Preventive therapeutics increasingly include long-acting mAbs, extended-duration HIV prophylaxis, RNA medicines, and microbiome interventions, alongside conventional vaccines.
Long duration can be created through Fc engineering, sustained-release formulations, targeted oligonucleotide delivery, or persistent changes to microbial populations, making product design and manufacturing central to preventive performance.
In long-acting products, durability creates additional development considerations because drug exposure can persist after scheduled treatment stops and may not be readily reversible.
RNA therapeutics illustrate the distinction between durable modification of a disease-associated risk factor and demonstrated prevention of clinical events.
As preventive modalities diversify, developers increasingly need to align molecular design, formulation, analytical strategy, manufacturing, and clinical objectives around a defined period of protection.
Prevention Is Becoming a Broader Pharmaceutical Design Objective
Prevention has long been associated most closely with vaccination, particularly in infectious disease. However, a wider range of pharmaceutical technologies is increasingly being developed and deployed before disease occurs, before an infection is acquired, or after treatment to reduce the likelihood of recurrence. These approaches work through very different mechanisms. Some provide passive immunity. Others maintain pharmacologically active drug concentrations over long periods, durably alter expression of biological targets associated with future disease risk, or help restore a microbial environment disrupted by prior disease and treatment.
Several recent and emerging products illustrate how diverse this landscape has become. The long-acting monoclonal antibodies (mAbs) nirsevimab and clesrovimab provide protection against respiratory syncytial virus (RSV) with a single administration intended to cover an infant through an RSV season.1–4 Human immunodeficiency virus (HIV) pre-exposure prophylaxis (PrEP) has progressed from daily oral medicines to long-acting cabotegravir administered every two months and lenacapavir administered every 26 weeks.5–9 Small interfering RNA (siRNA) medicines have demonstrated sustained modification of cardiovascular risk factors with maintenance dosing measured in months. Microbiota-based products are now approved specifically to prevent recurrent infection (CDI) following antibacterial treatment.
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Clostridioides difficile
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These products do not constitute a single therapeutic class, nor do they represent substitutes for vaccines as a category. What connects them is the objective around which they are designed. A preventive therapeutic must establish an appropriate biological state before the event it is intended to prevent and preserve sufficient activity through the relevant period of risk. That places unusual emphasis on duration, delivery, molecular and formulation design, product consistency, and the consequences of interventions that may remain active long after administration.
Designing Passive Immunity to Last
Long-acting antibodies provide one of the clearest demonstrations of how an established therapeutic modality can be engineered around a preventive product profile. Rather than stimulating the immune system to generate its own protective response, a mAb can supply a defined antibody directly. For that strategy to function as practical prophylaxis, sufficient antibody exposure must persist through the period when protection is needed.
Nirsevimab demonstrates the model in RSV prevention. In the phase III MELODY trial, healthy late-preterm and term infants received a single intramuscular dose before or during their first RSV season. Medically attended RSV lower respiratory tract infection through 150 days occurred in 1.2% of infants receiving nirsevimab and 5.0% receiving placebo, corresponding to an efficacy of 74.5%.1 The U.S. Food and Drug Administration (FDA) subsequently approved nirsevimab for prevention of RSV lower respiratory tract disease in neonates and infants born during or entering their first RSV season, as well as certain children who remain vulnerable through their second season.2
The product’s duration is linked directly to molecular engineering. Nirsevimab contains a three-amino-acid YTE substitution in the fragment crystallizable (Fc) region designed to increase interaction with the neonatal Fc receptor (FcRn) and prolong terminal half-life.14 The modification helps a single antibody administration maintain sufficient exposure across a risk period measured in months rather than requiring frequent repeat dosing.
Clesrovimab reinforces the idea that extended-duration RSV antibody prophylaxis can be achieved through more than one molecule. The FDA approved clesrovimab in 2025 for prevention of RSV lower respiratory tract disease in neonates and infants born during or entering their first RSV season.4 In its pivotal trial, a single dose reduced RSV-associated medically attended lower respiratory infection by approximately 60% and RSV-associated hospitalization by approximately 84% through 150 days compared with placebo.3,4 Clesrovimab also incorporates Fc modification to extend serum half-life.15
For developers, the implications extend beyond pharmacokinetics. Increasing FcRn binding is an established strategy for extending antibody circulation half-life, but Fc mutations can alter other molecular properties relevant to developability. In one comparative analysis, YTE engineering reduced thermal stability and increased aggregation propensity in the antibody tested, in addition to altering other Fc interactions.16 Those findings do not mean that every YTE-containing antibody will exhibit the same liabilities, but they illustrate why half-life extension cannot be evaluated as an isolated molecular optimization.
When persistence is central to the preventive product profile, developability has to be considered alongside pharmacokinetic performance. An Fc modification that extends protection may also influence stability, aggregation behavior, purification performance, or other attributes that affect whether the molecule can become a robust manufactured product.16 Prevention expands the development question beyond whether an antibody binds the right target. The molecule also has to remain active, sufficiently stable, and manufacturable for the period in which protection is expected.
Duration Alone Is Not Enough
The potential for antibody-based prevention extends beyond RSV. Malaria trials have demonstrated that a single mAb administration can provide meaningful protection through an entire transmission season. In a phase II study conducted in Mali, one intravenous dose of CIS43LS produced efficacy of 75.0% or 88.2% against Plasmodium falciparum infection over six months, depending on dose.17 A later study in children evaluated the mAb L9LS by subcutaneous administration and reported efficacy of 66% to 70% against infection and 67% to 77% against clinical malaria through six months, again depending on dose.18
The progression also underscores that half-life is only one element of a preventive product profile. Dose and route influence how an intervention can be deployed in its intended population, and a molecule capable of prolonged exposure may still require substantial development to translate that pharmacology into a practical administration strategy.
Antibody prophylaxis also reveals another constraint: persistent exposure is useful only when the molecule remains active against the biological targets encountered during the protection period. Two randomized trials evaluating the broadly neutralizing HIV antibody VRC01 did not demonstrate significant prevention of HIV acquisition overall. Protection was substantially greater, however, against viral isolates that were sufficiently sensitive to the antibody.19
For preventive antibodies, pharmacokinetic durability and biological breadth therefore address separate requirements. The first determines whether enough antibody remains in circulation. The second determines whether that antibody remains relevant to the variants or strains encountered while it is present. A long-lived product with insufficient breadth may maintain exposure without maintaining adequate protection.
Antibody-based pre-exposure prophylaxis also remains relevant in specific contemporary settings, including the current emergency use authorization for pemivibart in certain moderately to severely immunocompromised individuals.20 Across these applications, molecular persistence is only part of the problem. Target selection, breadth, route, and the anticipated biological environment all help determine whether long antibody exposure translates into useful prophylaxis.
From Daily Prevention to Months of Persistent Drug Exposure
Antibodies are not the only modality in which preventive development is increasingly organized around duration. HIV PrEP provides a particularly clear progression from repeated self-administration toward sustained pharmacologic exposure.
The FDA approved injectable cabotegravir for HIV PrEP in 2021, with maintenance injections administered every two months.5 In HPTN 083, long-acting cabotegravir was superior to daily oral tenofovir disoproxil fumarate–emtricitabine for prevention of incident HIV infection in the population studied.6 The mechanism remains pharmacologic rather than immunologic, but the product changes how frequently the individual must act to maintain protection.
Lenacapavir extends that interval considerably further. In PURPOSE 1, no HIV infections occurred among 2,134 initially HIV-negative participants assigned to twice-yearly subcutaneous lenacapavir.7 PURPOSE 2 recorded two HIV infections among participants receiving lenacapavir, with incidence significantly below both estimated background incidence and incidence with the daily oral comparator.8 The FDA has since approved lenacapavir for HIV PrEP as Yeztugo, using a continuation regimen of 927 mg delivered as two 1.5-mL subcutaneous injections every 26 weeks.9
The progression from daily oral dosing to administration every two months and then every six months demonstrates how dosing interval can become a defining feature of a preventive product. It does not eliminate adherence requirements. It changes their form. With a twice-yearly product, maintaining protection depends less on daily tablets and more on receiving scheduled injections and completing associated testing at the appropriate times. FDA specifically warns that missed Yeztugo doses or HIV acquisition during or after use can contribute to development of lenacapavir resistance.9
Reaching a six-month interval also shifts attention toward the dosage form itself. Sustained exposure must arise from the properties of the molecule, the formulation, or their interaction.
Long Acting Is a Formulation Strategy, Not Simply a Dosing Schedule
Long-acting injectable medicines can use several approaches to sustain drug release, including poorly soluble crystalline suspensions, polymeric microspheres, in situ forming systems, and solution formulations that create depots after administration.21 For crystalline suspensions, particle size and particle-size distribution can influence dissolution and therefore the rate at which active drug becomes available. The exposure profile can consequently depend on characteristics created and controlled through formulation and manufacturing.
Lenacapavir provides an instructive example of a different strategy. Its subcutaneous injectable formulation contains lenacapavir at 309 mg/mL in a polyethylene glycol 300 and water vehicle.9 Published formulation work describes precipitation of lenacapavir after subcutaneous administration as solvent diffuses away from the injection site, creating a depot from which dissolution limits subsequent drug release.21 The extended dosing interval therefore reflects more than the intrinsic potency of the active molecule. It depends on a dosage form designed to translate that potency into persistent exposure.
Release behavior becomes a critical quality consideration because formulation characteristics can influence the pharmacokinetic profile that underlies protection. Particle characteristics, depot formation, drug solubility, injection volume, and administration route can all interact with the desired release pattern.21 Understanding those relationships is important for linking reproducible manufacturing to reproducible product performance over an extended dosing interval.
In this sense, duration is partly manufactured. The molecule establishes what pharmacology is possible, while formulation design and process control help determine how that pharmacology unfolds over time.
Durability Creates Its Own Risks
The advantages of long exposure are accompanied by a less intuitive development problem: once a long-acting preventive has been administered, its activity may be difficult to stop.
FDA guidance for development of systemic HIV PrEP specifically identifies this issue for long-acting products. Some formulations may not be removable after administration, making it impossible to withdraw the drug promptly if an adverse reaction occurs. The FDA therefore recommends characterizing the complete systemic concentration-time course after the final dose, including residual concentrations that persist after regular dosing stops.22
Those residual concentrations can have consequences beyond tolerability. In anti-infective prevention, declining drug exposure may create a period in which concentrations remain biologically active but are no longer fully protective. The FDA identifies potential effects on safety, resistance, and drug interactions as considerations that need to be understood across this pharmacokinetic tail.
Lenacapavir makes the issue concrete. The FDA states that residual systemic concentrations can remain for 12 months or longer after the last subcutaneous dose.9 The prescribing information therefore emphasizes continued HIV testing and appropriate alternative prevention if the product is discontinued.
Durability has a dual character in preventive drug development. It can reduce administration frequency while extending the period during which the consequences of a dose must be understood and managed. Product characterization therefore has to account for the full exposure profile, including what occurs after scheduled dosing ends.
Long-acting antibodies and HIV PrEP largely prevent an external pathogen from establishing clinically consequential infection. RNA therapeutics open another possibility: sustained intervention against endogenous biological factors associated with future disease.
Inclisiran provides an established example of durable RNA pharmacology. The siRNA inhibits hepatic synthesis of proprotein convertase subtilisin/kexin type 9 (PCSK9). In the phase III ORION-10 and ORION-11 trials, inclisiran was administered on day 1, again at day 90, and then every six months. Placebo-adjusted reductions in low-density lipoprotein cholesterol (LDL-C) were approximately 50%.10
The distinction between risk-factor modification and prevention of clinical events is important. The ORION trials establish sustained LDL-C lowering with infrequent administration, but those data alone do not establish cardiovascular-event prevention.10 Durable modification of a risk factor can provide the biological premise for prevention, while outcome studies determine whether changing that factor ultimately reduces the events that matter clinically.
Olpasiran illustrates that evidentiary progression. The investigational siRNA reduces hepatic production associated with lipoprotein(a), or Lp(a), and phase II evaluation demonstrated substantial lowering of circulating Lp(a).11 The ongoing phase III OCEAN(a)-Outcomes study is designed to test whether that reduction translates into fewer cardiovascular events, including coronary heart disease death, myocardial infarction, and urgent coronary revascularization.23
RNA interference therefore extends the preventive concept beyond maintaining a defensive molecule against an external exposure. It can instead maintain a modified internal biological state over time. The preventive hypothesis becomes that sustained alteration of a relevant pathway will reduce the probability of a future clinical event, with durable target modulation and demonstrated clinical benefit representing separate evidentiary steps.
For RNA Therapeutics, Delivery and Chemistry Are Part of the Medicine
The prolonged activity associated with some siRNA medicines cannot be separated from how the oligonucleotide reaches its intended tissue. N-acetylgalactosamine (GalNAc) conjugation is an established strategy for directing siRNAs and antisense oligonucleotides to hepatocytes through the asialoglycoprotein receptor, and inclisiran is among the GalNAc-conjugated products developed using this approach.24
Delivery chemistry is therefore part of the therapeutic architecture rather than a late formulation choice. Sequence, chemical modification, conjugate, and tissue targeting work together to determine where the molecule acts and whether sufficient activity persists at the intended site.24 For applications built around infrequent administration, the delivery strategy contributes directly to the product profile.
Manufacturing introduces a different set of constraints. Conventional therapeutic oligonucleotide production commonly includes solid-supported synthesis, cleavage and deprotection, purification, and isolation.25,26 Solid-phase phosphoramidite chemistry remains a principal manufacturing approach, but iterative synthesis creates a complex impurity profile. Shorter sequences, longer sequences, and other undesired species can arise from incomplete or unintended chemical reactions, making purification and analytical control central to establishing drug-substance quality. Longer sequences add further synthetic operations and additional opportunities for impurity formation.26
Established processes can also consume substantial quantities of solvents and reagents across synthesis, purification, and isolation, creating material-efficiency and sustainability considerations as the modality expands.25 Regulatory attention reflects the modality’s distinctive development profile. The European Medicines Agency’s (EMA) current draft guideline on oligonucleotides addresses manufacturing processes, characterization, specifications, analytical control, conjugation, and drug product development, while the FDA’s final guidance on clinical pharmacology identifies considerations including immunogenicity, hepatic and renal impairment, QTc assessment, and drug interactions.27,28
The preventive promise of infrequent RNA dosing therefore rests on a platform with highly specific delivery, synthetic chemistry, purification, and analytical requirements. The biological target defines what the medicine is intended to change, but the oligonucleotide platform determines whether that change can be produced reproducibly and maintained over the intended interval.
Microbiome Therapeutics Introduce a Different Kind of Prevention
Microbiome therapeutics approach prevention from another direction. Instead of supplying a protective antibody, maintaining an antiviral concentration, or suppressing expression of a molecular target, they can reshape a microbial environment associated with recurrence.
Recurrent CDI provides the most established example. In the phase III ECOSPOR III trial, recurrent infection through eight weeks occurred in 12% of patients receiving SER-109 compared with 40% receiving placebo.29 The FDA subsequently approved the product as VOWSTTM for prevention of recurrent CDI in adults following antibacterial treatment for recurrent disease. In the data set described by the FDA, recurrence through eight weeks occurred in 12.4% of VOWST recipients and 39.8% of placebo recipients.12
Rebyota provides a second approved microbiota-based approach to the same preventive objective. The FDA indicates the product for prevention of recurrent CDI in adults following antibiotic treatment for recurrent infection.13 In the PUNCH CD3 phase III trial, the model-estimated treatment-success rate at eight weeks was 70.6% with RBX2660 and 57.5% with placebo. More than 90% of participants who achieved treatment success at eight weeks maintained that response through six months in both groups.30
These products establish a specific, clinically validated form of microbiome prevention: reducing the likelihood that CDI will recur after antibacterial treatment. They do not establish that manipulating the microbiome can broadly prevent unrelated diseases. Their significance lies in demonstrating that a therapeutic can intervene in recurrence by supporting restoration of a microbial environment disrupted by infection and antibiotic exposure. The FDA describes fecal microbiota administration as being thought to facilitate restoration of gut flora as part of this therapeutic rationale.12
That strategy changes what constitutes the active therapeutic system. Instead of a single molecular species whose identity and concentration define much of the product, a microbiome therapeutic may contain complex biological material whose identity, viability, provenance, and unwanted components all require control.
From Biological Complexity to Defined Consortia
FDA guidance for live biotherapeutic products (LBPs) illustrates the quality questions created by living therapeutic systems. The agency defines an LBP, for purposes of the guidance, as a biological product containing live organisms that is applicable to the prevention, treatment, or cure of disease and is not a vaccine.31 Recommended chemistry, manufacturing, and controls (CMC) information includes organism identity and strain designation, original cell source, culture and passage history, phenotype and genotype, raw-material controls, and stability.31
Identity requires unusual resolution compared with many conventional drugs. The FDA recommends identifying organisms to both the species and strain level using at least two complementary methods. The guidance also calls for evaluation of antibiotic susceptibility and, where relevant, whether antibiotic-resistance traits can transfer to other microorganisms. Mechanistic understanding can also help support development of quality criteria and potency-indicating assays.
VOWST shows how these issues translate into commercial manufacturing for a donor-derived microbiota product. It is manufactured from human fecal material obtained from qualified donors whose donations undergo testing for transmissible pathogens.32 Manufacturing enriches bacterial spores by treating fecal material with ethanol to kill non-spore organisms, followed by filtration to remove solids and residual ethanol. Each capsule is manufactured to contain a specified range of viable Firmicutes spore colony-forming units.
Source qualification consequently becomes part of product control. The FDA’s regulatory review describes donor qualification using questionnaires, physical examinations, and blood and stool pathogen testing.33 The review also documents deficiencies involving potency-assay validation and donor-screening assays that were addressed during development, alongside evaluation of manufacturing consistency, specifications, and stability. The agency ultimately concluded that the submitted chemistry, manufacturing, and controls information supported consistent manufacturing and product quality.
Some complexity remains inseparable from the product. VOWST’s prescribing information warns that because the product is manufactured from human fecal material, there is a potential risk of transmitting infectious agents.32 Manufacturing control therefore extends beyond the intended microbial components to the provenance of the starting material and the exclusion of unwanted biological agents.
Defined microbial consortia offer a different starting point. VE303 consists of eight well-characterized, nonpathogenic, nontoxigenic commensal Clostridia strains. Although the strains were originally isolated from healthy human stool, they are manufactured from clonal cell banks rather than repeatedly sourced from new donor material. In a phase II study, recurrent CDI through week 8 using the broadest prespecified definition occurred in 13.8% of participants receiving high-dose VE303, 37.0% receiving the lower dose, and 45.5% receiving placebo.34
VE303 has since advanced into a randomized phase III prevention study, with the current trial record describing eight clonally derived strains manufactured under good manufacturing practice conditions.35 A defined consortium does not make microbiome manufacturing simple. Strain identity, viability, composition, potency, stability, and interactions among living organisms still require control. However, it illustrates a potential progression from repeated reliance on donor-derived starting material toward defined microbial populations that can be propagated from controlled banks.
Different Modalities Create Different Definitions of Control
Across preventive modalities, the shared development challenge is not merely how to make an intervention last. It is how to identify and control the attributes that determine whether the intended protective profile is reproduced from dose to dose and batch to batch.
For engineered antibodies, persistence may be linked to molecular modifications that also affect stability, aggregation, and other developability attributes.16 The relevant control strategy therefore must account for a molecule whose pharmacokinetic advantage may be connected to changes elsewhere in its physical or functional profile.
For long-acting injectables, the dosage form can govern how quickly drug becomes available over weeks or months. Particle characteristics, dissolution behavior, or depot formation may therefore have direct consequences for release and exposure.21 Manufacturing consistency is meaningful only if consistent material also produces sufficiently consistent performance over the intended dosing interval.
Oligonucleotides create another definition of control. Sequence identity, conjugation, product-related impurities, purification, and analytical characterization all contribute to the quality of a chemically synthesized therapeutic whose delivery system is integrated into the molecule itself.24,26,27
Microbiome therapeutics extend control into living systems. Depending on the product, relevant attributes can include strain identity, viable content, source qualification, pathogen exclusion, potency, and stability.31,33 Moving toward defined consortia may change the starting material and some elements of the control strategy, but it does not remove the need to characterize biological complexity.
Long-acting products add another consideration because the end of scheduled dosing may not coincide with the end of pharmacologic activity. In anti-infective prevention, residual exposure can remain relevant to safety and resistance after treatment stops.22 The specific assays and critical quality attributes differ across modalities, but each platform requires developers to understand which product characteristics govern the intended preventive performance and how reliably those characteristics can be reproduced.
Designing Medicines Around a Future Event
Preventive therapeutics are distinguished by the fact that their desired outcome lies ahead of administration. The intervention may be intended to protect an infant through a future RSV season, maintain HIV prophylaxis between injections, reduce the likelihood of recurrent CDI after antibiotic treatment, or alter a cardiovascular risk factor in anticipation of events that might otherwise occur later.
That future orientation places time near the center of the target product profile. Developers have to define the event they are trying to prevent, determine when and for how long the relevant population is at risk, establish what biological or pharmacologic condition needs to be maintained, and understand what happens as the intervention’s effect declines.
The answers are highly modality specific. An RSV antibody may require the right target, sufficient breadth, Fc engineering, and a dose capable of sustaining protection across a season. A long-acting HIV PrEP injection adds formulation-driven release, dosing logistics, a prolonged pharmacokinetic tail, and resistance risk if the dosing schedule is interrupted. A liver-directed siRNA integrates target biology with chemical modification, tissue-specific conjugation, iterative synthesis, purification, and impurity control. A microbiome product must translate a desired ecological effect into a living product that can be sufficiently identified, characterized, and reproduced.
These considerations argue for earlier integration of disciplines that can sometimes be treated sequentially during drug development. Molecular design determines what type of persistence is possible. Formulation and delivery determine how that potential is expressed in the patient. Analytical methods establish whether the attributes responsible for performance remain controlled, while manufacturing determines whether those attributes can be reproduced reliably. For preventive products built around extended duration, these decisions converge on a common objective: creating a product whose performance matches the period in which protection is needed.
Prevention Beyond Vaccines Will Not Be One Technology
The emerging preventive landscape does not point toward a single dominant platform. Its significance lies in the growing number of ways developers can create protection before an unwanted clinical event occurs.
That diversity places greater importance on defining the temporal dimensions of the product early. The intended duration of protection, the mechanism that creates it, the attributes that manufacturing must control, and the consequences of residual activity all become part of the same development problem.
The challenge is increasingly integrative. Molecular design, formulation, delivery, analytics, manufacturing, and clinical strategy must converge on a product that can produce the intended preventive effect reliably in the population for which it was designed. As preventive therapeutics expand beyond vaccines, the central question will be not simply how long an intervention can last, but whether developers can translate that persistence into a reproducible, well-characterized, and clinically meaningful period of protection.
6. Landovitz, Raphael J, et al. “Cabotegravir for HIV Prevention in Cisgender Men and Transgender Women.” New England Journal of Medicine. 385: 595–608 (2021). https://pubmed.ncbi.nlm.nih.gov/34379922/
32. “VOWST (fecal microbiota spores, live-brpk) Capsules, for Oral Administration. Prescribing Information.” U.S. Food and Drug Administration. Apr. 2023. https://www.fda.gov/media/167579/download
