RIG-I-induced innate antiviral immunity protects mice from lethal SARS-CoV-2 infection (preprint)

The SARS-CoV-2 pandemic has underscored the need for rapidly employable prophylactic and antiviral treatments against emerging viruses. Nucleic acid agonists of the innate immune system can be administered to activate an effective antiviral program for prophylaxis in exposed populations, a measure of particular relevance for SARS-CoV-2 infection due to its efficient evasion of the host antiviral response. In this study, we utilized the K18-hACE2 mouse model of COVID-19 to examine whether prophylactic activation of the antiviral receptor RIG-I protects mice from SARS-CoV-2 infection. Systemic treatment of mice with a specific RIG-I ligand one to seven days prior to infection with a lethal dose of SARS-CoV-2 improved their survival of by up to 50 %. Improved survival was associated with lower viral load in oropharyngeal swabs and in the lungs and brain of RIG-I-treated mice. Moreover, despite antiviral protection, the surviving mice that were treated with RIG-I ligand developed adaptive SARS-CoV-2-specific immunity. These results reveal that prophylactic RIG-I activation by synthetic RNA oligonucleotides is a promising strategy to convey short-term, unspecific antiviral protection against SARS-CoV-2 infection and may be a suitable broad-spectrum approach to constraining the spread of newly emerging viruses until virus-specific therapies and vaccines become available.

Infection fatality rate of SARS-CoV-2 infection in a German community with a super-spreading event (preprint)

The world faces an unprecedented SARS-CoV2 pandemic where many critical factors still remain unknown. The case fatality rates (CFR) reported in the context of the SARS-CoV-2 pandemic substantially differ between countries. For SARS-CoV-2 infection with its broad clinical spectrum from asymptomatic to severe disease courses, the infection fatality rate (IFR) is the more reliable parameter to predict the consequences of the pandemic. Here we combined virus RT-PCR testing and assessment for SARS-CoV2 antibodies to determine the total number of individuals with SARS-CoV-2 infections in a given population. Methods: A sero-epidemiological GCP- and GEP-compliant study was performed in a small German town which was exposed to a super-spreading event (carnival festivities) followed by strict social distancing measures causing a transient wave of infections. Questionnaire-based information and biomaterials were collected from a random, household-based study population within a seven-day period, six weeks after the outbreak. The number of present and past infections was determined by integrating results from anti-SARS-CoV-2 IgG analyses in blood, PCR testing for viral RNA in pharyngeal swabs and reported previous positive PCR tests. Results: Of the 919 individuals with evaluable infection status (out of 1,007; 405 households) 15.5% (95% CI: [12.3%; 19.0%]) were infected. This is 5-fold higher than the number of officially reported cases for this community (3.1%). Infection was associated with characteristic symptoms such as loss of smell and taste. 22.2% of all infected individuals were asymptomatic. With the seven SARS-CoV-2-associated reported deaths the estimated IFR was 0.36% [0.29%; 0.45%]. Age and sex were not found to be associated with the infection rate. Participation in carnival festivities increased both the infection rate (21.3% vs. 9.5%, p<0.001) and the number of symptoms in the infected (estimated relative mean increase 1.6, p=0.007). The risk of a person being infected was not found to be associated with the number of study participants in the household this person lived in. The secondary infection risk for study participants living in the same household increased from 15.5% to 43.6%, to 35.5% and to 18.3% for households with two, three or four people respectively (p<0.001). Conclusions: While the number of infections in this high prevalence community is not representative for other parts of the world, the IFR calculated on the basis of the infection rate in this community can be utilized to estimate the percentage of infected based on the number of reported fatalities in other places with similar population characteristics. Whether the specific circumstances of a super-spreading event not only have an impact on the infection rate and number of symptoms but also on the IFR requires further investigation. The unexpectedly low secondary infection risk among persons living in the same household has important implications for measures installed to contain the SARS-CoV-2 virus pandemic.