiveness in chronic kidney disease patients-an observational study.

Background: Chronic kidney disease (CKD) is a risk factor for severe coronavirus disease 2019 (COVID-19). We aimed to evaluate the real-life effectiveness of the BNT162b2 messenger RNA vaccine for a range of outcomes in patients with CKD compared with matched controls. Methods: Data from Israel's largest healthcare organization were retrospectively used. Vaccinated CKD [estimated glomerular filtration rate (eGFR) <60 ml/min/1.73 m2] and maintenance dialysis patients were matched to vaccinated controls without CKD (eGFR ≥60 ml/min/1.73 m2) according to demographic and clinical characteristics. Study outcomes included documented infection with severe acute respiratory syndrome coronavirus 2, symptomatic infection, COVID-19-related hospitalization, severe disease and death. Vaccine effectiveness was estimated as the risk ratio (RR) at days 7-28 following the second vaccine dose, using the Kaplan-Meier estimator. Effectiveness measures were also evaluated separately for various stages of CKD. Results: There were 67 861 CKD patients not treated with dialysis, 2606 hemodialysis (HD) patients and 70 467 matched controls. The risk of severe disease {RR 1.84 [95% confidence interval (CI) 0.95-2.67]} and death [RR 2.00 (95% CI 0.99-5.20)] was increased in nondialysis CKD patients compared with controls without CKD following vaccination. For the subgroup of patients with eGFR <30 ml/min/1.73 m2, the risk of severe disease and death was increased compared with controls [RR 6.42 (95% CI 1.85-17.51) and RR 8.81 (95% CI 1.63-13.81), respectively]. The risks for all study outcomes were increased in HD patients compared with controls. Conclusion: Two doses of the BNT162b2 vaccine were found to be less efficient for patients with eGFR <30 ml/min/1.73 m2. Risk in HD patients is increased for all outcomes. These results suggest prioritizing patients with eGFR <30 ml/min/1.73 m2 for booster shots, pre- and post-exposure prophylaxis and early COVID-19 therapy.

Effectiveness of REGEN-COV antibody combination in preventing severe COVID-19 outcomes.

REGEN-COV, a combination of the monoclonal antibodies casirivimab and imdevimab, has been approved as a treatment for high-risk patients infected with SARS-CoV-2 within five days of their diagnosis. We performed a retrospective cohort study, and used data repositories of Israel's largest healthcare organization to determine the real-world effectiveness of REGEN-COV treatment against COVID-19-related hospitalization, severe disease, and death. We compared patients infected with Delta variant and treated with REGEN-COV (n = 289) to those infected but not-treated with REGEN-COV (n = 1,296). Demographic and clinical characteristics were used to match patients and for further adjustment as part of the C0x model. Estimated treatment effectiveness was defined as one minus the hazard ratio. Treatment effectiveness of REGEN-COV was 56.4% (95% CI: 23.7-75.1%) in preventing COVID-19 hospitalization, 59.2% (95% CI: 19.9-79.2%) in preventing severe COVID-19, and 93.5% (95% CI: 52.1-99.1%) in preventing COVID-19 death in the 28 days after treatment. In conclusion, REGEN-COV was effective in reducing the risk of severe sequelae in high-risk COVID-19 patients.

BNT162b2 Vaccine Effectiveness against Omicron in Children 5 to 11 Years of Age.

BACKGROUND: Limited evidence is available on the real-world effectiveness of the BNT162b2 vaccine against coronavirus disease 2019 (Covid-19) and specifically against infection with the omicron variant among children 5 to 11 years of age. METHODS: Using data from the largest health care organization in Israel, we identified a cohort of children 5 to 11 years of age who were vaccinated on or after November 23, 2021, and matched them with unvaccinated controls to estimate the vaccine effectiveness of BNT162b2 among newly vaccinated children during the omicron wave. Vaccine effectiveness against documented severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and symptomatic Covid-19 was estimated after the first and second vaccine doses. The cumulative incidence of each outcome in the two study groups through January 7, 2022, was estimated with the use of the Kaplan-Meier estimator, and vaccine effectiveness was calculated as 1 minus the risk ratio. Vaccine effectiveness was also estimated in age subgroups. RESULTS: Among 136,127 eligible children who had been vaccinated during the study period, 94,728 were matched with unvaccinated controls. The estimated vaccine effectiveness against documented infection was 17% (95% confidence interval [CI], 7 to 25) at 14 to 27 days after the first dose and 51% (95% CI, 39 to 61) at 7 to 21 days after the second dose. The absolute risk difference between the study groups at days 7 to 21 after the second dose was 1905 events per 100,000 persons (95% CI, 1294 to 2440) for documented infection and 599 events per 100,000 persons (95% CI, 296 to 897) for symptomatic Covid-19. The estimated vaccine effectiveness against symptomatic Covid-19 was 18% (95% CI, -2 to 34) at 14 to 27 days after the first dose and 48% (95% CI, 29 to 63) at 7 to 21 days after the second dose. We observed a trend toward higher vaccine effectiveness in the youngest age group (5 or 6 years of age) than in the oldest age group (10 or 11 years of age). CONCLUSIONS: Our findings suggest that as omicron was becoming the dominant variant, two doses of the BNT162b2 messenger RNA vaccine provided moderate protection against documented SARS-CoV-2 infection and symptomatic Covid-19 in children 5 to 11 years of age. (Funded by the European Union through the VERDI project and others.).

Comparing COVID-19-related hospitalization rates among individuals with infection-induced and vaccine-induced immunity in Israel.

With the COVID-19 pandemic ongoing, accurate assessment of population immunity and the effectiveness of booster and enhancer vaccine doses is critical. We compare COVID-19-related hospitalization incidence rates in 2,412,755 individuals across four exposure levels: non-recent vaccine immunity (two BNT162b2 COVID-19 vaccine doses five or more months prior), boosted vaccine immunity (three BNT162b2 doses), infection-induced immunity (previous COVID-19 without a subsequent BNT162b2 dose), and enhanced infection-induced immunity (previous COVID-19 with a subsequent BNT162b2 dose). Rates, adjusted for potential demographic, clinical and health-seeking-behavior confounders, were assessed from July-November 2021 when the Delta variant was predominant. Compared with non-recent vaccine immunity, COVID-19-related hospitalization incidence rates were reduced by 89% (87-91%) for boosted vaccine immunity, 66% (50-77%) for infection-induced immunity and 75% (61-83%) for enhanced infection-induced immunity. We demonstrate that infection-induced immunity (enhanced or not) provides more protection against COVID-19-related hospitalization than non-recent vaccine immunity, but less protection than booster vaccination. Additionally, our results suggest that vaccinating individuals with infection-induced immunity further enhances their protection.

Fourth Dose of BNT162b2 mRNA Covid-19 Vaccine in a Nationwide Setting.

BACKGROUND: With large waves of infection driven by the B.1.1.529 (omicron) variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), alongside evidence of waning immunity after the booster dose of coronavirus disease 2019 (Covid-19) vaccine, several countries have begun giving at-risk persons a fourth vaccine dose. METHODS: To evaluate the early effectiveness of a fourth dose of the BNT162b2 vaccine for the prevention of Covid-19-related outcomes, we analyzed data recorded by the largest health care organization in Israel from January 3 to February 18, 2022. We evaluated the relative effectiveness of a fourth vaccine dose as compared with that of a third dose given at least 4 months earlier among persons 60 years of age or older. We compared outcomes in persons who had received a fourth dose with those in persons who had not, individually matching persons from these two groups with respect to multiple sociodemographic and clinical variables. A sensitivity analysis was performed with the use of parametric Poisson regression. RESULTS: The primary analysis included 182,122 matched pairs. Relative vaccine effectiveness in days 7 to 30 after the fourth dose was estimated to be 45% (95% confidence interval [CI], 44 to 47) against polymerase-chain-reaction-confirmed SARS-CoV-2 infection, 55% (95% CI, 53 to 58) against symptomatic Covid-19, 68% (95% CI, 59 to 74) against Covid-19-related hospitalization, 62% (95% CI, 50 to 74) against severe Covid-19, and 74% (95% CI, 50 to 90) against Covid-19-related death. The corresponding estimates in days 14 to 30 after the fourth dose were 52% (95% CI, 49 to 54), 61% (95% CI, 58 to 64), 72% (95% CI, 63 to 79), 64% (95% CI, 48 to 77), and 76% (95% CI, 48 to 91). In days 7 to 30 after a fourth vaccine dose, the difference in the absolute risk (three doses vs. four doses) was 180.1 cases per 100,000 persons (95% CI, 142.8 to 211.9) for Covid-19-related hospitalization and 68.8 cases per 100,000 persons (95% CI, 48.5 to 91.9) for severe Covid-19. In sensitivity analyses, estimates of relative effectiveness against documented infection were similar to those in the primary analysis. CONCLUSIONS: A fourth dose of the BNT162b2 vaccine was effective in reducing the short-term risk of Covid-19-related outcomes among persons who had received a third dose at least 4 months earlier. (Funded by the Ivan and Francesca Berkowitz Family Living Laboratory Collaboration at Harvard Medical School and Clalit Research Institute.).

Pre- and Perinatal Factors Predicting Inflammatory Bowel Disease: A Population-Based Study with Fifty Years of Follow-Up.

BACKGROUND: Pre- and perinatal events may be associated with an increased risk of inflammatory bowel disease [IBD]. We aimed to investigate the role of pre- and perinatal factors as potential risk factors for the development of IBD in a population with a follow-up of 50 years. METHODS: We conducted a nested case-control study, reporting IBD incidence among individuals born in 1964-76, for whom pre- and perinatal exposures were reported as part of the Jerusalem Perinatal Study [JPS], by linking them to the database of the epidemiology group of the Israeli IBD Research Nucleus [epi-IIRN], including all IBD patients in Israel since 2005 and their matched controls. RESULTS: We identified 2789 individuals within the epi-IIRN cohort who were also included in the JPS cohort [n = 90 079]: 746 IBD patients (405 with Crohn's disease [CD] and 341 with ulcerative colitis [UC]) and 2043 non-IBD controls. Those with a 'Non-western' family origin had decreased odds of developing CD and UC. High socioeconomic status was associated with CD but not UC. Low birth weight [≤2500 g] occurred less frequently in IBD cases compared to controls, especially in UC patients, showing a protective effect. Being the first born was associated with CD, and having older siblings lowered the odds of developing CD, decreasing 7% with each additional sibling. Smoking and breastfeeding data were available for a subset of individuals, but neither was associated with IBD development. CONCLUSION: This population-based study identifies several pre- and perinatal variables as predictors of IBD development. This information may be helpful to facilitate implementation of early diagnosis interventions and family follow-up protocols.

Indirect protection of children from SARS-CoV-2 infection through parental vaccination.

Children not vaccinated against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) may still benefit from vaccines through protection from vaccinated contacts. We estimated the protection provided to children through parental vaccination with the BNT162b2 vaccine. We studied households without prior infection consisting of two parents and unvaccinated children, estimating the effect of parental vaccination on the risk of infection for unvaccinated children. We studied two periods separately-an early period (17 January 2021 to 28 March 2021; Alpha variant, two doses versus no vaccination) and a late period (11 July 2021 to 30 September 2021; Delta variant, booster dose versus two vaccine doses). We found that having a single vaccinated parent was associated with a 26.0 and a 20.8% decreased risk in the early and late periods, respectively, and having two vaccinated parents was associated with a 71.7 and a 58.1% decreased risk, respectively. Thus, parental vaccination confers substantial protection on unvaccinated children in the household.

Identification of elderly patients at risk for 30-day readmission: Clinical insight beyond big data prediction.

AIM: This study explores the potential benefit of combining clinicians' risk assessments and the automated 30-day readmission prediction model. BACKGROUND: Automated readmission prediction models based on electronic health records are increasingly applied as part of prevention efforts, but their accuracy is moderate. METHODS: This prospective multisource study was based on self-reported surveys of clinicians and data from electronic health records. The survey was performed at 15 internal medicine wards of three general Clalit hospitals between May 2016 and June 2017. We examined the degree of concordance between the Preadmission Readmission Detection Model, clinicians' readmission risk classification and the likelihood of actual readmission. Decision trees were developed to classify patients by readmission risk. RESULTS: A total of 694 surveys were collected for 371 patients. The disagreement between clinicians' risk assessment and the model was 34.5% for nurses and 33.5% for physicians. The decision tree algorithms identified 22% and 9% (based on nurses and physicians, respectively) of the model's low-medium-risk patients as high risk (accuracy 0.8 and 0.76, respectively). CONCLUSIONS: Combining the Readmission Model with clinical insight improves the ability to identify high-risk elderly patients. IMPLICATIONS FOR NURSING MANAGEMENT: This study provides algorithms for the decision-making process for selecting high-risk readmission patients based on nurses' evaluations.

Mixed Methods Evaluation of Reasons Why Care Deviates From Clinical Guidelines Among Patients With Multimorbidity.

Reasons why care does not conform to single-disease guideline recommendations for multimorbid patients have not been systematically measured in practice. Using a mixed methods approach, we identified and quantified types of reasons why care deviates from nine sets of disease guideline recommendations for multimorbid patients. Utilizing a focus group concept mapping technique, we built on a categorization of reasons explaining guideline deviation, and surveyed treating nurses about these reasons for patients' specific care processes. Directed content analysis was conducted to classify the responses into reasons categories. Of 4,386 guideline-recommended care processes evaluated, 920 were not guideline-concordant (944 reasons). Three broad categories of reasons and 18 specific reasons were identified: Biomedical-related occurred 35.2% of the time, patient personal-related (30.4%), context-related (18.4%), and unknown (16.0%). Patient- and context-related factors are prevalent drivers for guideline deviation in multimorbidity, demonstrating that patient-centered aspects are as much a part of care decisions as biomedical aspects.

Using population-level incidence of hepatitis C virus and immigration status for data-driven screening policies: a case study in Israel.

BACKGROUND: Most studies estimate hepatitis C virus (HCV) disease prevalence from convenience samples. Consequently, screening policies may not include those at the highest risk for a new diagnosis. METHODS: Clalit Health Services members aged 25-74 as of 31 December 2009 were included in the study. Rates of testing and new diagnoses of HCV were calculated, and potential risk groups were examined. RESULTS: Of the 2 029 501 included members, those aged 45-54 and immigrants had lower rates of testing (12.5% and 15.6%, respectively), higher rates of testing positive (0.8% and 1.1%, respectively), as well as the highest rates of testing positive among tested (6.1% and 6.9%, respectively). DISCUSSION: In this population-level study, groups more likely to test positive for HCV also had lower rates of testing. Policy makers and clinicians worldwide should consider creating screening policies using on population-based data to maximize the ability to detect and treat incident cases.

Early effectiveness of BNT162b2 Covid-19 vaccine in preventing SARS-CoV-2 infection in healthcare personnel in six Israeli hospitals (CoVEHPI).

BACKGROUND: Methodologically rigorous studies on Covid-19 vaccine effectiveness (VE) in preventing SARS-CoV-2 infection are critically needed to inform national and global policy on Covid-19 vaccine use. In Israel, healthcare personnel (HCP) were initially prioritized for Covid-19 vaccination, creating an ideal setting to evaluate early real-world VE in a closely monitored population. METHODS: We conducted a prospective study among HCP in 6 hospitals to estimate the effectiveness of the BNT162b2 mRNA Covid-19 vaccine in preventing SARS-CoV-2 infection. Participants filled out weekly symptom questionnaires, provided weekly nasal specimens, and three serology samples - at enrollment, 30 days and 90 days. We estimated VE against PCR-confirmed SARS-CoV-2 infection using the Cox Proportional Hazards model and against a combined PCR/serology endpoint using Fisher's exact test. RESULTS: Of the 1567 HCP enrolled between December 27, 2020 and February 15, 2021, 1250 previously uninfected participants were included in the primary analysis; 998 (79.8%) were vaccinated with their first dose prior to or at enrollment, all with Pfizer BNT162b2 mRNA vaccine. There were four PCR-positive events among vaccinated participants, and nine among unvaccinated participants. Adjusted two-dose VE against any PCR-confirmed infection was 94.5% (95% CI: 82.6%-98.2%); adjusted two-dose VE against a combined endpoint of PCR and seroconversion for a 60-day follow-up period was 94.5% (95% CI: 63.0%-99.0%). Five PCR-positive samples from study participants were sequenced; all were alpha variant. CONCLUSIONS: Our prospective VE study of HCP in Israel with rigorous weekly surveillance found very high VE for two doses of Pfizer BNT162b2 mRNA vaccine against SARS-CoV-2 infection in recently vaccinated HCP during a period of predominant alpha variant circulation. FUNDING: Clalit Health Services.

SARS-CoV-2 breakthrough infections in vaccinated individuals: measurement, causes and impact.

Breakthrough infections with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in fully vaccinated individuals are receiving intense scrutiny because of their importance in determining how long restrictions to control virus transmission will need to remain in place in highly vaccinated populations as well as in determining the need for additional vaccine doses or changes to the vaccine formulations and/or dosing intervals. Measurement of breakthrough infections is challenging outside of randomized, placebo-controlled, double-blind field trials. However, laboratory and observational studies are necessary to understand the impact of waning immunity, viral variants and other determinants of changing vaccine effectiveness against various levels of coronavirus disease 2019 (COVID-19) severity. Here, we describe the approaches being used to measure vaccine effectiveness and provide a synthesis of the burgeoning literature on the determinants of vaccine effectiveness and breakthrough rates. We argue that, rather than trying to tease apart the contributions of factors such as age, viral variants and time since vaccination, the rates of breakthrough infection are best seen as a consequence of the level of immunity at any moment in an individual, the variant to which that individual is exposed and the severity of disease being considered. We also address key open questions concerning the transition to endemicity, the potential need for altered vaccine formulations to track viral variants, the need to identify immune correlates of protection, and the public health challenges of using various tools to counter breakthrough infections, including boosters in an era of global vaccine shortages.

Effectiveness of a third dose of the BNT162b2 mRNA COVID-19 vaccine for preventing severe outcomes in Israel: an observational study.

BACKGROUND: Many countries are experiencing a resurgence of COVID-19, driven predominantly by the delta (B.1.617.2) variant of SARS-CoV-2. In response, these countries are considering the administration of a third dose of mRNA COVID-19 vaccine as a booster dose to address potential waning immunity over time and reduced effectiveness against the delta variant. We aimed to use the data repositories of Israel's largest health-care organisation to evaluate the effectiveness of a third dose of the BNT162b2 mRNA vaccine for preventing severe COVID-19 outcomes. METHODS: Using data from Clalit Health Services, which provides mandatory health-care coverage for over half of the Israeli population, individuals receiving a third vaccine dose between July 30, 2020, and Sept 23, 2021, were matched (1:1) to demographically and clinically similar controls who did not receive a third dose. Eligible participants had received the second vaccine dose at least 5 months before the recruitment date, had no previous documented SARS-CoV-2 infection, and had no contact with the health-care system in the 3 days before recruitment. Individuals who are health-care workers, live in long-term care facilities, or are medically confined to their homes were excluded. Primary outcomes were COVID-19-related admission to hospital, severe disease, and COVID-19-related death. The third dose effectiveness for each outcome was estimated as 1 - risk ratio using the Kaplan-Meier estimator. FINDINGS: 1 158 269 individuals were eligible to be included in the third dose group. Following matching, the third dose and control groups each included 728 321 individuals. Participants had a median age of 52 years (IQR 37-68) and 51% were female. The median follow-up time was 13 days (IQR 6-21) in both groups. Vaccine effectiveness evaluated at least 7 days after receipt of the third dose, compared with receiving only two doses at least 5 months ago, was estimated to be 93% (231 events for two doses vs 29 events for three doses; 95% CI 88-97) for admission to hospital, 92% (157 vs 17 events; 82-97) for severe disease, and 81% (44 vs seven events; 59-97) for COVID-19-related death. INTERPRETATION: Our findings suggest that a third dose of the BNT162b2 mRNA vaccine is effective in protecting individuals against severe COVID-19-related outcomes, compared with receiving only two doses at least 5 months ago. FUNDING: The Ivan and Francesca Berkowitz Family Living Laboratory Collaboration at Harvard Medical School and Clalit Research Institute.

Myocarditis after Covid-19 Vaccination in a Large Health Care Organization.

BACKGROUND: Reports have suggested an association between the development of myocarditis and the receipt of messenger RNA (mRNA) vaccines against coronavirus disease 2019 (Covid-19), but the frequency and severity of myocarditis after vaccination have not been extensively explored. METHODS: We searched the database of Clalit Health Services, the largest health care organization (HCO) in Israel, for diagnoses of myocarditis in patients who had received at least one dose of the BNT162b2 mRNA vaccine (Pfizer-BioNTech). The diagnosis of myocarditis was adjudicated by cardiologists using the case definition used by the Centers for Disease Control and Prevention. We abstracted the presentation, clinical course, and outcome from the patient's electronic health record. We performed a Kaplan-Meier analysis of the incidence of myocarditis up to 42 days after the first vaccine dose. RESULTS: Among more than 2.5 million vaccinated HCO members who were 16 years of age or older, 54 cases met the criteria for myocarditis. The estimated incidence per 100,000 persons who had received at least one dose of vaccine was 2.13 cases (95% confidence interval [CI], 1.56 to 2.70). The highest incidence of myocarditis (10.69 cases per 100,000 persons; 95% CI, 6.93 to 14.46) was reported in male patients between the ages of 16 and 29 years. A total of 76% of cases of myocarditis were described as mild and 22% as intermediate; 1 case was associated with cardiogenic shock. After a median follow-up of 83 days after the onset of myocarditis, 1 patient had been readmitted to the hospital, and 1 had died of an unknown cause after discharge. Of 14 patients who had left ventricular dysfunction on echocardiography during admission, 10 still had such dysfunction at the time of hospital discharge. Of these patients, 5 underwent subsequent testing that revealed normal heart function. CONCLUSIONS: Among patients in a large Israeli health care system who had received at least one dose of the BNT162b2 mRNA vaccine, the estimated incidence of myocarditis was 2.13 cases per 100,000 persons; the highest incidence was among male patients between the ages of 16 and 29 years. Most cases of myocarditis were mild or moderate in severity. (Funded by the Ivan and Francesca Berkowitz Family Living Laboratory Collaboration at Harvard Medical School and Clalit Research Institute.).