Respiratory syncytial virus vaccination strategies for older Canadian adults: a cost-utility analysis.

BACKGROUND: Respiratory syncytial virus (RSV) vaccines could reduce disease burden and costs in older Canadian adults, but vaccination program cost-effectiveness is unknown. We evaluated the cost-effectiveness of different age cut-offs for RSV adult vaccination programs, with or without a focus on people with higher disease risk due to chronic medical conditions. METHODS: We developed a static individual-based model of medically attended RSV disease to compare alternative age-, medical risk-, and age-plus medical risk-based vaccination policies. The model followed a multiage population of 100 000 people aged 50 years and older. Vaccine characteristics were based on RSV vaccines authorized in Canada as of May 2024, with vaccine protection assumed to last 2 years (or 3 years in scenario analyses). We calculated sequential incremental cost-effectiveness ratios in 2023 Canadian dollars per quality-adjusted life year (QALY) from the health-system and societal perspectives, discounted at 1.5%. RESULTS: Although all vaccination strategies averted medically attended RSV disease, universal age-based strategies were not an efficient use of resources compared with medical risk-based strategies. Vaccinating adults aged 70 years and older with 1 or more chronic medical condition was the optimal strategy for a cost-effectiveness threshold of $50 000 per QALY. Results were sensitive to assumptions about vaccine price, but medical risk-based approaches remained optimal compared with age-based strategies, even when vaccine prices were low. Findings were robust to a range of alternative assumptions. INTERPRETATION: Vaccination programs for RSV in some groups of older Canadians with underlying medical conditions are likely cost-effective. These findings can inform the design of vaccination programs.

Cost-effectiveness of RSVpreF vaccine and nirsevimab for the prevention of respiratory syncytial virus disease in Canadian infants.

BACKGROUND: Health Canada recently authorized the RSVpreF pregnancy vaccine and nirsevimab to protect infants against respiratory syncytial virus (RSV) disease. OBJECTIVE: Assess the cost-effectiveness of RSVpreF and nirsevimab programs in preventing RSV disease in infants, compared to a palivizumab program. METHODS: We used a static cohort model of a Canadian birth cohort during their first RSV season to estimate sequential incremental cost-effectiveness ratios (ICERs) in 2023 Canadian dollars per quality-adjusted life year (QALY) for nine strategies implemented over a one-year time period, from the health system and societal perspectives. Sensitivity and scenario analyses were conducted to explore the impact of uncertainties on the results. RESULTS: All-infants nirsevimab programs averted more RSV-related outcomes than year-round RSVpreF programs, with the most RSV cases averted in a seasonal nirsevimab program with catch-up. Assuming list prices for these immunizing agents, all-infants nirsevimab and year-round RSVpreF programs were never cost-effective, with ICERs far exceeding commonly used cost-effectiveness thresholds. Seasonal nirsevimab with catch-up for infants born outside the RSV season was a cost-effective program if prioritized for infants at moderate/high-risk (ICER <$28,000 per QALY) or those living in settings with higher RSV burden and healthcare costs, such as remote communities where transport would be complex (ICER of $5700 per QALY). Using a $50,000 per QALY threshold, an all-infants nirsevimab program could be optimal if nirsevimab is priced at <$110-190 per dose. A year-round RSVpreF for all pregnant women and pregnant people plus nirsevimab for infants at high-risk was optimal if nirsevimab is priced at >$110-190 per dose and RSVpreF priced at <$60-125 per dose. INTERPRETATION: Prophylactic interventions can substantially reduce RSV disease in infants, and more focused nirsevimab programs are the most cost-effective option at current product prices.

Burden of disease of respiratory syncytial virus in infants, young children and pregnant women and people.

Background: Passive immunization products for infants and pregnant women and people have sparked interest in understanding Canada's respiratory syncytial virus (RSV) burden. This rapid review examines RSV burden of disease in infants, young children and pregnant women and people. Methods: Electronic databases were searched to identify studies and systematic reviews reporting data on outpatient visits, hospitalizations, intensive care unit admissions, deaths and preterm labour associated with RSV. We also contacted Canadian respiratory virus surveillance experts for additional data. Results: Overall, 17 studies on infants and young children and 10 studies on pregnant women and people were included, in addition to primary surveillance data from one Canadian territory (Yukon). There were higher rates of medical utilization for infants than older children. Hospitalization rates were highest in infants under six months (more than 1% annually), with 5% needing intensive care unit admission, but mortality was low. Severe outcomes often occurred in healthy full-term infants and burden was higher than influenza. Respiratory syncytial virus attack rate was 10%-13% among pregnant women and people. Only one study found a higher hospitalization rate in pregnant women and people compared to non-pregnant women and people. Limited evidence was found on intensive care unit admission, death and preterm birth for pregnant women and people. Conclusion: While risk of severe outcomes is larger in high-risk infants and children, healthcare burden is greatest in healthy term infants. The RSV severity for pregnant women and people appears to be similar to that for non-pregnant women and people.

Summary of the National Advisory Committee on Immunization (NACI) Rapid Response-Interim guidance on the use of Imvamune in the context of monkeypox outbreaks in Canada.

Background: Monkeypox is endemic in Central and West Africa. Cases in non-endemic countries, including Canada, have been increasing since May 2022. Imvamune®, a live, non-replicating smallpox vaccine, was approved by Health Canada for active immunization against smallpox and monkeypox infections and disease in adults determined to be at high risk for exposure. The aim of this interim guidance is to consider the use of Imvamune for post-exposure prophylaxis (PEP) and to summarize the available evidence in support of Imvamune use in this specific current context. Methods: The National Advisory Committee on Immunization (NACI) High Consequence Infectious Disease Working Group (HCID WG) reviewed data on the current status of the monkeypox outbreak, along with additional evidence included in published scientific literature and from manufacturers, regarding the safety, immunogenicity and protection offered by Imvamune. NACI approved these HCID WG recommendations on June 8, 2022. Results: In brief, NACI recommends that PEP, using a single dose of the Imvamune vaccine, may be offered to individuals with high-risk exposures to a probable or confirmed case of monkeypox, or within a setting where transmission is happening. After 28 days, if an individual is assessed as having a predictable ongoing risk of exposure, a second dose may be offered. Imvamune may be offered to special populations; including individuals who are immunosuppressed, pregnant, breastfeeding, younger than 18 years of age and/or with atopic dermatitis. Conclusion: NACI has rapidly developed guidance on the use of Imvamune in Canada in the context of many uncertainties. Recommendations may be revisited as new evidence emerges.

Summary of the National Advisory Committee on Immunization (NACI) statement update on the recommended use of palivizumab to reduce complications of respiratory syncytial virus infection in infants.

Background: Respiratory syncytial virus (RSV) is the most common cause of lower respiratory tract infection in young children worldwide. Underlying health conditions, especially premature birth, chronic lung disease and congenital heart disease, predispose to severe RSV illness. The only means of prophylaxis against RSV disease is passive prophylaxis with the monoclonal antibody, palivizumab (PVZ) (SynagisTM). The National Advisory Committee on Immunization (NACI) published a statement for PVZ use in 2003. The purpose of this article is to update previous NACI recommendations for the use of PVZ, taking into consideration recent data on RSV burden of illness, effectiveness of PVZ in infants at risk of more severe RSV disease and economic implications of PVZ use. Methods: The NACI Working Group and external experts performed systematic literature reviews on three topics to support updated NACI guidance: 1) RSV burden of disease; 2) PVZ effectiveness; and 3) cost effectiveness of PVZ prophylaxis. Full details and results are presented in the statement and supporting documents. Results: Respiratory syncytial virus hospitalization (RSVH) rates are highest in children younger than one year of age and especially in the first two months of life. In various populations of infants at risk of severe RSV infection, PVZ prophylaxis is associated with reductions of 38%-86% in the risk of RSVH. Only rare cases of anaphylaxis have been reported after decades of use. Palivizumab is expensive and only cost-saving in rare scenarios. Conclusion: Updated NACI recommendations on use of PVZ for the prevention of complications of RSV in infants are now available.

Overview of the respiratory syncytial virus vaccine candidate pipeline in Canada.

A vaccine for respiratory syncytial virus (RSV) has been actively sought for over 60 years due to the health impacts of RSV disease in infants, but currently the only available preventive measure in Canada and elsewhere is limited to passive immunization for high-risk infants and children with a monoclonal antibody. RSV vaccine development has faced many challenges, including vaccine-induced enhancement of RSV disease in infants. Several key developments in the last decade in the fields of cellular immunology and protein structure have led to new products entering late-stage clinical development. As of July 2019, RSV vaccine development is being pursued by 16 organizations in 121 clinical trials. Five technologies dominate the field of RSV vaccine development, four active immunizing agents (live-attenuated, particle-based, subunit-based and vector-based vaccines) and one new passive immunizing agent (monoclonal antibody). Phase 3 clinical trials of vaccine candidates for pregnant women, infants, children and older adults are under way. The next decade will see a dramatic transformation of the RSV prevention landscape.

Gap analyses to assess Canadian readiness for respiratory syncytial virus vaccines: Report from an expert retreat.

Respiratory syncytial virus (RSV) can cause severe disease in infants and older adults. Various vaccine candidates are in development and may become authorized for use in Canada within the next 2-5 years. The Public Health Agency of Canada sought to enhance preparedness for RSV vaccine and passive immunization candidates by organizing an expert retreat to identify knowledge gaps in surveillance and research and development in the context of provincial and territorial RSV public health priorities. We determined that RSV candidate vaccines in development directly address four out of five identified public health priorities, and identified remaining data gaps around vaccine efficacy and effectiveness. We determined that limited or sufficient surveillance data is available to support decision-making for four out of five RSV public health priorities and identified data gaps for several key populations: (i) for RSV cases under 17 years of age, gaps remain for denominator data to calculate incidence and data on medically attended outpatient visits; (ii) for RSV cases in Indigenous and remote communities, gaps remain for data on incidence, prevalence, specific risk factors, feasibility and acceptability; and (iii) for RSV cases in older adults, gaps remain for data on incidence. This process demonstrated the feasibility of, and stakeholder support for, gap analyses in surveillance data to support decisions about prospective vaccines and immune products.

Using the Tools of Informal Science Education to Connect Science and the Public.

Traditional modes of communication within the scientific community, including presentation of data at conferences and in peer-reviewed publications, use technical jargon that limits public engagement. While altering word choice is an important method for increasing public engagement, the data itself may not be enough. For example, communicating the lack of evidence that vaccines cause autism did not convince many reluctant parents to vaccinate their kids (Nyhan, Reifler, Richey, Freed, Pediatrics 133:e835-e842, 2014). To address this gap between the scientific community and the public, many journals are adopting open-access policies and publishing lay-abstracts. Meanwhile, "meet a scientist" programs are creating opportunities for scientists to engage with the public in person. However, these programs may not be as effective as they could be. Many scientists still subscribe to an information-deficit model in which "the data speaks for itself." Alternative tools that go beyond the data are needed. Here, I present three tools to create connections between the public and science: 3-D objects, games, and storytelling. These multidimensional and multisensory methods do more than promote understanding of scientific data; they may also be used to convey science as a verb and as an essential viewpoint in the human struggle for understanding.

Pre-fusion F is absent on the surface of formalin-inactivated respiratory syncytial virus.

The lack of a licensed vaccine for respiratory syncytial virus (RSV) can be partly attributed to regulatory hurdles resulting from vaccine enhanced respiratory disease (ERD) subsequent to natural RSV infection that was observed in clinical trials of formalin-inactivated RSV (FI-RSV) in antigen-naïve infants. To develop an effective vaccine that does not enhance RSV illness, it is important to understand how formalin and heat inactivation affected the antigenicity and immunogenicity of FI-RSV compared to native virus. Informed by atomic structures of RSV fusion (F) glycoprotein in prefusion (pre-F) and postfusion (post-F) conformations, we demonstrate that FI-RSV predominately presents post-F on the virion surface, whereas infectious RSV presents both pre-F and post-F conformations. This significant antigenic distinction has not been previously appreciated. Thus, a stabilized pre-F antigen is more representative of live RSV than F in its post-F conformation, as displayed on the surface of FI-RSV. This finding has major implications for discriminating current pre-F-based immunogens from FI-RSV used in historical vaccine trials.

Prefusion F-specific antibodies determine the magnitude of RSV neutralizing activity in human sera.

Respiratory syncytial virus (RSV) is estimated to claim more lives among infants <1 year old than any other single pathogen, except malaria, and poses a substantial global health burden. Viral entry is mediated by a type I fusion glycoprotein (F) that transitions from a metastable prefusion (pre-F) to a stable postfusion (post-F) trimer. A highly neutralization-sensitive epitope, antigenic site Ø, is found only on pre-F. We determined what fraction of neutralizing (NT) activity in human sera is dependent on antibodies specific for antigenic site Ø or other antigenic sites on F in healthy subjects from ages 7 to 93 years. Adsorption of individual sera with stabilized pre-F protein removed >90% of NT activity and depleted binding antibodies to both F conformations. In contrast, adsorption with post-F removed ~30% of NT activity, and binding antibodies to pre-F were retained. These findings were consistent across all age groups. Protein competition neutralization assays with pre-F mutants in which sites Ø or II were altered to knock out binding of antibodies to the corresponding sites showed that these sites accounted for ~35 and <10% of NT activity, respectively. Binding competition assays with monoclonal antibodies (mAbs) indicated that the amount of site Ø-specific antibodies correlated with NT activity, whereas the magnitude of binding competed by site II mAbs did not correlate with neutralization. Our results indicate that RSV NT activity in human sera is primarily derived from pre-F-specific antibodies, and therefore, inducing or boosting NT activity by vaccination will be facilitated by using pre-F antigens that preserve site Ø.

Structure-based functional characterization of repressor of toxin (Rot), a central regulator of Staphylococcus aureus virulence.

Staphylococcus aureus is responsible for a large number of diverse infections worldwide. In order to support its pathogenic lifestyle, S. aureus has to regulate the expression of virulence factors in a coordinated fashion. One of the central regulators of the S. aureus virulence regulatory networks is the transcription factor repressor of toxin (Rot). Rot plays a key role in regulating S. aureus virulence through activation or repression of promoters that control expression of a large number of critical virulence factors. However, the mechanism by which Rot mediates gene regulation has remained elusive. Here, we have determined the crystal structure of Rot and used this information to probe the contribution made by specific residues to Rot function. Rot was found to form a dimer, with each monomer harboring a winged helix-turn-helix (WHTH) DNA-binding motif. Despite an overall acidic pI, the asymmetric electrostatic charge profile suggests that Rot can orient the WHTH domain to bind DNA. Structure-based site-directed mutagenesis studies demonstrated that R(91), at the tip of the wing, plays an important role in DNA binding, likely through interaction with the minor groove. We also found that Y(66), predicted to bind within the major groove, contributes to Rot interaction with target promoters. Evaluation of Rot binding to different activated and repressed promoters revealed that certain mutations on Rot exhibit promoter-specific effects, suggesting for the first time that Rot differentially interacts with target promoters. This work provides insight into a precise mechanism by which Rot controls virulence factor regulation in S. aureus.

Thermodynamic signatures of the antigen binding site of mAb 447-52D targeting the third variable region of HIV-1 gp120.

The third variable region (V3) of HIV-1 gp120 plays a key role in viral entry into host cells; thus, it is a potential target for vaccine design. Human monoclonal antibody (mAb) 447-52D is one of the most broadly and potently neutralizing anti-V3 mAbs. We further characterized the 447-52D epitope by determining a high-resolution crystal structure of the Fab fragment in complex with a cyclic V3 and interrogated the antigen-antibody interaction by a combination of site-specific mutagenesis, isothermal titration calorimetry (ITC) and neutralization assays. We found that 447-52D's neutralization capability is correlated with its binding affinity and at 25 °C the Gibbs free binding energy is composed of a large enthalpic component and a small favorable entropic component. The large enthalpic contribution is due to (i) an extensive hydrogen bond network, (ii) a π-cation sandwiching the V3 crown apex residue Arg(315), and (iii) a salt bridge between the 447-52D heavy chain residue Asp(H95) and Arg(315). Arg(315) is often harbored by clade B viruses; thus, our data explained why 447-52D preferentially neutralizes clade B viruses. Interrogation of the thermodynamic signatures of residues at the antigen binding interface gives key insights into their contributions in the antigen-antibody interaction.

Structural basis of cyclophilin B binding by the calnexin/calreticulin P-domain.

Little is known about how chaperones in the endoplasmic reticulum are organized into complexes to assist in the proper folding of secreted proteins. One notable exception is the complex of ERp57 and calnexin that functions as part the calnexin cycle to direct disulfide bond formation in N-glycoproteins. Here, we report three new complexes composed of the peptidyl prolyl cis-trans-isomerase cyclophilin B and any of the lectin chaperones: calnexin, calreticulin, or calmegin. The 1.7 Å crystal structure of cyclophilin with the proline-rich P-domain of calmegin reveals that binding is mediated by the same surface that binds ERp57. We used NMR titrations and mutagenesis to measure low micromolar binding of cyclophilin to all three lectin chaperones and identify essential interfacial residues. The immunosuppressant cyclosporin A did not affect complex formation, confirming the functional independence of the P-domain binding and proline isomerization sites of cyclophilin. Our results reveal the P-domain functions as a unique protein-protein interaction domain and implicate a peptidyl prolyl isomerase as a new element in the calnexin cycle.