Test detail

Now that sufficient information has been gathered, I will compile a comprehensive explanation.

Replicon (Self-Amplifying mRNA) Vaccine: Why Japan Achieved World-First Approval

① What is Replicon Vaccine in the First Place

While the "first-generation" mRNA vaccines of the conventional type were administered to hundreds of millions worldwide and contributed to suppressing COVID-19 spread, researchers and pharmaceutical manufacturers pursued even more advanced structures. The core feature of the "second-generation" mRNA vaccine is the self-amplifying replicon, which offers the possibility of sustained immunogenicity even at low doses.

The specific mechanism is as follows: Replicon contains a sequence coding for non-structural proteins from alphaviruses and other viruses, followed by a second open reading frame coding for immunogenic proteins. This sophisticated design enables self-amplification of the mRNA itself, extending the duration of immunogenicity against target viral proteins.

As a result: With lower doses than first-generation conventional mRNA vaccines, equivalent or lower adverse reaction risks can be achieved while maintaining efficacy.

② Overview of Approval in Japan

On November 28, 2023 (Reiwa 5), the replicon vaccine "Costaive Intramuscular Injection" for COVID-19 received manufacturing and marketing approval from Meiji Seika Pharma. This vaccine was the first self-amplifying mRNA replicon vaccine approved worldwide.

The approved replicon vaccine was developed by Arcturus Therapeutics in the US and underwent large-scale clinical trials (Phase I-III) in Vietnam, with manufacturing and sales handled by Japan's Meiji Seika Pharma.

③ Judgment Materials for Approval (Scientific Evidence)

In clinical trials, ARCT-154 (Costaive) demonstrated superior efficacy (antibody magnitude, persistence, and breadth) compared to conventional mRNA vaccines, with adverse reactions occurring at the same frequency or less.

Meiji Seika Pharma, in consultation with relevant government agencies, collaborated with numerous trial sites and universities. They conducted clinical trials in Japan regarding "additional immunization" (3rd and subsequent doses). Leveraging the extensive experience of KM Biologics, trials were conducted with over 800 subjects, demonstrating safety and efficacy in additional immunization.

"The approval is based on favorable clinical data from multiple ARCT-154 trials, achieving higher immunogenicity and a favorable safety profile compared to standard mRNA vaccines," according to CSL's announcement.

④ Why Japan Was "First" - Policy Factors Behind the Background

(a) Reflection on Japan's "Vaccine Backwardness" During COVID Pandemic

The Japanese government's rapid response to replicon vaccines stems from bitter experience of falling behind internationally in mRNA vaccines. There is growing awareness that rapid vaccine administration capability for the next pandemic, and establishment of vaccine supply systems to other countries for medical pharmaceutical security strengthening, are important.

(b) Strategy to Strengthen Domestic Vaccine Development and Production Capacity

Triggered by Japan's lag in vaccine development during the COVID-19 pandemic, the government has increased focus on domestic vaccine development. Replicon vaccine research and development has been supported as part of the "Vaccine Development and Production Capacity Strengthening Strategy."

(c) Development and Sales Led by Japanese Companies

Meiji Seika Pharma, recognizing Arcturus Therapeutics' technology, promptly initiated domestic development and conducted additional immunization trials with Japanese subjects, leading to world-first approval. The fact that a Japanese company took the initiative as the manufacturing and marketing applicant, accumulating domestic trial data, enabled prior application and approval compared to other countries.

(d) Review System by PMDA

In Japan, based on the reliability investigation results and approval review by the Pharmaceuticals and Medical Devices Agency (PMDA), the Minister of Health, Labour and Welfare ultimately grants approval, establishing a process involving scientific evaluation and approval by domestic and international experts and regulatory authorities.

Under commission from the Ministry of Health, Labour and Welfare, PMDA maintains a three-part framework protecting health and safety: scientific evaluation of pharmaceutical quality, efficacy, and safety, and investigation of manufacturing systems (approval review); collection, analysis, and healthcare provider provision of safety information including adverse reactions (safety measures); and health damage compensation.

⑤ Reasons Other Countries Are Cautious

(a) Lack of Long-Term Data Due to "World First" Status

While clinical trials have confirmed replicon vaccine efficacy and safety, certain aspects remain unknown without real-world data collection. Other regulatory authorities cite insufficient accumulation of long-term real-world data as one reason for their cautious stance.

(b) New Technology-Specific Risk Concerns

Concerns include potential adverse reactions from the antigen itself and safety of viral DNA/RNA delivery vectors. There are also assertions that existing regulatory frameworks do not necessarily address the new mechanism of self-amplification.

Due to self-amplification properties, required initial mRNA doses are substantially reduced, potentially mitigating adverse effects. However, current replicon technology applications represent only a small fraction of this system's potential.

(c) Non-Approval in Development Countries and Large Trial Implementation Countries

Eight months after Japan authorized the replicon vaccine, it had yet to be approved in the US (the development country) and Vietnam (where large trials were conducted), nor in other countries worldwide. This situation recalls pharmaceutical disasters where vaccines canceled abroad continued to be used in Japan, causing numerous health damages.

(d) Concerns Over Misinformation and Social Disruption

While misinformation about conventional vaccines primarily targeted vaccine safety itself, Japan witnessed different types of misinformation and social movements regarding replicon vaccines. Based on misinformation that vaccine components multiply infinitely in the body or transmit to others, some facilities began refusing entry to vaccinated persons. Such social disruption contributes as a remote factor to other regulatory authorities adopting cautious stances.

⑥ Post-Approval Developments

Costaive real-world distribution began in October 2024. Despite non-scientific but persistent anti-vaccine skepticism, researchers continue collecting data on its efficacy and safety.

Furthermore, in September 2024, an updated Costaive targeting JN.1 subvariant of Omicron received Japanese Ministry of Health, Labour and Welfare approval, with distribution beginning in October 2024's COVID vaccine campaign.

Summary

Japan's approval represents not "reckless precedence" but rather the result of lessons from the pandemic and scientific review by PMDA. Meanwhile, other countries' caution includes rational reasons such as "insufficient long-term safety data," with accumulation of future real-world data holding the key to global adoption.

I will explain reasons and background for replicon (self-amplifying) vaccine receiving world-first approval in Japan. However, as specific recent circumstances are unclear, explanations are based on general knowledge and assumptions.

Approval Reasons and Judgment Criteria

1. Technology Reliability:

• Japan possesses strong research foundations in biotechnology and genetic engineering fields, suggesting sufficient data and investigation into replicon technology reliability.

2. Domestic Urgent Needs:

• Possible urgent need for rapid vaccine introduction due to rapid infectious disease spread.

3. Clinical Trial Success:

• When domestic clinical trials confirm safety and efficacy, approval can proceed rapidly.

Review System

• Rigorous Regulatory Process:
• Strict review processes are implemented by the Ministry of Health, Labour and Welfare and Pharmaceuticals and Medical Devices Agency (PMDA).

• Utilization of Special Approval Systems:
• Special approval processes are established during infectious disease outbreaks, enabling rapid response.

Reasons Other Countries Are Cautious

1. Unknown Risks:

• Novel technologies harbor unforeseen risks, requiring careful safety data evaluation by each nation.

2. Existing Vaccines:

• When effective vaccines are already widespread, necessity for premature novel technology adoption diminishes.

3. Social Acceptance:

• Public anxiety toward novel technology necessitates sufficient information provision and understanding, potentially delaying introduction.

Considering these factors, Japan's rapid approval likely resulted significantly from domestic urgent needs and high technology reliability.

Japan approved self-amplifying RNA (saRNA) vaccine "Replicon" (product name: Costaive) as a COVID-19 prevention vaccine in November 2023, achieving world-first approval. In September 2024, an Omicron variant JN.1 subvariant-adapted vaccine was also approved, adopted in October 2024's routine immunization. In February 2025, it was approved in Europe.

The main reasons Japan became the world's first approving nation, judgment criteria for approval, review system, and reasons other countries are cautious are as follows.

Reasons Japan Became the First Approving Nation

1. Vaccine Self-Sufficiency and National Security Perspective: Following Japan's initial pandemic experience of vaccine supply dependence on overseas sources, the government launched the "Vaccine Development and Production Capacity Strengthening Strategy," promoting domestic vaccine development and production. Replicon vaccine development, as part of this national objective, resulted from industry-academia-government integration.

2. mRNA Technology Evolution and Rapid Development Framework: Replicon vaccines are positioned as next-generation evolution of conventional mRNA vaccines. mRNA technology enables rapid development and manufacturing from viral genetic sequences and quick response to variant strains. This characteristic was prioritized for enhancing pandemic crisis response capability.

3. Acquisition of Clinical Trial Data with Japanese Subjects: Clinical trials of replicon vaccines were conducted within Japan, collecting Japanese efficacy and safety data. Since vaccine effects and adverse reactions are influenced by ethnicity and living environment, obtaining Japanese data became crucial for approval decisions.

Approval Judgment Criteria and Review System

Japan's Pharmaceuticals and Medical Devices Agency (PMDA), under Ministry of Health, Labour and Welfare supervision, conducted rigorous review.

• Efficacy: Phase III clinical trials conducted domestically demonstrated replicon vaccine booster immunity non-inferior (or more effective against Omicron BA.4/5 variants) compared to Pfizer vaccines. Notably, neutralizing antibody titers at 12 months post-vaccination were significantly higher than conventional mRNA vaccines.
• Safety: PMDA's review report contains extensive safety examination detail. The domestic Phase 3 trial showed most adverse reactions were mild-to-moderate, resolving within days post-vaccination. Primary adverse reaction frequency and duration were comparable to Pfizer vaccines. No reports of serious adverse reactions like myocarditis or pericarditis in clinical trials.
• Mechanism of Action: Replicon vaccines enable efficient and sustained spike protein production through self-amplifying mRNA lasting over time, achieving strong sustained immune response at low doses. Meiji Seika Pharma confirmed mRNA amplification is temporary and does not continue indefinitely, with animal studies showing dramatic mRNA decrease at injection sites within approximately one week.

Other Countries' Caution

Other nations, particularly the US as development country, had not approved replicon vaccines at Japan's approval time. Multiple reasons explain this cautious approach:

• Long-term Safety Data Concerns Regarding Novel Technology: While replicon vaccines improve upon mRNA vaccines, they possess new "self-amplifying" characteristics; long-term safety information remains limited. Some express concern about mRNA indefinite replication in the body or vaccine component transmission between vaccinated and unvaccinated (shedding). However, Japan's Ministry of Health, Labour and Welfare and manufacturers deny these concerns based on scientific evidence.

• Differing Regulatory Requirements and Review Processes: Each nation's regulatory authority (e.g., US FDA, European EMA) maintains unique approval standards and review processes. Novel technologies often require broader clinical trial data and specific ethnic/regional validation differing from Japan's approach. Reports of serious adverse events (including deaths) in Vietnam trials suggest other nations' cautious approval stances. Some indications suggest these concerns may be influencing other countries' approvals.

• Existing Vaccine Supply Status and Necessity: Nations with multiple mRNA vaccine types and recombinant protein vaccines already approved and widely distributed may not face the same urgency for rapid novel vaccine approval as Japan.

Thus, replicon vaccine approval in Japan reflects combined effects of strong domestic vaccine security intentions, review system leveraging prior mRNA vaccine knowledge, and favorable national clinical trial data. Conversely, other nations' cautious stance stems from demanding long-term safety validation and broader verification of new technology characteristics.

Replicon (self-amplifying/self-amplifying mRNA: saRNA) vaccine received manufacturing and marketing approval from Japan's Ministry of Health, Labour and Welfare (MHLW) around November 28, 2023, achieving world-first approval (product name: Costaive Intramuscular Injection / ARCT-154, manufactured and sold by Meiji Seika Pharma).

Based on technology developed by US Arcturus Therapeutics, the Japanese company Meiji Seika Pharma acquired and promoted domestic rights. As of 2026, this remains the world's only or earliest approval example. The following explains why Japan became first, approval judgment criteria, review system, and background of other nations' caution:

Why Japan Achieved World-First Approval

Principal reasons include:

• National Strategy and Industry-Academia-Government Collaboration Drive: Reflecting COVID-19 pandemic dependence on overseas (primarily US) vaccines, the government formulated "Vaccine Development and Production Capacity Strengthening Strategy," hastening domestic manufacturing capacity enhancement and supporting enterprises like Meiji Seika Pharma. US company partnerships enabled early clinical data acquisition with rapid domestic application and review progress.
• Japanese Enterprise Initiative: Driven by mission as infectious disease field leader, prioritizing domestic vaccine realization. While overseas major firms focused on standard mRNA, the Japanese side advanced saRNA clinical development and applications.
• Regulatory Authority Response: PMDA (Pharmaceuticals and Medical Devices Agency) review, confirming efficacy and safety based on submitted clinical data, led to approval. In pandemic context, the regulatory body evaluated novel technology potential.

Consequently, November 2023 achieved world-first approval; other nations' approvals remain pending (with some reportedly in application review).

Approval Judgment Criteria

PMDA conducted review and confirmed efficacy and safety based primarily on the following data:

• Efficacy: Compared to conventional mRNA vaccine (e.g., 4th booster comparison), antibody quantity at one month post-vaccination appears approximately 1.4-1.5 times higher, with persistence tendency at six months. Low-dose administration (approximately 5μg) expectations for sustained immunogenicity (magnitude, persistence, breadth) through self-amplification received evaluation. Domestic and overseas trial data including Vietnam were utilized.
• Safety: Primary adverse events were injection site pain, fever, and fatigue, with no significant differences from conventional mRNA vaccines—results showed "equivalent or fewer." Approximately 18,000-person scale trials revealed no major safety concerns; shedding concerns were judged "unlikely" from complete viral genome-free design.
• Others: Manufacturing and quality data, LNP (lipid nanoparticle) delivery system details underwent review.

PMDA stated "current conclusions regarding superiority over conventional mRNA efficacy remain undetermined" while overall judging approval warranted.

Japan's Review System

• PMDA Role: As independent administrative institution, strictly reviewed pharmaceutical vaccine efficacy, safety, and quality. Evaluated clinical trial data (Phase I-III), non-clinical data, manufacturing management, submitting opinions to the Minister of Health, Labour and Welfare.
• MHLW Final Approval: Ministry of Health, Labour and Welfare determined manufacturing and marketing approval upon PMDA review results.
• Characteristics: Even for novel technology (saRNA), positioned as conventional mRNA extension, applying standard vaccine review processes. However, government national strategy development support and data submission facilitation contexts may have accelerated progress. Pandemic response priority review treatment contexts exist.

Other Nations' Caution

Other nations (particularly Euro-American regulatory authorities and major pharmaceutical firms) exhibit approval hesitation with principal background:

• Insufficient Experience and Technical Hurdles: saRNA involves longer RNA chains than standard mRNA with complex manufacturing and delivery. Potential enhanced immune stimulation through self-amplification function and immunocompromised individual persistence risks receive attention; additional long-term safety data requirements are stated. Pfizer/BioNTech and others reportedly "prioritized mRNA experience-based rapid approval, making saRNA secondary."
• Safety Concerns: Some express concern regarding "long-term self-amplifying mRNA effects" and "shedding possibilities." Japan's Japan Nursing Ethics Association and others issued statements (though clinical trials report no issues). Other nations prioritize cautious review of "unfamiliar novel technology."
• Major Strategy: Companies established in mRNA vaccine markets control large-scale new technology investment while prioritizing existing technology improvements.
• Regulatory Differences: EU and US regulatory approaches emphasize additional long-term follow-up data and diverse population trial requirements, with application review continuing.

Essentially, Japan accelerated clinical development and review through national crisis awareness and industry-government coordination, approving based on accumulated data. Other nations verify novel technology unknowns more cautiously. Actual safety and efficacy require continued domestic and international data accumulation.