Carbohydrate fatty acid monosulphate ester is a potent adjuvant for low-dose seasonal influenza vaccines.

There is still a need for a better and affordable seasonal influenza vaccine and the use of an adjuvant could solve both issues. Therefore, immunogenicity of a combination of low dose of 1/5 (3 µg of HA) a licensed seasonal flu vaccine with the novel carbohydrate fatty acid monosulfate ester (CMS)-based adjuvant was investigated in ferrets and safety in rabbits. Without CMS, hemagglutination inhibition (HI) antibody titers ranged from ≤5 to 26 three weeks post immunization 1 (PV-1) and from 7 to 134 post-immunization 2 (PV-2) in ferrets. Virus neutralizing (VN) antibody titers ranged from 20 to 37 PV-1 and from 21 to 148 PV-2. CMS caused 10 to 111- fold increase in HI titers and 3 to 58- fold increase in VN titers PV-1 and PV-2, depending on influenza strain and dose of adjuvant. Eight mg of CMS generated significantly higher antibody titers than 1 or 4 mg, while 1 and 4 mg induced similar responses. Three µg of HA plus 4 mg of CMS was considered the highest human dose and safety of two-fold this dose was determined in acute and repeated-dose toxicity studies in rabbits conducted according to OECD GLP guidelines. The test item did not elicit any clinical signs, local reactions, effect on body weight, effect on urine parameters, effect on blood biochemistry, or gross pathological changes. In blood, increased numbers of neutrophils, lymphocytes and/or monocytes were noted and in iliac lymph nodes, increased cellularity of macrophages of minimal to mild degree were observed. In both ferrets and rabbits, body temperature increased with increasing dose of CMS to a maximum of 1 ˚C during the first day post-immunization, which returned to normal values during the second day. In the local tolerance study, histopathology of the site of injection at 7 days PV-1 revealed minimal, mild or moderate inflammation in 5, 8 and 5 animals, respectively. In the repeated-dose study and 21 days PV-3, minimal, mild or moderate inflammation was observed in 15, 18 and 3 animals, respectively. We concluded that the data show CMS is a potent and safe adjuvant ready for further clinical development of a seasonal influenza vaccine and combines high immunogenicity with possible antigen-sparing capacity.