Saad B Omer

• MBBS, MPH, PhD
• Director at Yale University

Involvement of women is critical in establishing guidelines

The continued success of vaccines, one of the most effective public health interventions, depends on high rates of acceptance. Vaccine refusal in the United States has increased since the late 1990s.¹ This trend has coincided with an increase in vaccine safety concerns. Such concerns result from easy recall of adverse events, misinformation, and hu...

Background: Vaccination coverage with tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis (Tdap) vaccine in pregnancy or immediately postpartum has been low. Limited data exist on rigorously evaluated interventions to increase maternal vaccination, including Tdap. Tailored messaging based on the Elaboration Likelihood Model (ELM) fr...

Infants can be protected against a variety of dangerous infections early in life through immunity transferred from their mothers. This article reviews the efficacy of maternal immunization in the prevention of infections in babies too young to be immunized directly.

Despite high measles vaccination rates in the United States, imported measles cases have led to outbreaks in the United States. These outbreaks have not led to sustained measles transmission; however, with each birth cohort of children not fully vaccinated against measles, measles-susceptible individuals accumulate in the population. The total numb...

Misinformation about COVID-19 vaccines has hampered their uptake worldwide. In Ghana, a belief that COVID-19 vaccines affect fertility is prevalent and difficult to counter. UNICEF Ghana co-produced a context-driven, behavioral science-based audio drama (‘A shot of love’) that aimed to debunk this misinformation narrative. In a randomized controlle...

Background Mozambique introduced 10-valent-pneumococcal conjugate vaccine (PCV10) in 2013. We aimed to evaluate the indirect effect of PCV10 on invasive pneumococcal disease (IPD) and clinical severe pneumonia (CSP) in infants aged less than 10 weeks. Methods Routine surveillance data for IPD and CSP among admitted infants less than 10 weeks of ag...

Background Tuberculosis (TB) disease during pregnancy results in adverse maternal and infant outcomes. The development of a TB vaccine with potential for administration during pregnancy or lactation is a priority identified by the World Health Organization. We assessed the acceptability of vaccines currently administered during pregnancy [tetanus,...

Background Understanding healthcare personnel’s (HCP) contact patterns are important to mitigate healthcare-associated infectious disease transmission. Little is known about how HCP contact patterns change over time or during outbreaks such as the COVID-19 pandemic. Methods This study in a large United States healthcare system examined the social...

Background Since February 2022, millions of Ukrainian women and children have fled their home country. Evidence suggests that vaccination coverage among Ukrainian refugee children is sub-optimal. We therefore tested the effect of three messages on mothers’ intention to vaccinate their children, and on scheduling a vaccination appointment. Methods...

Background We lack understanding of how health care workers’ (HCWs) contacts change over time or in response to pandemics. This study describes the social contact patterns of HCWs in a large United States health care system via standardized social contact diaries. Mean number of total contacts over time (Jan 2021-May 2022): The mean contacts noted...

Few sources have reported empirical social contact data from resource-poor settings. To address this shortfall, we recruited 1,363 participants from rural and urban areas of Mozambique during the COVID-19 pandemic, determining age, sex, and relation to the contact for each person. Participants reported a mean of 8.3 (95% CI 8.0-8.6) contacts per pe...

The uptake of routine childhood vaccinations has declined globally since the start of the COVID-19 pandemic, due in part to increased vaccine hesitancy among parents. The Moral Foundations Theory proposes six foundations which can be targeted to increase vaccine uptake. In this study, we tested whether a post by UNICEF with a purity violation messa...

Background Since February 2022, the start of the full-scale war in Ukraine, millions of women and children have fled the country. Vaccination of refugee children is important to protect this vulnerable population from disease. Aim We investigate the determinants of vaccination intention in refugee mothers from Ukraine residing in Poland and test t...

Background Low-and-middle-income countries (LMICs) bear a disproportionate burden of communicable diseases. Social interaction data inform infectious disease models and disease prevention strategies. The variations in demographics and contact patterns across ages, cultures, and locations significantly impact infectious disease dynamics and pathogen...

Introduction There are few sources of empirical social contact data from resource-poor settings thus limiting the development of contextual mathematical models of disease transmission and control. Methods We collected and analyzed cross-sectional survey data from rural and urban sites in Mozambique. Participants, including infants, were recruited....

Immunological memory mediates rapid protection following infection or vaccination including heterologous exposure. However, cross-reactive memory responses in humans remain poorly characterized. We explored the longevity and specificity of cross-protective responses to orthopoxviruses through smallpox vaccination and Mpox virus (MPXV) infection. Sm...

Immunological memory mediates rapid protection following infection or vaccination including heterologous exposure. However, cross-reactive memory responses in humans remain poorly characterized. We explored the longevity and specificity of cross-protective responses to orthopoxviruses through smallpox vaccination and Mpox virus (MPXV) infection. Sm...

Background Minimally invasive tissue sampling (MITS) has increasingly been used to improve the diagnosis of disease and identification of the cause of death, particularly in underserved areas. However, there are multiple barriers to accessing those who die within the community, our study aimed to explore the perceptions and insights of community me...

Background When a randomized controlled trial fails to demonstrate statistically significant efficacy against the primary endpoint, a potentially costly new trial would need to be conducted to receive licensure. Incorporating data from previous trials might allow for more efficient follow-up trials to demonstrate efficacy, speeding availability of...

Non-pharmaceutical interventions minimize social contacts, hence the spread of respiratory pathogens such as influenza and SARS-CoV-2. Globally, there is a paucity of social contact data from the workforce. In this study, we quantified two-day contact patterns among USA employees. Contacts were defined as face-to-face conversations, involving physi...

Objective We measured contact patterns using social contact diaries for 157 U.S. long-term care facility employees from December 2020 - June 2021. These data are crucial for analyzing mathematical transmission models and for informing healthcare setting infection control policy. Results The median number of daily contacts was 10 (IQR 8–11). Househ...

The COVID-19 pandemic has added new urgency to the question of how best to motivate people to get needed vaccines. In this article, we present lessons gleaned from government evaluations of eight large randomized controlled trials of interventions that used direct communications to increase the uptake of routine vaccines. These evaluations, conduct...

This study evaluates changes in medical exemptions and geographic distribution of kindergarteners in California not up to date on vaccination after changes to state legislation.

Background Wastewater-based surveillance is used to track the temporal patterns of the SARS-CoV-2 virus in communities. Viral RNA particle detection in wastewater samples can indicate an outbreak within a catchment area. We describe the feasibility of using a sewage network to monitor SARS-CoV-2 trend and use of genomic sequencing to describe the v...

Social media platforms have a wide and influential reach, and as such provide an opportunity to increase vaccine uptake. To date, there is no large-scale, robust evidence on the offline effects of online messaging campaigns. We aimed to test whether pre-tested, persuasive messaging campaigns from UNICEF, disseminated on Facebook, influenced COVID-1...

Post-acute infection syndromes may develop after acute viral disease ¹ . Infection with SARS-CoV-2 can result in the development of a post-acute infection syndrome known as long COVID. Individuals with long COVID frequently report unremitting fatigue, post-exertional malaise, and a variety of cognitive and autonomic dysfunctions 2–4 . However, the...

Objective To determine the association of Nirmatlevir/ritonavir (NMV/r) with hospitalization or death within 30 days compared with untreated controls in previously uninfected non-hospitalized persons. Methods We used a matched cohort design using inverse probability of treatment weights (IPTW). Individuals prescribed NMV/r within 3 days of COVID-1...

Seroprevalence provides an estimate of the population-level susceptibility to infection. In this study, we used a transmission model to examine the potential of using serological surveillance to inform the timing of COVID-19 boosters in Mozambique. We simulated using population-level seroprevalence thresholds as an estimate of the risk of outbreaks...

Background Human behavior and more specifically behavioral insight-based approaches to vaccine uptake have often been overlooked. While there have been a few narrative reviews indexed in Medline on behavioral interventions to increase vaccine uptake, to our knowledge, none have been systematic reviews and meta-analyses covering not just high but al...

Whether SARS-CoV-2 infection and COVID-19 vaccines confer exposure-dependent (“leaky”) protection against infection remains unknown. We examined the effect of prior infection, vaccination, and hybrid immunity on infection risk among residents of Connecticut correctional facilities during periods of predominant Omicron and Delta transmission. Reside...

Background: Clinical benefit of Molnupiravir (MPV) in COVID-19 infected sub-populations is unclear. Methods: We used a matched cohort study design to determine the rate of hospitalization or death within 30 days of COVID-19 diagnosis among MPV treated and untreated controls. Participants were non-hospitalized, previously uninfected Veterans with...

Rare immune-mediated cardiac tissue inflammation can occur after vaccination, including after SARS-CoV-2 mRNA vaccines. However, the underlying immune cellular and molecular mechanisms driving this pathology remain poorly understood. Here, we investigated a cohort of patients who developed myocarditis and/or pericarditis with elevated troponin, B-t...

Parental hesitancy poses a serious threat to the success of the COVID-19 childhood vaccination campaign. We investigate whether adults' opinions on childhood vaccination can be influenced via two survey experiments in Italy (n = 3,633 participants) and the UK (n = 3,314 participants). Respondents were randomly assigned to: a "risk treatment" that h...

Improved uptake of adult vaccinations could substantially reduce the burden of infectious disease worldwide, however very few countries achieve high coverage of recommended adult vaccinations. Vaccine hesitancy is an important driver of low vaccine uptake among adults but no measure currently exists to capture general vaccination attitudes in this...

Background. When a randomized controlled trial fails to demonstrate statistical efficacy against the primary endpoint, a costly new trial would need to be conducted to receive a license. Partially incorporating data from previous trials might allow for the conduct of a more efficient follow-up trial to demonstrate efficacy, speeding the availabilit...

Developing a timely and effective response to emerging SARS-CoV-2 Variants of Concern (VOCs) is of paramount public health importance. Global health surveillance does not rely on genomic data alone to identify concerning variants when they emerge. Instead, methods that utilise genomic data to estimate the epidemiological dynamics of emerging lineag...

mRNA-based vaccines dramatically reduce the occurrence and severity of COVID-19, but are associated with rare vaccine-related adverse effects. These toxicities, coupled with observations that SARS-CoV-2 infection is associated with autoantibody development, raise questions whether COVID-19 vaccines may also promote the development of autoantibodies...

We examined the effectiveness of maternal vaccination against SARS-CoV-2 infection in 30,311 infants born at Kaiser Permanente Northern California from December 15, 2020, to May 31, 2022. Using Cox regression, the effectiveness of ≥2 doses of COVID-19 vaccine received during pregnancy was 84% (95% confidence interval [CI]: 66, 93), 62% (CI: 39, 77)...

Whether SARS-CoV-2 infection and COVID-19 vaccines confer exposure-dependent ("leaky") protection remains unknown. We examined the effect of prior infection and vaccination on infection risk among residents of Connecticut correctional facilities during periods of predominant Omicron and Delta transmission. Residents with cell, unit, and no document...

The emergence of the SARS-CoV-2 Omicron sublineages resulted in increased transmission rates and reduced protection from vaccines. To counteract these effects, multiple booster strategies were used in different countries, although data comparing their efficiency in improving protective immunity remain sparse, especially among vulnerable populations...

Background Respiratory syncytial virus (RSV) is the most common cause of acute lower respiratory infection in young children. We previously estimated that in 2015, 33·1 million episodes of RSV-associated acute lower respiratory infection occurred in children aged 0-60 months, resulting in a total of 118 200 deaths worldwide. Since then, several com...

Background: Lebanon endured its worst economic and financial crisis in 2020-2021. To minimize the impact of COVID-19 pandemic, it is important to improve the overall COVID-19 vaccination rate. Given that vaccine hesitancy among health care workers (HCWs) affects the general population's decision to be vaccinated, our study assessed COVID-19 vaccin...

Non-pharmaceutical interventions minimize social contacts, hence the spread of SARS-CoV-2. We quantified two-day contact patterns among USA employees from 2020–2021 during the COVID-19 pandemic. Contacts were defined as face-to-face conversations, involving physical touch or proximity to another individual and were collected using electronic diarie...

Background: New data on COVID-19 may influence the stringency of containment policies, but these potential effect are not understood. We aimed to understand the associations of new COVID-19 cases and deaths with policy stringency globally and regionally. Methods: We modelled the marginal effects of new COVID-19 cases and deaths on policy stringe...

Amidst an unprecedented Monkeypox outbreak, we aimed to measure knowledge, attitudes, practices and Monkeypox vaccination intentions among the U.S. adult population. We conducted an online cross-sectional survey, representative of the U.S. adult general public in June 2022. We asked participants whether they would receive a Monkeypox vaccine, if th...

In October 2021, Emergency Use Authorization of Coronavirus Disease 2019 (COVID-19) vaccines was granted for children aged 5-11. To ensure vaccine uptake in children upon approval, California will implement a state-wide executive order mandating COVID-19 vaccination for school children following full US FDA approval. This study uses survey data col...

Background Many pregnant women and parents have concerns about vaccines. This analysis examined the impact of MomsTalkShots, an individually tailored educational application, on vaccine attitudes of pregnant women and mothers. Methods MomsTalkShots was the patient-level component of a multi-level intervention to improve maternal and infant vaccine...

Importance Patients from racially and ethnically minoritized populations, such as Black and Hispanic patients, may be less likely to receive evidence-based COVID-19 treatments than White patients, contributing to adverse clinical outcomes. Objective To determine whether clinical treatments and outcomes among patients hospitalized with COVID-19 wer...

To evaluate the early vaccine landscape relative to challenges faced by low- and middle-income countries (LMIC), we conducted a cross-sectional study of all COVID-19 vaccines in clinical trials in 2021 (n = 123) using a structured 13-point analytic framework. Supply sustainability was defined as a composite metric of four manufacturing and regulati...

Importance All U.S. states provided Covid-19 vaccine access to frontline healthcare workers first, but after that, states varied in whether they gave earlier access to the elderly, versus the vulnerable with comorbidities, or school employees or essential workers, reflecting the underlying scientific and policy uncertainty. Objective To evaluate i...

Background Clinical pediatric TB diagnosis may lead to over-diagnosis particularly among children with HIV (CHIV). We assessed the performance of monocyte-lymphocyte ratio (MLR) as a diagnostic biomarker and constructed a clinical prediction score to improve specificity of TB diagnosis in CHIV with limited access to microbiologic testing. Methods...

We examined the effectiveness of maternal vaccination against SARS-CoV-2 infection in 30,288 infants born at Kaiser Permanente Northern California from December 15, 2020, to May 31, 2022. Using Cox regression, the effectiveness of maternal vaccination was 85% (95% confidence interval [CI]: 67, 93), 64% (CI: 43, 78) and 57% (CI: 36,71) during the fi...

The emergence of the SARS-CoV-2 Omicron sublineages resulted in drastically increased transmission rates and reduced protection from vaccine-induced immunity. To counteract these effects, multiple booster strategies were used in different countries, although data comparing their efficiency in improving protective immunity remains sparse, especially...

Introduction: Given their central role in supporting children's development, childcare professionals' overall physical and mental health is important. We evaluated the prevalence of chronic diseases, depression, and stress levels during the COVID-19 pandemic among US childcare professionals. Methods: Data were obtained from US childcare professi...

Influenza causes significant mortality and morbidity in the United States (US). Employees are exposed to influenza at work and can spread it to others. The influenza vaccine is safe, effective, and prevents severe outcomes; however, coverage among US adults (50.2%) is below Healthy People 2030 target of 70%. These highlights need for more effective...

Background The discovery of vaccines significantly reduced morbidity and mortality of infectious diseases and led to the elimination and eradication of some. Development of safe and effective vaccines is a critical step to the control of infectious diseases; however, there is the need to address vaccine hesitancy because of its potential impact on...

In 2020, 26 million refugees resettled in a new country—fleeing their homes due to conflict and persecution. Due to low immunization coverage and underlying health conditions, refugees commonly face an increased risk of contracting vaccine-preventable diseases. We collected and analyzed existing routine immunization policies for refugees across 20...

SARS-CoV-2 infection can result in the development of a constellation of persistent sequelae following acute disease called post-acute sequelae of COVID-19 (PASC) or Long COVID. Individuals diagnosed with Long COVID frequently report unremitting fatigue, post-exertional malaise, and a variety of cognitive and autonomic dysfunctions; however, the ba...

Faced with the challenge of advising the World Health Organization on who should be the first to receive COVID-19 vaccines, an advisory group used an approach it hadn’t tried before. Faced with the challenge of advising the World Health Organization on who should be the first to receive COVID-19 vaccines, an advisory group used an approach it hadn’...

Objective To understand the associations of COVID-19 cases and deaths with policy stringency globally and regionally. Methods We modeled the marginal effects of new COVID-19 cases and deaths on policy stringency (scored 0–100) in 175 countries and territories, adjusting for gross domestic product (GDP) per capita and health expenditure (% of GDP)....

Objective To evaluate the impact of a multi-component intervention package of maternal immunization uptake in obstetric care clinics. Methods In a multi-level, cluster- and individually-randomized controlled trial we implemented an evidence-based intervention that targeted practice-, provider- and patient-level barriers to vaccine uptake. Obstetri...

The SARS-CoV-2 Omicron variant is thought to cause less severe disease among the general population, but disease severity among at-risk populations is unknown. We performed a retrospective analysis using a matched cohort of United States veterans to compare the disease severity of subjects infected during Omicron and Delta predominant periods withi...

Background Comparative effectiveness of COVID-19 vaccines across patient subgroups is poorly understood and essential to precisely target vaccination strategies. Methods We used the US Department of Veterans Affairs COVID-19 Shared Data Resource to identify veterans who utilize VA healthcare and had no documented SARS-CoV-2 infection before Decemb...

While the Monkeypox outbreak is growing, little is known about the general public’s levels of knowledge, their trusted sources of information and attitudes towards a Monkeypox vaccine. In our representative survey of the US general public, we find that almost half the respondents (47%) feel that their knowledge level about Monkeypox is poor or very...

The impact of Coronavirus Disease 2019 (COVID-19) mRNA vaccination on pregnancy and fertility has become a major topic of public interest. We investigated 2 of the most widely propagated claims to determine (1) whether COVID-19 mRNA vaccination of mice during early pregnancy is associated with an increased incidence of birth defects or growth abnor...

Background Respiratory syncytial virus (RSV) is the most common cause of acute lower respiratory infection in young children. We previously estimated that in 2015, 33·1 million episodes of RSV-associated acute lower respiratory infection occurred in children aged 0-60 months, resulting in a total of 118 200 deaths worldwide. Since then, several com...

Background The current SARS-CoV-2 vaccines may be less effective against the Omicron variant. With recent resurgence of SARS-CoV-2 cases, the role of booster doses of the vaccine needs to be highlighted. Methods Using a retrospective cohort study design emulating a target trial, we determined the relative effectiveness of a homologous booster dose...

Objectives This study evaluated messages and communication approaches for maternal immunization uptake in Kenya. We identified persuasive communication aspects that would inform maternal immunization attitudes, intent, and vaccine uptake. Methods We conducted a two-phased mixed methods study with pregnant women and their male partners in three reg...

Background The relationship between the use of nonpharmaceutical interventions and COVID-19 vaccination among U.S. child care providers remains unknown. If unvaccinated child care providers are also less likely to employ nonpharmaceutical interventions, then a vaccine mandate across child care programs may have larger health and safety benefits. M...

Parental hesitancy poses a serious threat to the success of the COVID-19 childhood vaccination campaign. We investigate whether adults' opinions on childhood vaccination can be influenced via two survey experiments in Italy (n=3,524 participants) and the UK (n=3,066 participants). Respondents were randomly assigned to: a “risk treatment” that highl...

SARS-CoV-2 Variants of Concern (VOCs) continue to reshape the trajectory of the COVID-19 pandemic. However, why some VOCs, like Omicron, become globally dominant while the spread of others is limited is not fully understood. To address this question, we investigated the VOC Mu, which was first identified in Colombia in late 2020. Our study demonstr...

What types of public health messages are effective at changing people’s beliefs and intentions to practice social distancing to slow the spread of COVID-19? We conducted two randomized experiments in summer 2020 that assigned respondents to read a public health message and then measured their beliefs and behavioral intentions across a wide variety...

Background Open online forums like Reddit provide an opportunity to quantitatively examine COVID-19 vaccine perceptions early in the vaccine timeline. We examine COVID-19 misinformation on Reddit following vaccine scientific announcements, in the initial phases of the vaccine timeline. Methods We collected all posts on Reddit (reddit.com) from Jan...

Background: Knowledge of the vaccine effectiveness (VE) of a third or booster vaccine dose in preventing SARS-CoV-2 infection or its consequences is critical in developing recommendations for their use. We determined the relative VE of a three vs. two doses of an mRNA vaccine in preventing symptomatic SARS-CoV-2 infection, hospitalization, and sev...

Background Recent global outbreaks of vaccine-preventable diseases, both before and since the coronavirus disease 2019 pandemic, have led to the introduction or strengthening of vaccine mandate policies to target vaccine refusal. Globally, there is wide variation in how governments and jurisdictions implement and enforce mandatory vaccination as we...

Importance There is no published national research reporting child care professionals’ physical health, depression, or stress during the COVID-19 pandemic. Given their central role in supporting children’s development, child care professionals’ overall physical and mental health is important. Objectives To evaluate the prevalence of chronic diseas...

The recent emergence of the SARS-CoV-2 Omicron variant is raising concerns because of its increased transmissibility and by its numerous spike mutations with potential to evade neutralizing antibodies elicited by COVID-19 vaccines. Here, we evaluated the effects of a heterologous BNT162b2 mRNA vaccine booster on the humoral immunity of participants...

Significance Chilblain diagnoses have increased during the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic and have been attributed to viral infection and a subsequent robust antiviral immune response. As a result, providers have managed these cases differently than idiopathic chilblains, which are associated with cold exposur...

This case series examines the differences in COVID-19 vaccine mandates for schoolteachers vs childcare professionals from US states that have implemented them.

Background: The 2014-2016 Ebola epidemic disrupted childhood immunization in Sierra Leone, Liberia, and Guinea. After the epidemic, the Government of Sierra Leone prioritized community engagement to increase vaccination confidence and uptake. To support these efforts, we examined potential drivers of vaccination confidence and uptake in Sierra Leo...

Background Persons on chronic hemodialysis have a significantly diminished humoral immune response to SARS-CoV-2 vaccines. Whether this translates to reduced vaccine effectiveness (VE) is unknown. Methods We used the US Department of Veterans Affairs COVID-19 Shared Data Resource to identify all Veterans who were tested for SARS-CoV-2 between Janu...