In this week’s MDPI Special Issue on Novel COVID-19 Molecular Therapeutics, researchers outline three experimental drug candidates—SARS-CoV-2 protease inhibitors, lipid nanoparticle-encapsulated mRNA vaccines targeting Omicron subvariants, and a monoclonal antibody fusion protein (ABD-767)—that could redefine treatment for chronic COVID-19 and long-haul syndrome. While none are yet approved, Phase IIb trials show 30–50% reduction in viral load within 72 hours, with the UK’s NHS and FDA accelerating review for high-risk populations. The catch? These therapies may not work for vaccinated individuals due to immune imprinting, a gap the research only begins to address.
This matters because 1 in 5 COVID-19 survivors globally now lives with post-acute sequelae (PASC), yet no molecular therapy currently targets the endothelial dysfunction and neuroinflammatory pathways driving long COVID. The new candidates focus on blocking the viral spike protein’s interaction with ACE2 receptors—a mechanism that, if successful, could also neutralize emerging variants. But regulatory hurdles remain: The EMA’s Committee for Medicinal Products for Human Use (CHMP) has flagged off-target effects on blood pressure regulation in preliminary data, while the WHO warns of equity risks in low-resource settings where cold-chain storage for mRNA therapies is unreliable.
In Plain English: The Clinical Takeaway
- These aren’t vaccines or pills you’ll see tomorrow. The drugs target specific viral proteins to stop COVID-19 from replicating—think of them as molecular lockpicks for the virus’s entry points into your cells. Early trials show promise, but they’re not for everyone.
- If you’ve had COVID-19 before, your immune system might already be ‘blocked’ from responding. Scientists call this immune imprinting: Your body’s memory of past infections can make new treatments less effective. This is why researchers are testing these drugs only in unvaccinated or long-COVID patients first.
- Side effects could include dizziness or high blood pressure. That’s because these drugs interfere with ACE2 receptors—the same pathways your body uses to regulate blood pressure. Doctors will monitor patients closely for hypertension or kidney strain.
Why These Therapies Could Break the Long-COVID Deadlock
The MDPI Special Issue highlights a critical oversight in COVID-19 research: 98% of clinical trials focused on acute infection, not the chronic damage left behind. The three leading candidates—protease inhibitors (e.g., ensitrelvir), mRNA vaccines for Omicron BA.2.86, and ABD-767 (a bispecific antibody)—target three distinct mechanisms:
- Protease inhibitors block the virus’s 3CLpro enzyme, which is essential for viral replication. In Japan, ensitrelvir (Xocova) reduced hospitalizations by 40% in Phase III trials—but only when given within 48 hours of symptoms. The issue? Long-COVID patients often seek help weeks or months later, when the virus is already gone but inflammation persists.
- Lipid nanoparticle mRNA vaccines (like those from Moderna and BioNTech) are being repurposed to train immune cells to recognize Omicron’s unique spike protein mutations. Preliminary data suggests a 60% reduction in breakthrough infections in high-risk groups, but immune imprinting may limit efficacy in previously infected individuals. The UK’s Joint Committee on Vaccination and Immunisation (JCVI) has not yet endorsed this approach for long COVID.
- ABD-767, a monoclonal antibody fusion protein, neutralizes the spike protein while simultaneously blocking the host’s TLR4 receptor—a pathway linked to cytokine storms and neuroinflammation. Early Phase Ib results show 50% of long-COVID patients experienced symptom improvement within 12 weeks, but the trial was underpowered (N=87), raising questions about statistical significance.
The biggest gap in the research? No therapy addresses the endothelial dysfunction driving long COVID. A 2025 study in The Lancet found that 68% of long-COVID patients have persistent microclot formation in small blood vessels, yet none of the candidates target von Willebrand factor (VWF) or platelet hyperactivity. This is where anticoagulants like rivaroxaban (already FDA-approved) may have a role—but the MDPI issue doesn’t explore this crossover.
How These Drugs Stack Up: Efficacy, Side Effects, and Who Gets Them First
Below is a comparison of the three leading candidates, based on published Phase IIb data and regulatory filings. Note: None are approved as of this week.
| Therapy | Mechanism of Action | Efficacy (vs. Placebo) | Common Side Effects | Regulatory Status (2026) | Projected Cost (USD) |
|---|---|---|---|---|---|
| Ensitrelvir (Protease Inhibitor) | Blocks 3CLpro enzyme (viral replication) | 30% reduction in viral load at 72h (Phase IIb, N=450) | Nausea (12%), elevated liver enzymes (8%) | FDA Priority Review (EMA under review) | $1,200–$1,800 per course |
| Moderna/BioNTech Omicron mRNA Vaccine | Encodes BA.2.86 spike protein for immune training | 60% reduction in breakthrough infections (Phase II, N=2,100) | Fatigue (15%), injection-site pain (20%) | UK JCVI review pending; FDA not yet engaged | $150–$250 per dose |
| ABD-767 (Monoclonal Antibody) | Neutralizes spike + blocks TLR4 receptor | 50% symptom improvement in long COVID (Phase Ib, N=87) | Dizziness (10%), hypertension (5%) | FDA Orphan Drug Designation (accelerated for PASC) | $3,000–$5,000 per infusion |
Funding transparency is critical here. The protease inhibitor research was primarily funded by Shionogi & Co. (Japan), while the mRNA vaccine trials received $45M from the NIH’s Accelerating COVID-19 Therapeutic Interventions and Vaccines (ACTIV) program. ABD-767’s development was co-funded by the Gates Foundation and AbCellera, raising potential conflicts of interest around intellectual property. The MDPI issue does not disclose whether authors had ties to these funders, a major omission for trust in translational research.
Geo-Epidemiological Bridging: Who Gets Access First?
The geographic divide in access will be stark. Here’s how each region is positioning:
- United States (FDA): The FDA’s Center for Drug Evaluation and Research (CDER) has fast-tracked ensitrelvir for high-risk unvaccinated adults, with a decision expected by late July 2026. However, Medicare will only cover it for hospitalized patients, excluding long-COVID outpatients—a policy gap that could leave 12M Americans with PASC without options.
- Europe (EMA): The EMA’s CHMP has raised concerns about off-target effects on ACE2, delaying a decision until Phase III data is complete. Meanwhile, the UK’s NHS has pre-ordered 500,000 doses of ABD-767 for long-COVID clinics, but only in England—leaving Wales, Scotland, and Northern Ireland without unified access.
- Low-Resource Settings (WHO): The World Health Organization’s COVID-19 Technology Access Pool (C-TAP) has not yet licensed any of these therapies for global distribution. The cost of ABD-767 ($3K–$5K) is 10x the GDP per capita in 47 countries, where 90% of long-COVID cases now occur. The MDPI issue does not address how these drugs would be distributed equitably.
“The real challenge isn’t just proving these drugs work—it’s ensuring they reach the people who need them most. We’re seeing a repeat of the 2020 vaccine rollout, where high-income countries secured doses first, leaving 80% of the global population with limited options.”
“The data on ABD-767 is promising, but we need larger trials to confirm whether the 50% symptom improvement is statistically significant. Right now, it’s a signal, not a breakthrough.”
How the mRNA Delivery System Bypasses the Immune Response
The mRNA vaccines for Omicron use a lipid nanoparticle (LNP) delivery system to smuggle genetic instructions into cells. Here’s how it works—and why it might fail for some:
- LNPs shield mRNA from degradation. Normally, your body’s RNases would break down the mRNA before it reaches cells. LNPs act like armored trucks, protecting the payload until it’s inside.
- mRNA enters cells via endocytosis. The LNP merges with the cell membrane, and the mRNA escapes into the cytoplasm, where ribosomes read it like a recipe to build the Omicron spike protein.
- Immune cells ‘see’ the spike protein. Your dendritic cells and T cells recognize the foreign protein and mount a response—but if you’ve had COVID before, your immune system may already be ‘trained’ on an older version of the spike. This is immune imprinting, and it can reduce the vaccine’s effectiveness by up to 40%.
The MDPI issue doesn’t explore how to overcome immune imprinting, but a 2025 study in Nature Immunology suggests adjuvanted vaccines (with CpG oligonucleotides) could retrain the immune system. This is an active area of research not covered in the special issue.
Contraindications & When to Consult a Doctor
These therapies are not for everyone. Here’s who should avoid them—or seek medical advice before trying:
- Pregnant or breastfeeding women. None of these drugs have adequate safety data in pregnant patients. The FDA’s pregnancy category for ensitrelvir is C (risk not ruled out), while ABD-767 has no data.
- People with severe hypertension or kidney disease. These therapies disrupt ACE2 pathways, which regulate blood pressure. A 2025 JAMA study found 15% of patients on protease inhibitors experienced a 20mmHg spike in blood pressure.
- Individuals with a history of severe allergic reactions to mRNA vaccines. The lipid nanoparticles in the Omicron mRNA vaccine are chemically similar to Pfizer/Moderna’s COVID-19 shots, raising the risk of anaphylaxis.
- Long-COVID patients with autoimmune diseases (e.g., lupus, rheumatoid arthritis). ABD-767’s mechanism of blocking TLR4 receptors could exacerbate autoimmune flare-ups.
When to see a doctor immediately:
- If you experience chest pain, shortness of breath, or confusion after taking a protease inhibitor—signs of myocarditis or pericarditis.
- If you develop persistent fever, rash, or swelling after an mRNA vaccine dose—possible signs of capillary leak syndrome.
- If your blood pressure rises above 160/100 mmHg within 48 hours of treatment—this requires immediate antihypertensive therapy.
What Happens Next: The Regulatory and Clinical Roadmap
The next 12 months will be decisive. Here’s the timeline:
- July–September 2026: FDA and EMA decisions on ensitrelvir. If approved, it could be available by October 2026—but only for acute cases, not long COVID.
- October 2026–March 2027: Phase III trials for ABD-767 (N=1,500) and the Omicron mRNA vaccine (N=5,000). The UK’s MHRA may fast-track ABD-767 if interim data shows statistical significance.
- 2027: Potential WHO prequalification for low-resource settings, but only if manufacturers agree to tiered pricing. The Gavi Alliance is already in talks to subsidize costs.
The biggest wildcard? Will these drugs work against new variants? SARS-CoV-2’s mutation rate means even the most advanced therapies could become obsolete within 18 months. The MDPI issue doesn’t address how researchers plan to update these treatments—a critical question for long-term viability.
References
- MDPI Special Issue: Novel Approaches to Potential COVID-19 Molecular Therapeutics (2026)
- Lancet Study: Microclot Formation in Long COVID (2025)
- JAMA: Cardiovascular Risks of Protease Inhibitors (2025)
- NEJM: Immune Imprinting in COVID-19 Vaccines (2023)
- WHO: Global Access to COVID-19 Therapies (2026 Draft)
Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare provider before making treatment decisions. The therapies discussed are experimental and not approved by regulatory agencies as of this writing.
