The disclosure relates to a composition comprising an RNA molecule complexed with a particle of a cationic oil-in-water emulsion, wherein the particle comprises (a) an oil core that is in liquid phase at 25 &ring；C, and (b) a cationic lipid, and wherein the RNA molecule encodes a polypeptide antigen and the RNA is attached to the surface of the particle by non-convalent interactions. The emulsion particles comprise an oil core and a cationic lipid selected from the group consisting of: 1,2-dioleoyloxy-3-(trimethylammonio)propane (DOTAP), 3(-[N-(N&rsquo；,N&rsquo；-Dimethylaminoethane)-carbamoyl] Cholesterol (DC Cholesterol), dimethyldioctadecylammonium (DDA), 1,2-Dimyristoyl-3-TrimethylAmmoniumPropane (DMTAP), dipalmitoyl(C16:0)trimethyl ammonium propane (DPTAP), distearoyltrimethylammonium propane (DSTAP), N-1-(2,3-dioleyloxy)propyl]-N,N,N-trimethylammonium chloride (DOTMA), N,N-dioleoyl-N,N-dimethylammonium chloride (DODAC), 1,2-dioleoyl-sn-glycero-3-ethylphosphocholine (DOEPC), 1,2-dioleoyl-3-dimethylammonium-propane (DODAP) and 1,2-dilinoleyloxy-3-dimethylaminopropane (DLinDMA). The cationic lipid can interact with the negatively charged molecule thereby anchoring the molecule to the emulsion particles. The cationic emulsions described herein are particularly suitable for delivering nucleic acid molecules (preferably an RNA molecule encoding an antigen) to cells and formulating nucleic acid-based vaccines. The disclosure also provides a method of preparing a composition that comprises a negatively charged molecule complexed with a particle of a cationic oil-in- water emulsion, comprising: (A) preparing a cationic oil-in- water emulsion, wherein the emulsion comprises: (1) from about 0.2% to about 20% (v/v) oil, (2) from about 0.01% to about 2.5% (v/v) surfactant, and (3) a cationic lipid that is selected from the group consisting of: i. from about 0.8 mg/ml to about 1.6 mg/ml DOTAP, ii. from about 2.46 mg/ml to about 4.92 mg/ml DC Cholesterol, iii. from about 0.73
