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    Self-amplifying RNA (saRNA)

    Also known as saRNA, sa-mRNA, replicon RNA, self-replicating RNA

    Self-amplifying RNA (saRNA) is an RNA vaccine format that encodes viral replication machinery as well as the antigen, so the RNA copies itself inside cells.[1] The first saRNA COVID-19 vaccine, CSL and Arcturus's Kostaive, was marketed in Japan and authorized in the EU in February 2025.[2][3]

    Editor reviewedStrict sourcingUpdated mRNA and next-gen vaccinesHealth and medicineLife sciences
    Key facts

    Self-amplifying RNA (saRNA) is one of the two main types of RNA vaccine studied today. The other is the conventional, non-replicating mRNA used in the first COVID-19 vaccines.[4] It matters because the RNA copies itself inside the cell. That in principle gets more protein, and potentially longer-lasting responses, from each delivered molecule.[1][5]

    How it works

    A conventional mRNA vaccine encodes only the target antigen. A self-amplifying RNA also encodes viral replication machinery, borrowed from viruses. Once inside a cell, this machinery makes more copies of the RNA, which leads to abundant protein expression.[1] CSL describes saRNA vaccines as instructing the body to make more mRNA and protein to strengthen the immune response.[3] For how RNA vaccines are packaged for delivery, see how lipid nanoparticles deliver RNA.

    Most saRNA vaccines start from the genome of an alphavirus. The genes for the virus’s replication machinery are kept, but the genes for its structural proteins, which would let it form new virus particles, are replaced by the vaccine antigen. The resulting RNA is about 9 kilobases long and can be made by in vitro transcription from a DNA template.[6] Because the antigen-encoding RNA replicates inside cells, a very small dose can produce a large amount of antigen.[7] Conventional mRNA vaccines, by contrast, carry only the antigen sequence between untranslated regions, a 5’ cap and a poly(A) tail.[8]

    First approvals

    Kostaive (ARCT-154), developed by CSL and Arcturus Therapeutics, was the first self-amplifying mRNA COVID-19 vaccine. It was marketed in Japan by the time of its EU approval.[2] On 14 February 2025 the European Commission authorized it for adults 18 and older, the first saRNA COVID-19 vaccine approved in the EU.[3]

    Evidence so far

    CSL reported that in a booster study, Kostaive produced superior immunogenicity compared with a conventional mRNA COVID-19 vaccine. It also reported antibody persistence for up to 12 months against several SARS-CoV-2 strains.[5] These are company-reported immunogenicity results, not head-to-head data on hospitalisation or other clinical outcomes. Immunogenicity is a surrogate measure. The US FDA’s biologics centre has argued in another context that antibody levels alone do not establish net clinical benefit.[9]

    Shared foundations with mRNA

    saRNA belongs to the same family of synthetic RNA vaccines as conventional mRNA.[4] For mRNA vaccines, in vitro transcription gives high yields and supports rapid, scalable manufacturing.[10] The same foundational review describes the mRNA platform as non-integrating and degraded by normal cellular processes.[11] Preparedness funders such as CEPI cite fast mRNA authorisation timelines as evidence for platform vaccines.[12]

    Open questions

    As of October 2026, the sources reviewed here do not establish whether saRNA’s amplification translates into better clinical protection than conventional mRNA. They also do not settle whether lower doses lead to fewer side effects. Those questions remain for comparative trials. Developers of conventional mRNA such as Moderna and BioNTech work on the same broad class of RNA vaccine technology.[4]

    This page describes the technology and its regulatory status. It is not medical advice.

    Questions readers ask

    How is self-amplifying RNA different from ordinary mRNA?

    It encodes viral replication machinery as well as the antigen, so the RNA is amplified inside the cell and produces abundant protein.[1]

    Is any self-amplifying RNA vaccine approved?

    Yes. The European Commission authorized CSL and Arcturus's Kostaive COVID-19 vaccine for adults on 14 February 2025, and it was already marketed in Japan.[3][2]

    Does saRNA give longer-lasting antibodies?

    CSL reported that a Kostaive booster produced superior immunogenicity and antibody persistence for up to 12 months compared with a conventional mRNA COVID-19 vaccine.[5]

    Sources

    Each numbered claim is a statement we checked against the sources listed with it. Status shows how well established it is.

    1. [1]

      Self-amplifying RNA encodes both the antigen and viral replication machinery, which lets the RNA copy itself inside the cell and produce abundant protein. confirmedas of 2018-01-12

    2. [2]

      Kostaive was already marketed in Japan for COVID-19 when the EU approved it in February 2025. confirmedas of 2025-02-14

    3. [3]

      On 14 February 2025 the European Commission authorized CSL and Arcturus Therapeutics' Kostaive (ARCT-154), the first self-amplifying mRNA COVID-19 vaccine approved in the EU, for adults 18 and older. confirmedas of 2025-02-14

    4. [4]

      Two major types of RNA are studied as vaccines, non-replicating mRNA and virally derived self-amplifying RNA. confirmedas of 2018-01-12

    5. [5]

      CSL reported that a Kostaive booster produced superior immunogenicity and antibody persistence for up to 12 months compared with a conventional mRNA COVID-19 vaccine. confirmedas of 2025-02-14

    6. [6]

      Most self-amplifying mRNA vaccines are based on an alphavirus genome in which the replication genes are kept but the genes for the virus's structural proteins are replaced by the vaccine antigen; the resulting RNA is about 9 kilobases long. confirmedas of 2018-01-12

    7. [7]

      Because the antigen-encoding RNA replicates inside cells, the self-amplifying platform can produce a large amount of antigen from a very small vaccine dose. confirmedas of 2018-01-12

    8. [8]

      Lab-made (in vitro transcribed) mRNA is built to resemble a mature cellular mRNA, with an open reading frame for the protein flanked by untranslated regions, a 5' cap and a poly(A) tail. confirmedas of 2018-01-12

    9. [9]

      The FDA memo argued that antibody levels are a surrogate endpoint that does not by itself establish net clinical benefit in healthy people. confirmedas of 2025-08-25

    10. [10]

      mRNA vaccines can potentially be manufactured rapidly, cheaply and at scale, mainly because in vitro transcription reactions give high yields. confirmedas of 2018-01-12

    11. [11]

      mRNA is a non-infectious, non-integrating platform that is degraded by normal cellular processes. confirmedas of 2018-01-12

    12. [12]

      CEPI's 2027-2031 strategy notes that the first mRNA COVID-19 vaccine was authorised in just under a year and later strain-updated vaccines in as little as two to three months. confirmedas of 2026-02-01

    13. [13]

      The first authorized mRNA COVID-19 vaccines, Pfizer-BioNTech's BNT162b2 and Moderna's mRNA-1273, both encode the SARS-CoV-2 spike protein and are formulated in lipid nanoparticles. confirmedas of 2023-03-01

    Revision history (2)
    1. Page created.
    2. Added how saRNA constructs are built from alphavirus genomes and why they allow small doses.

    Created Oct 10, 2026. Last reviewed by an editor on Oct 10, 2026. Next scheduled review: Jan 10, 2027.

    Cite this page

    "Self-amplifying RNA (saRNA)." ContentLora, updated Oct 10, 2026. https://contentlora.com/wiki/self-amplifying-rna

    Spotted an error? Suggest a correction or emailcorrections@contentlora.com.

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