Clinical and economic outcomes associated with respiratory syncytial virus vaccination in older adults in the United States

Cost-effectiveness of Prefusion F Protein-based Vaccines Against Respiratory Syncytial Virus Disease for Older Adults in the United States

BACKGROUND

Two prefusion F protein-based vaccines, Arexvy and Abrysvo, have been authorized by the US Food and Drug Administration for protecting older adults against respiratory syncytial virus (RSV)-associated lower respiratory tract illness. We evaluated the health benefits and cost-effectiveness of these vaccines.

METHODS

We developed a discrete-event simulation model, parameterized with the burden of RSV disease including outpatient care, hospitalization, and death for adults aged 60 years or older in the United States. Taking into account the costs associated with these RSV-related outcomes, we calculated the net monetary benefit using quality-adjusted life-year (QALY) gained as a measure of effectiveness and determined the range of price-per-dose (PPD) for Arexvy and Abrysvo vaccination programs to be cost-effective from a societal perspective.

RESULTS

Using a willingness-to-pay of $95 000 per QALY gained, we found that vaccination programs could be cost-effective for a PPD up to $127 with Arexvy and $118 with Abrysvo over the first RSV season. Achieving an influenza-like vaccination coverage of 66% for the population of older adults in the United States, the budget impact of these programs at the maximum PPD ranged from $6.48 to $6.78 billion. If the benefits of vaccination extend to a second RSV season as reported in clinical trials, we estimated a maximum PPD of $235 for Arexvy and $245 for Abrysvo, with 2-year budget impacts of $11.78 and $12.25 billion, respectively.

CONCLUSIONS

Vaccination of older adults would provide substantial direct health benefits by reducing outcomes associated with RSV-related illness in this population.

Public Health Impact of the Adjuvanted RSVPreF3 Vaccine for Respiratory Syncytial Virus Prevention Among Older Adults in the United States

INTRODUCTION

Respiratory syncytial virus (RSV) is an important cause of lower respiratory tract disease in older adults, resulting in substantial morbidity and mortality.

METHODS

This study estimates the public health impact of vaccination with the adjuvanted RSVPreF3 vaccine among adults aged ≥ 60 years in the United States (US). A static, multi-cohort Markov model was used to estimate RSV-related outcomes over a 3-year time horizon for scenarios with and without one-time RSV vaccination. The base-case analysis assumed the same vaccination coverage as for influenza vaccines, with key epidemiology and vaccine inputs obtained from the published literature and phase 3 clinical trial results for the adjuvanted RSVPreF3 vaccine. Model outcomes included the clinical burden of RSV (symptomatic RSV acute respiratory illness [RSV-ARI] cases [classified as upper or lower respiratory tract disease], pneumonia complications, and mortality) and RSV-related healthcare resource use (hospitalizations, emergency department visits, outpatient visits, and antibiotic prescriptions).

RESULTS

In the base-case analysis, approximately 56.7 million adults aged ≥ 60 years received the vaccine, resulting in 2,954,465 fewer symptomatic RSV-ARI cases over 3 years compared with no vaccination, including 321,019 fewer X-ray confirmed pneumonia cases and 16,660 fewer RSV-related deaths. Vaccination also prevented a substantial number of RSV-related hospitalizations (203,891), emergency department visits (164,060), outpatient visits (1,577,586), and antibiotic prescriptions (1,343,915) over the 3-year period. A considerable public health impact was observed across a range of sensitivity analyses.

CONCLUSIONS

These findings highlight the potential of the adjuvanted RSVPreF3 vaccine to substantially reduce RSV disease burden among US older adults aged ≥ 60 years.

Respiratory Syncytial Virus Vaccines: Analysis of Pre-Marketing Clinical Trials for Immunogenicity in the Population over 50 Years of Age

Immunosenescence refers to age-related alterations in immune system function affecting both the humoral and cellular arm of immunity. Understanding immunosenescence and its impact on the vaccination of older adults is essential since primary vaccine responses in older individuals can fail to generate complete protection, especially vaccines targeting infections with increased incidence among the elderly, such as the respiratory syncytial virus. Here, we review clinical trials of both candidate and approved vaccines against respiratory syncytial virus (RSV) that include adults aged ≥50 years, with an emphasis on the evaluation of immunogenicity parameters. Currently, there are 10 vaccine candidates and 2 vaccines approved for the prevention of RSV in the older adult population. The number of registered clinical trials for this age group amounts to 42. Our preliminary evaluation of published results and interim analyses of RSV vaccine clinical trials indicates efficacy in older adult participants, demonstrating immunity levels that closely resemble those of younger adult participants.

Impact and cost-effectiveness analyses of vaccination for prevention of respiratory syncytial virus disease among older adults in Ontario: A Canadian Immunization Research Network (CIRN) study

BACKGROUND

Two prefusion F protein-based vaccines, Arexvy and Abrysvo, have been approved by Health Canada for protecting older adults against respiratory syncytial virus (RSV)-associated lower respiratory tract disease. We estimated the health benefits and cost-effectiveness of these vaccines under a publicly funded single-dose vaccination program in Ontario that targets residents of long-term care homes (LTCHs). Additionally, we evaluated an extended program that broadens vaccination to include community-dwelling older adults.

METHODS

A discrete-event simulation model was parameterised with the burden of RSV disease including outpatient care, hospitalisation, and death among adults aged 60 years or older in Ontario, Canada. Accounting for direct and indirect costs (in 2023 Canadian dollars) associated with RSV-related outcomes, we calculated the net monetary benefit using quality-adjusted life-year (QALY) gained, and determined the range of price-per-dose (PPD) for vaccination programs to be cost-effective from both healthcare and societal perspectives over two RSV seasons. The incremental cost-effectiveness ratio (ICER) was calculated to estimate the additional costs required to gain one QALY.

RESULTS

Using a willingness-to-pay of $50,000 per QALY gained, we found that vaccinating 90% of residents in LTCHs with Arexvy would be cost-effective from a societal perspective for a PPD up to $163, producing a mean ICER value of $49,984 (95% CI: $47,539 to $52,704) per QALY gained with a two-year budget impact of $463,468 per 100,000 older adults. The reduction of hospitalizations was estimated at 7.0% compared to the no-vaccination scenario. Extending the program to include community-dwelling older adults with a 74% coverage akin to influenza vaccination, Arexvy remains cost-effective for a PPD up to $139, with a mean ICER value of $49,698 (95% CI: 48,022 to 51,388) per QALY gained and a two-year budget impact of $8.63 million. Compared to the no-vaccination scenario, the extended program resulted in a 57.3% reduction in RSV-related hospitalisations.

CONCLUSIONS

Vaccinating residents of LTCHs against RSV disease would be cost-effective depending on PPD; extending the program to community-dwelling older adults would provide substantial health benefits, averting significant direct healthcare costs and productivity losses.

The relationship between autophagy and respiratory viruses

Respiratory viruses have caused severe global health problems and posed essential challenges to the medical community. In recent years, the role of autophagy as a critical process in cells in viral respiratory diseases has been noticed. One of the vital catabolic biological processes in the body is autophagy. Autophagy contributes to energy recovery by targeting and selectively directing foreign microorganisms, organelles, and senescent intracellular proteins to the lysosome for degradation and phagocytosis. Activation or suppression of autophagy is often initiated when foreign pathogenic organisms such as viruses infect cells. Because of its antiviral properties, several viruses may escape or resist this process by encoding viral proteins. Viruses can also use autophagy to enhance their replication or prolong the persistence of latent infections. Here, we provide an overview of autophagy and respiratory viruses such as coronavirus, rhinovirus, parainfluenza, influenza, adenovirus, and respiratory syncytial virus, and examine the interactions between them and the role of autophagy in the virus-host interaction process and the resulting virus replication strategy.

Efficacy and Safety of an mRNA-Based RSV PreF Vaccine in Older Adults

BACKGROUND

Respiratory syncytial virus (RSV) can cause substantial morbidity and mortality among older adults. An mRNA-based RSV vaccine, mRNA-1345, encoding the stabilized RSV prefusion F glycoprotein, is under clinical investigation.

METHODS

In this ongoing, randomized, double-blind, placebo-controlled, phase 2-3 trial, we randomly assigned, in a 1:1 ratio, adults 60 years of age or older to receive one dose of mRNA-1345 (50 μg) or placebo. The two primary efficacy end points were the prevention of RSV-associated lower respiratory tract disease with at least two signs or symptoms and with at least three signs or symptoms. A key secondary efficacy end point was the prevention of RSV-associated acute respiratory disease. Safety was also assessed.

RESULTS

Overall, 35,541 participants were assigned to receive the mRNA-1345 vaccine (17,793 participants) or placebo (17,748). The median follow-up was 112 days (range, 1 to 379). The primary analyses were conducted when at least 50% of the anticipated cases of RSV-associated lower respiratory tract disease had occurred. Vaccine efficacy was 83.7% (95.88% confidence interval [CI], 66.0 to 92.2) against RSV-associated lower respiratory tract disease with at least two signs or symptoms and 82.4% (96.36% CI, 34.8 to 95.3) against the disease with at least three signs or symptoms. Vaccine efficacy was 68.4% (95% CI, 50.9 to 79.7) against RSV-associated acute respiratory disease. Protection was observed against both RSV subtypes (A and B) and was generally consistent across subgroups defined according to age and coexisting conditions. Participants in the mRNA-1345 group had a higher incidence than those in the placebo group of solicited local adverse reactions (58.7% vs. 16.2%) and of systemic adverse reactions (47.7% vs. 32.9%); most reactions were mild to moderate in severity and were transient. Serious adverse events occurred in 2.8% of the participants in each trial group.

CONCLUSIONS

A single dose of the mRNA-1345 vaccine resulted in no evident safety concerns and led to a lower incidence of RSV-associated lower respiratory tract disease and of RSV-associated acute respiratory disease than placebo among adults 60 years of age or older. (Funded by Moderna; ConquerRSV ClinicalTrials.gov number, NCT05127434.).

Vaccination for Respiratory Syncytial Virus: A Narrative Review and Primer for Clinicians

Respiratory syncytial virus (RSV) poses a significant burden on public health, causing lower respiratory tract infections in infants, young children, older adults, and immunocompromised individuals. Recent development and licensure of effective RSV vaccines provide a promising approach to lessening the associated morbidity and mortality of severe infections. This narrative review aims to empower clinicians with the necessary knowledge to make informed decisions regarding RSV vaccination, focusing on the prevention and control of RSV infections, especially among vulnerable populations. The paper explores the available RSV vaccines and existing evidence regarding their efficacy and safety in diverse populations. Synthesizing this information for clinicians can help the latter understand the benefits and considerations associated with RSV vaccination, contributing to improved patient care and public health outcomes.

Respiratory Syncytial Virus Vaccines: A Review of the Candidates and the Approved Vaccines

Respiratory syncytial virus (RSV) is responsible for a significant proportion of global morbidity and mortality affecting young children and older adults. In the aftermath of formalin-inactivated RSV vaccine development, the effort to develop an immunizing agent was carefully guided by epidemiologic and pathophysiological evidence of the virus, including various vaccine technologies. The pipeline of RSV vaccine development includes messenger ribonucleic acid (mRNA), live-attenuated (LAV), subunit, and recombinant vector-based vaccine candidates targeting different virus proteins. The availability of vaccine candidates of various technologies enables adjustment to the individualized needs of each vulnerable age group. Arexvy® (GSK), followed by Abrysvo® (Pfizer), is the first vaccine available for market use as an immunizing agent to prevent lower respiratory tract disease in older adults. Abrysvo is additionally indicated for the passive immunization of infants by maternal administration during pregnancy. This review presents the RSV vaccine pipeline, analyzing the results of clinical trials. The key features of each vaccine technology are also mentioned. Currently, 24 vaccines are in the clinical stage of development, including the 2 licensed vaccines. Research in the field of RSV vaccination, including the pharmacovigilance methods of already approved vaccines, promotes the achievement of successful prevention.

Comparative Cost-Effectiveness Analysis of Respiratory Syncytial Virus Vaccines for Older Adults in Hong Kong

Two respiratory syncytial virus (RSV) vaccines (AREXVY® and ABRYSVO®) were recently approved for older adults in the US. This study aimed to evaluate the cost-effectiveness of AREXVY® and ABRYSVO® from the Hong Kong public healthcare provider's perspective. A two-year decision-analytical model was developed to examine the outcomes of a single RSV vaccination (AREXVY® or ABRYSVO®) compared to no vaccination. Primary outcomes included RSV-related health outcomes, direct medical costs, quality-adjusted life-year (QALY) loss, and incremental cost per QALY (ICER). RSV vaccines are not yet marketed in Hong Kong, base-case analysis, therefore, benchmarked US RSV vaccine prices at 4 levels (25%, 50%, 75%, 100%). AREXVY® and ABRYSVO® (versus no vaccination) gained 0.000568 QALY and 0.000647 QALY, respectively. ICERs of ABRYSVO® (26,209 USD/QALY) and AREXVY® (47,485 USD/QALY) were lower than the willingness-to-pay threshold (49,594 USD/QALY) at 25% US vaccine price. The RSV attack rate was a common influential factor at all vaccine price levels. The probabilities of AREXVY® and ABRYSVO® to be most cost-effective were 0.10% and 97.68%, respectively, at 25% US vaccine price. Single vaccination of ABRYSVO® or AREXVY® for older adults appears to gain QALYs over 2 years in Hong Kong. The cost-effectiveness of AREXVY® and ABRYSVO® is subject to vaccine price and RSV attack rate.

Cost-Effectiveness of Prefusion F Protein-Based Vaccines Against Respiratory Syncytial Virus Disease for Older Adults in the United States

Background

Two prefusion F protein-based vaccines, Arexvy and Abrysvo, have been authorized by the US Food and Drug Administration for protecting older adults against Respiratory Syncytial Virus (RSV)-associated lower respiratory tract illness. We evaluated the health benefits and cost-effectiveness of these vaccines.

Methods

We developed a discrete-event simulation model, parameterized with the burden of RSV disease including outpatient care, hospitalization, and death for adults aged 60 years or older in the US. Taking into account the costs associated with these RSV-related outcomes, we calculated the net monetary benefit using quality-adjusted life-years (QALY) gained as a measure of effectiveness, and determined the range of price-per-dose (PPD) for Arexvy and Abrysvo vaccination programs to be cost-effective from a societal perspective.

Results

Using a willingness-to-pay of $95,000 per QALY gained, we found that vaccination programs could be cost-effective for a PPD under $120 with Arexvy and $111 with Abrysvo over the first RSV season. Achieving an influenza-like vaccination coverage of 66% for the population of older adults in the US, the budget impact of these programs at the maximum PPD ranged from $5.74 to $6.10 billion. If the benefits of vaccination extend to a second RSV season as reported in clinical trials, we estimated a maximum PPD of $250 for Arexvy and $233 for Abrysvo, with two-year budget impacts of $11.59 and $10.89 billion, respectively.

Conclusions

Vaccination of older adults would provide substantial direct health benefits by reducing outcomes associated with RSV-related illness in this population.

Modeling Respiratory Syncytial Virus Adult Vaccination in the United States With a Dynamic Transmission Model

BACKGROUND

Respiratory syncytial virus (RSV) is shown to cause substantial morbidity, hospitalization, and mortality in infants and older adults. Population-level modeling of RSV allows to estimate the full burden of disease and the potential epidemiological impact of novel prophylactics.

METHODS

We modeled the RSV epidemiology in the United States across all ages using a deterministic compartmental transmission model. Population-level symptomatic RSV acute respiratory tract infection (ARI) cases were projected across different natural history scenarios with and without vaccination of adults aged ≥60 years. The impact of vaccine efficacy against ARIs, infectiousness and vaccine coverage on ARI incidence were assessed. The impact on medical attendance, hospitalization, complications, death, and other outcomes was also derived.

RESULTS

Without a vaccine, we project 17.5-22.6 million symptomatic RSV ARI cases annually in adults aged ≥18 years in the US, with 3.6-4.8 million/year occurring in adults aged ≥60 years. Modeling indicates that up to 2.0 million symptomatic RSV-ARI cases could be prevented annually in ≥60-year-olds with a hypothetical vaccine (70% vaccine efficacy against symptomatic ARI and 60% vaccine coverage) and that up to 0.69 million/year could be prevented in the nonvaccinated population, assuming 50% vaccine impact on infectiousness.

CONCLUSIONS

The model provides estimated burden of RSV in the US across all age groups, with substantial burden projected specifically in older adults. Vaccination of adults aged ≥60 years could significantly reduce the burden of disease in this population, with additional indirect effect in adults aged <60 years due to reduced transmissibility.

Predicted Public Health and Economic Impact of Respiratory Syncytial Virus Vaccination with Variable Duration of Protection for Adults ≥60 Years in Belgium

Respiratory syncytial virus (RSV) is a leading cause of acute respiratory infection (ARI) in older adults. This study used a static, cohort-based decision-tree model to estimate the public health and economic impact of vaccination against RSV in Belgians aged ≥60 years compared with no vaccination for different vaccine duration of protection profiles from a healthcare payer perspective. Three vaccine protection durations were compared (1, 3, and 5 years), and several sensitivity and scenario analyses were performed. Results showed that an RSV vaccine with a 3-year duration of protection would prevent 154,728 symptomatic RSV-ARI cases, 3688 hospitalizations, and 502 deaths over three years compared to no vaccination in older adults and would save EUR 35,982,857 in direct medical costs in Belgium. The number needed to vaccinate to prevent one RSV-ARI case was 11 for the 3-year duration profile, while it was 28 and 8 for the 1- and 5-year vaccine duration profiles, respectively. The model was generally robust in sensitivity analyses varying key input values. This study suggested that vaccination could substantially decrease the public health and economic burden of RSV in adults ≥60 years in Belgium, with benefits increasing with a longer duration of vaccine protection.

Monoclonal antibodies for prophylaxis and therapy of respiratory syncytial virus, SARS-CoV-2, human immunodeficiency virus, rabies and bacterial infections: an update from the World Association of Infectious Diseases and Immunological Disorders and the Italian Society of Antinfective Therapy

Monoclonal antibodies (mABs) are safe and effective proteins produced in laboratory that may be used to target a single epitope of a highly conserved protein of a virus or a bacterial pathogen. For this purpose, the epitope is selected among those that play the major role as targets for prevention of infection or tissue damage. In this paper, characteristics of the most important mABs that have been licensed and used or are in advanced stages of development for use in prophylaxis and therapy of infectious diseases are discussed. We showed that a great number of mABs effective against virus or bacterial infections have been developed, although only in a small number of cases these are licensed for use in clinical practice and have reached the market. Although some examples of therapeutic efficacy have been shown, not unlike more traditional antiviral or antibacterial treatments, their efficacy is significantly greater in prophylaxis or early post-exposure treatment. Although in many cases the use of vaccines is more effective and cost-effective than that of mABs, for many infectious diseases no vaccines have yet been developed and licensed. Furthermore, in emergency situations, like in epidemics or pandemics, the availability of mABs can be an attractive adjunct to our armament to reduce the impact. Finally, the availability of mABs against bacteria can be an important alternative, when multidrug-resistant strains are involved.

Economic burden of respiratory syncytial virus infection in adults: a systematic literature review

AIMS

Capture the economic and healthcare resource utilization (HCRU) burden in older adults due to respiratory syncytial virus (RSV) infection.

METHODS

An electronic literature search of PubMed, Embase, the Cochrane Library, PsycINFO, and EconLit was conducted for studies of the cost and HCRU outcomes of RSV infection in adult patients, with no language or country restrictions. Search dates for primary studies were January 1, 2002-May 18, 2022. The methodological quality of included studies was assessed using a modification of the Critical Appraisal Skills Programme (CASP) checklist for economic studies and the Drummond checklist.

RESULTS

42 studies were identified that reported cost or HCRU data associated with RSV infections, with geographic locations across North America, South America, Europe, Asia, and Oceania. Generally, hospitalization costs were highest in the United States (US). Driving factors of increased cost included older age, comorbidities, and length of stay. US studies found that the national direct cost burden of RSV hospitalizations was $1.3 billion for all adults and $1.5-$4.0 billion for adults aged ≥60 years (estimates for other countries were not identified). Studies estimating incremental costs for RSV cases versus controls and costs pre- and post-RSV infection demonstrated higher costs for RSV cases. Hospitalizations accounted for the majority of total costs.

Incidence of Respiratory Syncytial Virus Infection in Older Adults Before and During the COVID-19 Pandemic

Importance

Little is known about the burden and outcomes of respiratory syncytial virus (RSV)-positive acute respiratory infection (ARI) in community-dwelling older adults.

Objective

To assess the incidence of RSV-positive ARI before and during the COVID-19 pandemic, and to assess outcomes for RSV-positive ARI in older adults.

Design, Setting, and Participants

This was a community-based cohort study of adults residing in southeast Minnesota that followed up with 2325 adults aged 50 years or older for 2 RSV seasons (2019-2021) to assess the incidence of RSV-positive ARI. The study assessed outcomes at 2 to 4 weeks, 6 to 7 months, and 12 to 13 months after RSV-positive ARI.

Exposure

RSV-positive and -negative ARI.

Main Outcomes and Measures

RSV status was the main study outcome. Incidence and attack rates of RSV-positive ARI were calculated during each RSV season, including before (October 2019 to April 2020) and during (October 2020 to April 2021) COVID-19 pandemic, and further calculated during non-RSV season (May to September 2021) for assessing impact of COVID-19. The self-reported quality of life (QOL) by Short-Form Health Survey-36 (SF-36) and physical functional measures (eg, 6-minute walk and spirometry) at each time point was assessed.

Results

In this study of 2325 participants, the median (range) age of study participants was 67 (50-98) years, 1380 (59%) were female, and 2240 (96%) were non-Hispanic White individuals. The prepandemic incidence rate of RSV-positive ARI was 48.6 (95% CI, 36.9-62.9) per 1000 person-years with a 2.50% (95% CI, 1.90%-3.21%) attack rate. No RSV-positive ARI case was identified during the COVID-19 pandemic RSV season. Incidence of 10.2 (95% CI, 4.1-21.1) per 1000 person-years and attack rate of 0.42%; (95% CI, 0.17%-0.86%) were observed during the summer of 2021. Based on prepandemic RSV season results, participants with RSV-positive ARI (vs matched RSV-negative ARI) reported significantly lower QOL adjusted mean difference (limitations due to physical health, -16.7 [95% CI, -31.8 to -1.8]; fatigue, -8.4 [95% CI, -14.3 to -2.4]; and difficulty in social functioning, -11.9 [95% CI, -19.8 to -4.0] within 2 to 4 weeks after RSV-positive ARI [ie, short-term outcome]). Compared with participants with RSV-negative ARI, those with RSV-positive ARI also had lower QOL (fatigue: -4.0 [95% CI, -8.5 to -1.3]; difficulty in social functioning, -5.8 [95% CI, -10.3 to -1.3]; and limitation due to emotional problem, -7.0 [95% CI, -12.7 to -1.3] at 6 to 7 months after RSV-positive ARI [intermediate-term outcome]; fatigue, -4.4 [95% CI, -7.3 to -1.5]; difficulty in social functioning, -5.2 [95% CI, -8.7 to -1.7] and limitation due to emotional problem, -5.7 [95% CI, -10.7 to -0.6] at 12-13 months after RSV-positive ARI [ie, long-term outcomes]) independent of age, sex, race and/or ethnicity, socioeconomic status, and high-risk comorbidities.

Conclusions and Relevance

In this cohort study, the burden of RSV-positive ARI in older adults during the pre-COVID-19 period was substantial. After a reduction of RSV-positive ARI incidence from October 2020 to April 2021, RSV-positive ARI re-emerged during the summer of 2021. RSV-positive ARI was associated with significant long-term lower QOL beyond the short-term lower QOL in older adults.

Respiratory syncytial virus prevention within reach: the vaccine and monoclonal antibody landscape

Respiratory syncytial virus is the second most common cause of infant mortality and a major cause of morbidity and mortality in older adults (aged >60 years). Efforts to develop a respiratory syncytial virus vaccine or immunoprophylaxis remain highly active. 33 respiratory syncytial virus prevention candidates are in clinical development using six different approaches: recombinant vector, subunit, particle-based, live attenuated, chimeric, and nucleic acid vaccines; and monoclonal antibodies. Nine candidates are in phase 3 clinical trials. Understanding the epitopes targeted by highly neutralising antibodies has resulted in a shift from empirical to rational and structure-based vaccine and monoclonal antibody design. An extended half-life monoclonal antibody for all infants is likely to be within 1 year of regulatory approval (from August, 2022) for high-income countries. Live-attenuated vaccines are in development for older infants (aged >6 months). Subunit vaccines are in late-stage trials for pregnant women to protect infants, whereas vector, subunit, and nucleic acid approaches are being developed for older adults. Urgent next steps include ensuring access and affordability of a respiratory syncytial virus vaccine globally. This review gives an overview of respiratory syncytial virus vaccines and monoclonal antibodies in clinical development highlighting different target populations, antigens, and trial results.