U.K. Approves sa-mRNA COVID-19 Vaccine 'Kostaive'

Injection forces body to make spike protein plus an enzyme that makes copies of the vaccine samRNA.

Source: Jon Fleetwood, SUBSTACK, January 3, 2026

The UK’s Medicines and Healthcare products Regulatory Agency (MHRA) on Saturday approved Arcturus Therapeutics’s Kostaive (zapomeran, ARCT-154) self-amplifying sa-mRNA COVID-19 vaccine for individuals aged 18 years and older.

Governments are not only ignoring concerns about mRNA injections but are authorizing enhanced versions of these genetic products despite limited long-term safety data and unresolved questions about duration, biodistribution, and immune effects.

ARCT-154 delivers a single self-replicating mRNA molecule that encodes both the SARS-CoV-2 spike protein and an alphaviral replicase enzyme.

The sa-mRNA is said to be derived from a Venezuelan equine encephalitis virus (VEEV).

The mRNA is then translated by human cells to first produce the replicase enzyme, which then amplifies copies of the entire mRNA payload in the cytoplasm.

In other words, after injection, the body will produce both the COVID spike protein as well as an enzyme that makes more copies of the samRNA.

U.K. Approves Self-replicating sa-mRNA COVID-19 Vaccine 'Kostaive'- 3 — Non-replicating mRNA (NRM) constructs encode the coding sequence (CDS), and are flanked by 5′ and 3′ untranslated regions (UTRs), a 5′-cap structure and a 3′-poly-(A) tail. The self-amplifying mRNA (SAM) construct encodes additional replicase components able to direct intracellular mRNA amplification. (1) NRM and SAM are formulated in this illustration in lipid nanoparticles (LNPs) that encapsulate the mRNA constructs to protect them from degradation and promote cellular uptake. (2) Cellular uptake of the mRNA with its delivery system typically exploits membrane-derived endocytic pathways. (3) Endosomal escape allows release of the mRNA into the cytosol. (4) Cytosol-located NRM constructs are immediately translated by ribosomes to produce the protein of interest, which undergoes subsequent post-translational modification. (5) SAM constructs can also be immediately translated by ribosomes to produce the replicase machinery necessary for self-amplification of the mRNA. (6) Self-amplified mRNA constructs are translated by ribosomes to produce the protein of interest, which undergoes subsequent post-translational modification. (7) The expressed proteins of interest are generated as secreted, trans-membrane, or intracellular protein. (8) The innate and adaptive immune responses detect the protein of interest. (Jackson, N.A.C., Kester, K.E., Casimiro, D. et al. The promise of mRNA vaccines: a biotech and industrial perspective. npj Vaccines 5, 11 (2020). https://doi.org/10.1038/s41541-020-015.) Licensed under the Creative Commons Attribution 4.0 International license (Wikimedia Commons).

An MHRA press release reads:

The Medicines and Healthcare products Regulatory Agency (MHRA) has today, 2 January 2026, approved zapomeran (Kostaive) mRNA COVID-19 vaccine, for the immunisation of individuals aged 18 years of age and older.
Zapomeran is given as a single 0.5 mL booster dose by injection into the muscle of the upper arm. It contains a self-amplifying messenger RNA (sa-mRNA) which instructs the body’s cells to temporarily make the SARS-CoV-2 spike protein. This teaches the immune system to fight off the virus in the future.