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Rising breakthrough infections of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in previously immunized individuals have raised concerns for the need for a booster vaccine dose to combat waning antibody levels and new variants. Here we report the results of the open-label, non-randomized part B of a phase 2 trial in which we evaluated the safety and immunogenicity of a booster injection of 50 µg of the coronavirus disease 2019 (COVID-19) vaccine mRNA-1273 in 344 adult participants immunized 6–8 months earlier with a primary series of two doses of 50 µg or 100 µg of mRNA-1273 (NCT04405076). Neutralizing antibody (nAb) titers against wild-type SARS-CoV-2 at 1 month after the booster were 1.7-fold (95% confidence interval (CI): 1.5, 1.9) higher than those at 28 days after the second injection of the primary series, which met the pre-specified non-inferiority criterion (primary immunogenicity objective) and might indicate a memory B cell response. The nAb titers against the Delta variant (B.1.617.2) (exploratory objective) at 1 month after the booster were 2.1-fold (95% CI: 1.8, 2.4) higher than those at 28 days after the second injection of the primary series. The seroresponse rate (95% CI (four-fold rise from baseline)) was 100% (98.7, 100.0) at 28 days after the booster compared to 98.3% (96.0, 99.4) after the primary series. The higher antibody titers at 28 days after the booster dose compared to 28 days after the second dose in the phase 3 COVE study were also observed in two assays for anti-spike IgG antibody measured by ELISA and by Meso Scale Discovery (MSD) Multiplex. The frequency of solicited local and systemic adverse reactions after the booster dose was similar to that after the second dose in the primary two-dose series of mRNA-1273 (50 µg or 100 µg); no new signals were observed in the unsolicited adverse events; and no serious adverse events were reported in the 1-month follow-up period. These results show that a booster injection of mRNA-1273 more than 6 months after completing the primary two-dose series is safe and elicited nAb titers that were statistically significantly higher than the peak titers detected after the primary vaccination series, suggesting that a booster dose of mRNA-1273 might result in increased vaccine effectiveness against infection and disease caused by SARS-CoV-2.

Updated immunization strategies are needed to address multiple severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants. Here we report interim results from an ongoing, open-label phase 2/3 trial evaluating the safety and immunogenicity of the bivalent Coronavirus Disease 2019 (COVID-19) vaccine candidate mRNA-1273.211, which contains equal mRNA amounts encoding the ancestral SARS-CoV-2 and Beta variant spike proteins, as 50-µg (n= 300) and 100-µg (n= 595) first booster doses administered approximately 8.7–9.7 months after the mRNA-1273 primary vaccine series (NCT04927065). The primary objectives were to evaluate the safety and reactogenicity of mRNA-1273.211 and to demonstrate non-inferior antibody responses compared to the mRNA-1273 100-µg primary series. Additionally, a pre-specified immunogenicity objective was to demonstrate superior antibody responses compared to the previously authorized mRNA-1273 50-µg booster. The mRNA-1273.211 booster doses (50-µg or 100-µg) 28 days after immunization elicited higher neutralizing antibody responses against the ancestral SARS-CoV-2 and Beta variant than those elicited 28 days after the second mRNA‑1273 dose of the primary series (NCT04470427). Antibody responses 28 days and 180 days after the 50-µg mRNA-1273.211 booster dose were also higher than those after a 50-µg mRNA-1273 booster dose (NCT04405076) against the ancestral SARS-CoV-2 and Beta, Omicron BA.1 and Delta variants, and all pre-specified immunogenicity objectives were met. The safety and reactogenicity profile of the bivalent mRNA-1273.211 booster (50-µg) was similar to the booster dose of mRNA-1273 (50-µg). Immunization with the primary series does not set a ceiling to the neutralizing antibody response, and a booster dose of the bivalent vaccine elicits a robust response with titers that are likely to be protective against COVID-19. These results indicate that bivalent booster vaccines can induce potent, durable and broad antibody responses against multiple variants, providing a new tool in response to emerging variants.

New hepatitis C virus (HCV) therapies with pan-genotypic efficacy are needed. The goals of part A of C-CREST-1 and C-CREST-2 were to compare the efficacies of two doses (300 mg or 450 mg once daily) of uprifosbuvir (MK-3682; NS5B inhibitor) in an 8-week regimen combined with grazoprevir (NS3/4A inhibitor; 100 mg once daily) and an NS5A inhibitor, either elbasvir (50 mg once daily) or ruzasvir (MK-8408; 60 mg once daily), and to evaluate the safety and tolerability of these combination regimens in individuals infected with genotypes 1, 2, or 3.

There is a need for hepatitis C virus (HCV) therapies with excellent efficacy across genotypes and in diverse populations. Part A of the C-CREST-1 and C-CREST-2 trials led to the selection of a three-drug regimen of grazoprevir (MK-5172; an HCV NS3/4A protease inhibitor; 100 mg/day) plus ruzasvir (MK-8408; an NS5A inhibitor; 60 mg/day) plus uprifosbuvir (MK-3682; an HCV NS5B polymerase inhibitor; 450 mg/day). Part B of the studies tested this combination as a single formulation in different treatment durations in a broader population.

The three-dimensional structures of two human rhinovirus serotypes (HRV14 and HRV1A) are compared when complexed with various antiviral agents. Although these agents all bind into the same hydrophobic pocket, the exact viral-drug interactions differ. In the absence of drugs, the pocket is occupied by a fatty acid in HRV1A, but is empty in HRV14 except for two water molecules. The conformation of each drug is dependent upon the shape of the hydrophobic pocket. In HRV14the major residues determining the shape of the binding site are Y1128, P1174and M1224, corresponding to I1125, M1169 and I1220 in HRV1A. When there is no cofactor or a drug in the pocket, the entrance to the pocket is open. However, the entrance is closed when the pocket is occupied by a cofactor or a drug. There are relatively small conformational changes when the agents displace the natural cofactor in HRV1A. In contrast, there are much larger conformational changes on binding a drug in HRV14. These differences cause an inhibition of viral attachment in HRV14 but not in HRV1A. Binding of the drugs results in three additional interprotomer hydrogen bonds in HRV14 and one in HRV1A. These hydrogen bonds and a potential loss of flexibility upon efficient packing of the pocket may contribute to the inhibition of uncoating in both serotypes.

Cryatallographic studies of human rhinovirus 14 (HBV14) crystals soaked with fragments of antiviral WIN compounds, at high concentrations (82-200 µg/ml), show the compounds bind into the hydrophobic β-barrel (WIN pocket) of VP1. Two of these short compounds (5-[3,5-dimethyl-4-hydroxyphonyl]-2-methyltetrazole and phenol oxazoline) cause conformational changes in the virus similar to the active, longer WIN compounds. In addition, thermostabilization studies suggest these short WIN compounds provide some stability to the HBV14 capsid. We conclude that the short compounds appear to mimic the cellular cofactors observed in the hydrophobic pocket of VP1 for some picornaviruses. Both cofactors and short WIN compounds bind into the pocket, cause conformational changes in VP1, and provide a small degree of virion stabilization but are unlikely to inhibit attachment. Three specific binding sites for dimethyl sulfoxide (DMSO), used as solvent, were also identified. One of the DMSO molecules binds into the drug binding pocket near the pocket opening, while the other two bind in the canyon near the VP1 protomer-protomer interface. Copyright 1994, 1999 Academic Press