Why and How Vaccines Work.

Vaccines save millions of lives from infectious diseases caused by viruses and bacteria. As the world awaits safe and effective COVID-19 vaccines, we celebrate the progresses made and highlight challenges ahead in vaccines and the science behind them.

Coast-to-Coast Spread of SARS-CoV-2 during the Early Epidemic in the United States.

The novel coronavirus SARS-CoV-2 was first detected in the Pacific Northwest region of the United States in January 2020, with subsequent COVID-19 outbreaks detected in all 50 states by early March. To uncover the sources of SARS-CoV-2 introductions and patterns of spread within the United States, we sequenced nine viral genomes from early reported COVID-19 patients in Connecticut. Our phylogenetic analysis places the majority of these genomes with viruses sequenced from Washington state. By coupling our genomic data with domestic and international travel patterns, we show that early SARS-CoV-2 transmission in Connecticut was likely driven by domestic introductions. Moreover, the risk of domestic importation to Connecticut exceeded that of international importation by mid-March regardless of our estimated effects of federal travel restrictions. This study provides evidence of widespread sustained transmission of SARS-CoV-2 within the United States and highlights the critical need for local surveillance.

Distinguishing features of long COVID identified through immune profiling.

Post-acute infection syndromes may develop after acute viral disease1. 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 dysfunctions2-4. However, the biological processes that are associated with the development and persistence of these symptoms are unclear. Here 275 individuals with or without long COVID were enrolled in a cross-sectional study that included multidimensional immune phenotyping and unbiased machine learning methods to identify biological features associated with long COVID. Marked differences were noted in circulating myeloid and lymphocyte populations relative to the matched controls, as well as evidence of exaggerated humoral responses directed against SARS-CoV-2 among participants with long COVID. Furthermore, higher antibody responses directed against non-SARS-CoV-2 viral pathogens were observed among individuals with long COVID, particularly Epstein-Barr virus. Levels of soluble immune mediators and hormones varied among groups, with cortisol levels being lower among participants with long COVID. Integration of immune phenotyping data into unbiased machine learning models identified the key features that are most strongly associated with long COVID status. Collectively, these findings may help to guide future studies into the pathobiology of long COVID and help with developing relevant biomarkers.

Impact of circulating SARS-CoV-2 variants on mRNA vaccine-induced immunity.

The emergence of SARS-CoV-2 variants with mutations in major neutralizing antibody-binding sites can affect humoral immunity induced by infection or vaccination1-6. Here we analysed the development of anti-SARS-CoV-2 antibody and T cell responses in individuals who were previously infected (recovered) or uninfected (naive) and received mRNA vaccines to SARS-CoV-2. While individuals who were previously infected sustained higher antibody titres than individuals who were uninfected post-vaccination, the latter reached comparable levels of neutralization responses to the ancestral strain after the second vaccine dose. T cell activation markers measured upon spike or nucleocapsid peptide in vitro stimulation showed a progressive increase after vaccination. Comprehensive analysis of plasma neutralization using 16 authentic isolates of distinct locally circulating SARS-CoV-2 variants revealed a range of reduction in the neutralization capacity associated with specific mutations in the spike gene: lineages with E484K and N501Y/T (for example, B.1.351 and P.1) had the greatest reduction, followed by lineages with L452R (for example, B.1.617.2). While both groups retained neutralization capacity against all variants, plasma from individuals who were previously infected and vaccinated displayed overall better neutralization capacity than plasma from individuals who were uninfected and also received two vaccine doses, pointing to vaccine boosters as a relevant future strategy to alleviate the effect of emerging variants on antibody neutralizing activity.

Longitudinal analyses reveal immunological misfiring in severe COVID-19.

Recent studies have provided insights into the pathogenesis of coronavirus disease 2019 (COVID-19)1-4. However, the longitudinal immunological correlates of disease outcome remain unclear. Here we serially analysed immune responses in 113 patients with moderate or severe COVID-19. Immune profiling revealed an overall increase in innate cell lineages, with a concomitant reduction in T cell number. An early elevation in cytokine levels was associated with worse disease outcomes. Following an early increase in cytokines, patients with moderate COVID-19 displayed a progressive reduction in type 1 (antiviral) and type 3 (antifungal) responses. By contrast, patients with severe COVID-19 maintained these elevated responses throughout the course of the disease. Moreover, severe COVID-19 was accompanied by an increase in multiple type 2 (anti-helminths) effectors, including interleukin-5 (IL-5), IL-13, immunoglobulin E and eosinophils. Unsupervised clustering analysis identified four immune signatures, representing growth factors (A), type-2/3 cytokines (B), mixed type-1/2/3 cytokines (C), and chemokines (D) that correlated with three distinct disease trajectories. The immune profiles of patients who recovered from moderate COVID-19 were enriched in tissue reparative growth factor signature A, whereas the profiles of those with who developed severe disease had elevated levels of all four signatures. Thus, we have identified a maladapted immune response profile associated with severe COVID-19 and poor clinical outcome, as well as early immune signatures that correlate with divergent disease trajectories.

Sex differences in immune responses that underlie COVID-19 disease outcomes.

There is increasing evidence that coronavirus disease 2019 (COVID-19) produces more severe symptoms and higher mortality among men than among women1-5. However, whether immune responses against severe acute respiratory syndrome coronavirus (SARS-CoV-2) differ between sexes, and whether such differences correlate with the sex difference in the disease course of COVID-19, is currently unknown. Here we examined sex differences in viral loads, SARS-CoV-2-specific antibody titres, plasma cytokines and blood-cell phenotyping in patients with moderate COVID-19 who had not received immunomodulatory medications. Male patients had higher plasma levels of innate immune cytokines such as IL-8 and IL-18 along with more robust induction of non-classical monocytes. By contrast, female patients had more robust T cell activation than male patients during SARS-CoV-2 infection. Notably, we found that a poor T cell response negatively correlated with patients' age and was associated with worse disease outcome in male patients, but not in female patients. By contrast, higher levels of innate immune cytokines were associated with worse disease progression in female patients, but not in male patients. These findings provide a possible explanation for the observed sex biases in COVID-19, and provide an important basis for the development of a sex-based approach to the treatment and care of male and female patients with COVID-19.

No evidence of fetal defects or anti-syncytin-1 antibody induction following COVID-19 mRNA vaccination.

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 abnormalities; and (2) whether COVID-19 mRNA-vaccinated human volunteers exhibit elevated levels of antibodies to the human placental protein syncytin-1. Using a mouse model, we found that intramuscular COVID-19 mRNA vaccination during early pregnancy at gestational age E7.5 did not lead to differences in fetal size by crown-rump length or weight at term, nor did we observe any gross birth defects. In contrast, injection of the TLR3 agonist and double-stranded RNA mimic polyinosinic-polycytidylic acid, or poly(I:C), impacted growth in utero leading to reduced fetal size. No overt maternal illness following either vaccination or poly(I:C) exposure was observed. We also found that term fetuses from these murine pregnancies vaccinated prior to the formation of the definitive placenta exhibit high circulating levels of anti-spike and anti-receptor-binding domain (anti-RBD) antibodies to Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) consistent with maternal antibody status, indicating transplacental transfer in the later stages of pregnancy after early immunization. Finally, we did not detect increased levels of circulating anti-syncytin-1 antibodies in a cohort of COVID-19 vaccinated adults compared to unvaccinated adults by ELISA. Our findings contradict popular claims associating COVID-19 mRNA vaccination with infertility and adverse neonatal outcomes.

Nirmatrelvir/Ritonavir Use and Hospitalizations or Death in a Previously Uninfected Nonhospitalized High-Risk Population With COVID-19: A Matched Cohort Study.

OBJECTIVE: To determine the association of nirmatrelvir/ritonavir (NMV/r) with hospitalization or death within 30 days as compared with untreated controls previously uninfected and nonhospitalized. METHODS: We used a matched cohort design using inverse probability of treatment weight (IPTW). Individuals prescribed NMV/r within 3 days of COVID-19 diagnosis were compared with IPTW-based untreated controls. Variables for IPTW included age, race, sex, body mass index, geographic location, vaccination status, and multiple comorbidities. Additional analyses were conducted on NMV/r-treated and propensity score-matched untreated controls. RESULTS: Among 7615 individuals prescribed NMV/r and 62 077 controls identified between 1 January 2022 and 25 February 2023, the risk of hospitalization/death was lower among NMV/r-treated persons vs untreated controls (243 vs 3468 events; absolute risk difference [ARD], -2.36 [95% CI, -2.57 to -2.14]). The difference was significant for those >60 and ≤60 years old (ARD, -3.86 [95% CI, -4.19 to -3.54] vs -0.27 [95% CI, -0.51 to -0.03]) and for persons asymptomatic and symptomatic (ARD, -7.09 [95% CI, -7.62 to -6.55] vs -1.46 [95% CI, -1.66 to -1.25]). Significant benefit was observed among individuals unvaccinated and vaccinated, with or without a booster dose. CONCLUSIONS: NMV/r is associated with a significant reduction in 30-day hospitalization or death among individuals previously uninfected and nonhospitalized.

Incorporating Efficacy Data from Initial Trials Into Subsequent Evaluations: Application to Vaccines Against Respiratory Syncytial Virus.

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 the availability of effective vaccines. METHODS: Based on the outcomes from a failed trial of a maternal vaccine against respiratory syncytial virus (RSV), we simulated data for a new Bayesian group-sequential trial. We analyzed the data either ignoring data from the previous trial (i.e., weakly informative prior distributions) or using prior distributions incorporating the historical data into the analysis. We evaluated scenarios where efficacy in the new trial was the same, greater than, or less than that in the original trial. For each scenario, we evaluated the statistical power and type I error rate for estimating the vaccine effect following interim analyses. RESULTS: When we used a stringent threshold to control the type I error rate, analyses incorporating historical data had a small advantage over trials that did not. If control of type I error is less important (e.g., in a postlicensure evaluation), the incorporation of historical data can provide a substantial boost in efficiency. CONCLUSIONS: Due to the need to control the type I error rate in trials used to license a vaccine, incorporating historical data provides little additional benefit in terms of stopping the trial early. However, these statistical approaches could be promising in evaluations that use real-world evidence following licensure.

The importance of immunization in cancer prevention, treatment, and survivorship.

Answer questions and earn CME/CNE A measles outbreak originating in California during 2014 and 2015 called attention to the potential for infectious disease outbreaks related to underimmunized populations in the United States and the potential risk to pediatric patients with cancer attending school when such outbreaks occur. Compliance with vaccine recommendations is important for the prevention of hepatitis B-related and human papillomavirus-related cancers and for protecting immunocompromised patients with cancer, and these points are often overlooked, resulting in the continued occurrence of vaccine-preventable neoplastic and infectious diseases and complications. This article provides an overview of the importance of vaccines in the context of cancer and encourages clinician, health system, and public policy efforts to promote adherence to immunization recommendations in the United States. CA Cancer J Clin 2017;67:398-410. © 2017 American Cancer Society.

Persuading US White evangelicals to vaccinate for COVID-19: Testing message effectiveness in fall 2020 and spring 2021.

The development of COVID-19 vaccines was an important breakthrough for ending the pandemic. However, people refusing to get vaccinated diminish the level of community protection afforded to others. In the United States, White evangelicals have proven to be a particularly difficult group to convince to get vaccinated. Here we investigate whether this group can be persuaded to get vaccinated. To do this, we leverage data from two survey experiments, one fielded prior to approval of COVID-19 vaccines (study 1) and one fielded after approval (study 2). In both experiments, respondents were randomly assigned to treatment messages to promote COVID-19 vaccination. In study 1, we find that a message that emphasizes community interest and reciprocity with an invocation of embarrassment for choosing not to vaccinate is the most effective at increasing uptake intentions, while values-consistent messaging appears to be ineffective. In contrast, in study 2 we observe that this message is no longer effective and that most messages produce little change in vaccine intent. This inconsistency may be explained by the characteristics of White evangelicals who remain unvaccinated vis à vis those who got vaccinated. These results demonstrate the importance of retesting messages over time, the apparent limitations of values-targeted messaging, and document the need to consider heterogeneity even within well-defined populations. This work also cautions against drawing broad conclusions from studies carried out at a single point in time during the COVID-19 pandemic.

Measuring voluntary and policy-induced social distancing behavior during the COVID-19 pandemic.

Staying home and avoiding unnecessary contact is an important part of the effort to contain COVID-19 and limit deaths. Every state in the United States enacted policies to encourage distancing and some mandated staying home. Understanding how these policies interact with individuals' voluntary responses to the COVID-19 epidemic is a critical initial step in understanding the role of these nonpharmaceutical interventions in transmission dynamics and assessing policy impacts. We use variation in policy responses along with smart device data that measures the amount of time Americans stayed home to disentangle the extent that observed shifts in staying home behavior are induced by policy. We find evidence that stay-at-home orders and voluntary response to locally reported COVID-19 cases and deaths led to behavioral change. For the median county, which implemented a stay-at-home order with about two cases, we find that the response to stay-at-home orders increased time at home as if the county had experienced 29 additional local cases. However, the relative effect of stay-at-home orders was much greater in select counties. On the one hand, the mandate can be viewed as displacing a voluntary response to this rise in cases. On the other hand, policy accelerated the response, which likely helped reduce spread in the early phase of the pandemic. It is important to be able to attribute the relative role of self-interested behavior or policy mandates to understand the limits and opportunities for relying on voluntary behavior as opposed to imposing stay-at-home orders.

"Vaccinating your child during an emergency is more important than ever": a randomised controlled trial on message framing among Ukrainian refugees in Poland, 2023.

BackgroundSince 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.AimWe investigate the determinants of vaccination intention in refugee mothers from Ukraine residing in Poland and test the effect of three message frames.MethodsParticipants were randomised into either a control group or one of three intervention groups encouraging vaccination using a specific frame: (i) trust in the Polish health system, (ii) ease of access to vaccination or (iii) risk aversion. Primary outcomes were intention to vaccinate a child in Poland and clicking on a vaccination scheduling link.ResultsThe study was completed by 1,910 Ukrainian refugee mothers. Compared with the control group, the risk aversion message significantly increased vaccination intention (adjusted odds ratio (AOR): 2.35, 95% confidence interval (CI): 1.25-4.42) and clicking on the vaccine scheduling link (AOR: 1.53, 95% CI: 1.12-2.09). Messages around trust and ease of access did not have an effect. Important determinants of vaccination intention were perceived importance of vaccination (AOR: 1.12 95% CI: 1.01-1.25) and trusting vaccination information official health institutes (AOR: 1.40 95% CI: 1.06-1.83) and social media (AOR: 2.09 95% CI: 1.33-3.27).DiscussionUsing a risk aversion frame highlighting the vulnerability to infection that refugees face resulted in increased vaccination intention and clicks on a vaccination scheduler. Health workers who interact with Ukrainian refugees could use this frame in their vaccination communication.

Molnupiravir Use and 30-Day Hospitalizations or Death in a Previously Uninfected Nonhospitalized High-risk Population With COVID-19.

BACKGROUND: Clinical benefit of molnupiravir (MPV) in coronavirus disease 2019 (COVID-19)-infected subpopulations 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 nonhospitalized, previously uninfected Veterans with a first confirmed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection between 1 January and 31 August 2022, who were prescribed MPV within 3 days of COVID-19 diagnosis, and matched individuals who were not prescribed MPV. RESULTS: Among 1459 matched pairs, the incidence of hospitalization/death was not different among MPV treated versus untreated controls (48 vs 44 cases; absolute risk difference [ARD], 0.27; 95% confidence interval [CI], -.94 to 1.49). No benefit was observed among those >60 or ≤60 years old (ARD, 0.27; 95% CI, -1.25 to 1.79 vs ARD, -0.29; 95% CI, -1.22 to 1.80), those with specific comorbidities, or by vaccination status. A significant benefit was observed in asymptomatic but not in symptomatic persons (ARD, -2.80; 95% CI, -4.74 to -.87 vs ARD, 1.12; 95% CI -.31 to 2.55). Kaplan-Meier curves did not show a difference in proportion of persons who were hospitalized or died among MPV treated compared with untreated controls (logrank P = .7). CONCLUSIONS: MPV was not associated with a reduction in hospitalization or death within 30 days of COVID-19 diagnosis. A subgroup of patients presenting without symptoms experienced a benefit.

Global, regional, and national disease burden estimates of acute lower respiratory infections due to respiratory syncytial virus in children younger than 5 years in 2019: a systematic analysis.

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 community surveillance studies have been done to obtain a more precise estimation of RSV associated community deaths. We aimed to update RSV-associated acute lower respiratory infection morbidity and mortality at global, regional, and national levels in children aged 0-60 months for 2019, with focus on overall mortality and narrower infant age groups that are targeted by RSV prophylactics in development. METHODS: In this systematic analysis, we expanded our global RSV disease burden dataset by obtaining new data from an updated search for papers published between Jan 1, 2017, and Dec 31, 2020, from MEDLINE, Embase, Global Health, CINAHL, Web of Science, LILACS, OpenGrey, CNKI, Wanfang, and ChongqingVIP. We also included unpublished data from RSV GEN collaborators. Eligible studies reported data for children aged 0-60 months with RSV as primary infection with acute lower respiratory infection in community settings, or acute lower respiratory infection necessitating hospital admission; reported data for at least 12 consecutive months, except for in-hospital case fatality ratio (CFR) or for where RSV seasonality is well-defined; and reported incidence rate, hospital admission rate, RSV positive proportion in acute lower respiratory infection hospital admission, or in-hospital CFR. Studies were excluded if case definition was not clearly defined or not consistently applied, RSV infection was not laboratory confirmed or based on serology alone, or if the report included fewer than 50 cases of acute lower respiratory infection. We applied a generalised linear mixed-effects model (GLMM) to estimate RSV-associated acute lower respiratory infection incidence, hospital admission, and in-hospital mortality both globally and regionally (by country development status and by World Bank Income Classification) in 2019. We estimated country-level RSV-associated acute lower respiratory infection incidence through a risk-factor based model. We developed new models (through GLMM) that incorporated the latest RSV community mortality data for estimating overall RSV mortality. This review was registered in PROSPERO (CRD42021252400). FINDINGS: In addition to 317 studies included in our previous review, we identified and included 113 new eligible studies and unpublished data from 51 studies, for a total of 481 studies. We estimated that globally in 2019, there were 33·0 million RSV-associated acute lower respiratory infection episodes (uncertainty range [UR] 25·4-44·6 million), 3·6 million RSV-associated acute lower respiratory infection hospital admissions (2·9-4·6 million), 26 300 RSV-associated acute lower respiratory infection in-hospital deaths (15 100-49 100), and 101 400 RSV-attributable overall deaths (84 500-125 200) in children aged 0-60 months. In infants aged 0-6 months, we estimated that there were 6·6 million RSV-associated acute lower respiratory infection episodes (4·6-9·7 million), 1·4 million RSV-associated acute lower respiratory infection hospital admissions (1·0-2·0 million), 13 300 RSV-associated acute lower respiratory infection in-hospital deaths (6800-28 100), and 45 700 RSV-attributable overall deaths (38 400-55 900). 2·0% of deaths in children aged 0-60 months (UR 1·6-2·4) and 3·6% of deaths in children aged 28 days to 6 months (3·0-4·4) were attributable to RSV. More than 95% of RSV-associated acute lower respiratory infection episodes and more than 97% of RSV-attributable deaths across all age bands were in low-income and middle-income countries (LMICs). INTERPRETATION: RSV contributes substantially to morbidity and mortality burden globally in children aged 0-60 months, especially during the first 6 months of life and in LMICs. We highlight the striking overall mortality burden of RSV disease worldwide, with one in every 50 deaths in children aged 0-60 months and one in every 28 deaths in children aged 28 days to 6 months attributable to RSV. For every RSV-associated acute lower respiratory infection in-hospital death, we estimate approximately three more deaths attributable to RSV in the community. RSV passive immunisation programmes targeting protection during the first 6 months of life could have a substantial effect on reducing RSV disease burden, although more data are needed to understand the implications of the potential age-shifts in peak RSV burden to older age when these are implemented. FUNDING: EU Innovative Medicines Initiative Respiratory Syncytial Virus Consortium in Europe (RESCEU).

Detection of SARS-CoV-2 RNA by multiplex RT-qPCR.

The current quantitative reverse transcription PCR (RT-qPCR) assay recommended for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) testing in the United States requires analysis of 3 genomic targets per sample: 2 viral and 1 host. To simplify testing and reduce the volume of required reagents, we devised a multiplex RT-qPCR assay to detect SARS-CoV-2 in a single reaction. We used existing N1, N2, and RP primer and probe sets by the Centers for Disease Control and Prevention, but substituted fluorophores to allow multiplexing of the assay. The cycle threshold (Ct) values of our multiplex RT-qPCR were comparable to those obtained by the single assay adapted for research purposes. Low copy numbers (≥500 copies/reaction) of SARS-CoV-2 RNA were consistently detected by the multiplex RT-qPCR. Our novel multiplex RT-qPCR improves upon current single diagnostics by saving reagents, costs, time, and labor.

Postmortem minimally invasive tissue sampling in communities: exploring perceptions of families, funeral workers, religious and community leaders and healthcare providers from Pakistan.

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 members and healthcare providers regarding the feasibility of implementing MITS in community settings. METHODS: A qualitative exploratory study was conducted. A total of twenty one in-depth interviews were conducted with deceased infants' parents, elders of the family, religious leaders, community leaders, and funeral workers. Focus group discussions were conducted with health care providers (n = 14) in two peri-urban slum areas of Karachi, Pakistan. The duration of this study was from August to October 2020. Data was analyzed using thematic analysis and was coded and merged into categories forming eight major themes. RESULTS: In general, participants viewed minimally invasive tissue sampling (MITS) as beneficial for improving child health, though some had concerns about disrespecting the deceased during sample collection. Misinformation, fear of needles, and medical procedures were major barriers to MITS implementation. To enhance acceptance, community and religious leaders suggested using religious rulings, obtaining parental consent, ensuring confidentiality, and increasing efforts of community engagement. Community healthcare providers, along with funeral workers, recommended providing community members with grief counseling to increase study participation. Besides concerns about sampling interfering with respect for the decease, community members also raised concerns about misinformation. Further, participants provided feedback on the design and appearance of the mobile van used to collect MITS samples from children under the age of five. CONCLUSION: This study is critical for understanding the challenges associated with implementation of community-based MITS sampling in Pakistan. Integrating the use of a mobile van for sample collection, grief counseling along with community engagement sessions and advocacy will help address community-based misinformation and develop community trust.

Mental Health Impact of COVID-19 among Children and College Students: A Systematic Review.

The COVID-19 pandemic led to a worldwide lockdown and school closures, which have placed a substantial mental health burden on children and college students. Through a systematic search of the literature on PubMed and Collabovid of studies published January 2020-July 2021, our findings of five studies on children and 16 studies on college students found that both groups reported feeling more anxious, depressed, fatigued, and distressed than prior to the pandemic. Several risk factors such as living in rural areas, low family socioeconomic status, and being a family member or friend to a healthcare worker were strongly associated with worse mental health outcomes. As schools and researchers discuss future strategies on how to combine on-site teaching with online courses, our results indicate the importance of considering social contacts in students' mental health to support students at higher risk of social isolation during the COVID-19 pandemic.

The Association of Coronavirus Disease 2019 Risk Perception, County Death Rates, and Voluntary Health Behaviors Among United States Adult Population.

BACKGROUND: The coronavirus disease 2019 (COVID-19) pandemic continues to adversely impact the United States socially, culturally, and economically. The purpose of this study was to understand the relationship between COVID-19 county death rates, risk perception, and US adults' voluntary behaviors-particularly physical distancing. METHODS: Data were collected from CloudResearch/Qualtrics, Johns Hopkins University, the American Community Survey, and SafeGraph. RESULTS: Our results indicated that higher COVID-19 county death rates were associated with higher risk perceptions, leading to greater time spent at home. CONCLUSIONS: These findings will help public health officials identify strategies that best encourage voluntary health behaviors to help curb the spread of COVID-19.