Studies on mice showed that chitosan as an adjuvant for H5 inactivated influenza vaccines administered intramuscularly enhances significantly antibody titers and protective efficiency not only against homologous influenza viruses, but also against drift variants. Chitosan adjuvanted vaccines induced high antibody titers after a single immunization and with a low dose of antigen. High antibody titers remained for at least 6 months. Chitosan adjuvanted vaccine stored at 4 degrees C preserves its adjuvant properties for at least 8 months. Chitosan stimulates proliferative and cytotoxic activity of splenic mononuclear leukocytes in mice and promotes an increase in the numbers of CD3, CD3/NK, I-AK (MHC II), and H-2Db (MHC I) cells. After intramuscular immunization, chitosan did not induce IgE antibodies and antibodies against chitosan itself. Chitosan is a promising adjuvant candidate for inactivated influenza vaccines administered parenterally.

An escalating pandemic of the novel SARS-CoV-2 virus is impacting global health, and effective antivirals are needed. Umifenovir (Arbidol) is an indole-derivative molecule, licensed in Russia and China for prophylaxis and treatment of influenza and other respiratory viral infections. It has been shown that umifenovir has broad spectrum activity against different viruses. We evaluated the sensitivity of different coronaviruses, including the novel SARS-CoV-2 virus, to umifenovir using in vitro assays. Using a plaque assay, we revealed an antiviral effect of umifenovir against seasonal HCoV-229E and HCoV-OC43 coronaviruses in Vero E6 cells, with estimated 50% effective concentrations (EC50) of 10.0 ± 0.5 µM and 9.0 ± 0.4 µM, respectively. Umifenovir at 90 µM significantly suppressed plaque formation in CMK-AH-1 cells infected with SARS-CoV. Umifenovir also inhibited the replication of SARS-CoV-2 virus, with EC50 values ranging from 15.37 ± 3.6 to 28.0 ± 1.0 µM. In addition, 21–36 µM of umifenovir significantly suppressed SARS-CoV-2 virus titers (≥2 log TCID50/mL) in the first 24 h after infection. Repurposing of antiviral drugs is very helpful in fighting COVID-19. A safe, pan-antiviral drug such as umifenovir could be extremely beneficial in combating the early stages of a viral pandemic.

The avidity index (AI) of IgG to the RBD of SARS-CoV-2 was determined for 71 patients with a mild (outpatient) course of COVID-19, including 39 primarily and 36 secondarily reinfected, and 92 patients with a severe (hospital) course of COVID-19, including 82 primarily and 10 secondarily infected. The AI was shown to correlate with the severity of repeated disease. In the group of outpatients with a mild course, the reinfected patients had significantly higher median AIs than those with primary infections (82.3% vs. 37.1%, p < 0.0001). At the same time, in patients with a severe course of COVID-19, reinfected patients still had low-avidity antibodies (median AI of 28.4% vs. 25% in the primarily infected, difference not significant, p > 0.05). This suggests that the presence of low-avidity IgG to RBD during reinfection is a negative prognostic factor, in which a patient’s risk of developing COVID-19 in a severe form is significantly increased. Thus, patients with IgG of low avidity (AI ≤ 40%) had an 89 ± 20.5% chance of a severe course of recurrent COVID-19, whereas the detection of high-avidity antibodies (AI ≥ 50%) gave a probability of 94 ± 7.9% for a mild course of recurrent disease (p < 0.05).

Based on the results presented in this study, AV5080 is a promising novel oral drug candidate for the treatment of influenza, including oseltamivir-resistant types. Further pre-clinical development of AV5080 is warranted.

Inorganic pyrophosphatase (PPase) from E. coli was used as label in enzyme immunoassay for the detection of different plant viruses. The use of PPase‐conjugated antibodies and tetrasodium pyrophosphate as a substrate in ELISA provides some advantages in detection of plant viruses in purified preparations and extracts from plant specimens: high sensitivity, negligible level of background reactions in control samples, bright blue‐greenish colour which allows to detect the reaction visually and high stability of PPase‐conjugated antibodies.