ST-246 is a low-molecular-weight compound (molecular weight‫؍‬Recent concerns over the use of variola (smallpox) virus as a biological weapon have prompted renewed interest in development of small molecule therapeutics that target variola virus replication. Currently, there is no U.S. Food and Drug Administration-approved drug for the prevention or treatment of smallpox infection. While a number of compounds have been shown to inhibit orthopoxvirus replication in vitro, these compounds often lack potency and/or are associated with significant adverse effects, due to their relative nonspecific mechanisms of virus inhibition (3).The cornerstone of the current national public health response plan to a smallpox bioterrorist attack calls for rapid mass immunization with vaccinia virus. However, concerns about vaccine-related adverse events have compromised implementation of a smallpox immunization program. Individuals with immunodeficiency disorders or certain common skin conditions are unusually susceptible to vaccine-related complications (6, 32). Moreover, the lag period for antibody formation from a vaccine leaves a window of vulnerability. Antiviral therapies can fill this void and provide an excellent complement to vaccination in that they reduce virus titers quickly, regardless of immune status, and lower transmission rates by diminishing the virus reservoir. A small-molecule antiviral drug designed to treat variola virus infection will be a critical component to a smallpox defense strategy.Currently, only cidofovir [CDV; (S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine; Vistide], a drug approved for treatment of cytomegalovirus (CMV) retinitis in AIDS pa-* Corresponding author. Mailing address:

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We designed, optimized, and extensively tested several sensitive and specific real-time PCR assays for rapid detection of both smallpox and pan-orthopox virus DNAs. The assays are based on TaqMan 3-minor groove binder chemistry and were performed on both the rapid-cycling Roche LightCycler and the Cepheid Smart Cycler platforms. The hemagglutinin (HA) J7R, B9R, and B10R genes were used as targets for the variola virus-specific assays, and the HA and DNA polymerase-E9L genes were used as targets for the pan-orthopox

Successfully combating the COVID-19 pandemic depends on mass vaccination with suitable vaccines to achieve herd immunity. Here, we describe COVI-VAC, the only live attenuated severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine currently in clinical development. COVI-VAC was developed by recoding a segment of the viral spike protein with synonymous suboptimal codon pairs (codon-pair deoptimization), thereby introducing 283 silent (point) mutations. In addition, the furin cleavage site within the spike protein was deleted from the viral genome for added safety of the vaccine strain. Except for the furin cleavage site deletion, the COVI-VAC and parental SARS-CoV-2 amino acid sequences are identical, ensuring that all viral proteins can engage with the host immune system of vaccine recipients. COVI-VAC was temperature sensitive in vitro yet grew robustly (>107 plaque forming units/mL) at the permissive temperature. Tissue viral loads were consistently lower, lung pathology milder, and weight loss reduced in Syrian golden hamsters (Mesocricetus auratus) vaccinated intranasally with COVI-VAC compared to those inoculated with wild-type (WT) virus. COVI-VAC inoculation generated spike IgG antibody levels and plaque reduction neutralization titers similar to those in hamsters inoculated with WT virus. Upon challenge with WT virus, COVI-VAC vaccination reduced lung challenge viral titers, resulted in undetectable virus in the brain, and protected hamsters from almost all SARS-CoV-2–associated weight loss. Highly attenuated COVI-VAC is protective at a single intranasal dose in a relevant in vivo model. This, coupled with its large-scale manufacturing potential, supports its potential use in mass vaccination programs.