The present invention relates to compositions comprising RNA, preferably messenger RNA (mRNA), more preferably self-amplifying RNA (saRNA), and polymers, in particular cationic polymers, such as polyethylenimine (PEI), poly-L-Lysin (PEL), polyvinylamine (PVA) or polyallylamine (PAA), where individual RNA molecules are present in solution. In the formulations, the RNA is preferentially present in the form of monomers, dimers, timers or oligomers, but not as aggregates comprising a large number of RNA molecules per aggregate, in particular large polyplex nanoparticles. The formulations display improved transfection efficacy and they can be used for delivery of RNA to a subject, where they have an improved dose response relationship in comparison to formulations where large aggregates in the form of polyplex nanoparticles are present.