Prophylaxis and treatment of influenza: options, antiviral susceptibility, and existing recommendations

Molecular Determinants of Drug Resistance and Mutation Patterns in Influenza Viruses Circulating in Poland Across Multiple Epidemic Seasons: Implications for Vaccination Strategies

BACKGROUND According to the WHO, up to 650 000 people die each year from seasonal flu-related respiratory illnesses. The most effective method of fighting the virus is seasonal vaccination. However, if an infection does occur, antiviral medications should be used as soon as possible. No studies of drug resistance in influenza viruses circulating in Poland have been systematically conducted. Therefore, the aim of the present study was to investigate the drug resistance and genetic diversity of influenza virus strains circulating in Poland by determining the presence of mutations in the neuraminidase gene. MATERIAL AND METHODS A total of 258 clinical specimens were collected during the 2016-2017, 2017-2018, and 2018-2019 epidemic seasons. The samples containing influenza A and B were analyzed by RT-PCR and Sanger sequencing. RESULTS Differences were found between the influenza virus strains detected in different epidemic seasons, demonstrating the occurrence of mutations. Influenza A virus was found to be more genetically variable than influenza B virus (P<0.001, Kruskal-Wallis test). However, there was no significant difference in the resistance prevalence between the influenza A subtypes A/H1N1/pdm09 (4.8%) and A/H3N2/ (6.1%). In contrast, more mutations of drug-resistance genes were found in the influenza B virus (P<0.001, chi-square test). In addition, resistance mutations appeared en masse in vaccine strains circulating in unvaccinated populations. CONCLUSIONS It seems important to determine whether the influenza virus strains tested for drug resistance as part of global influenza surveillance are equally representative of viruses circulating in populations with high and low vaccination rates, for all countries. Our results suggest that countries with low levels of influenza immunization may constitute reservoirs of drug-resistant influenza viruses.

Correlation of bioactive marker compounds of an orally applied Morus alba root bark extract with toxicity and efficacy in BALB/c mice

Introduction: In traditional Chinese medicine, the root bark of Morus alba L. is used to treat respiratory infections. Recently, anti-inflammatory and multiple anti-infective activities (against influenza viruses, corona virus 2, S. aureus, and S. pneumoniae) were shown in vitro for a standardized root bark extract from M. alba (MA60). Sanggenons C and D were identified as major active constituents of MA60. The aim of the present preclinical study was to evaluate, whether these findings are transferable to an in vivo setting. Methods: MA60 was orally administered to female BALB/c mice to determine 1) the maximum tolerated dose (MTD) in an acute toxicity study and 2) its anti-influenza virus and anti-inflammatory effects in an efficacy study. A further aim was to evaluate whether there is a correlation between the obtained results and the amount of sanggenons C and D in serum and tissues. For the quantitation of the marker compounds sanggenons C and D in serum and tissue samples an UPLC-ESI-MS method was developed and validated. Results: In our study setting, the MTD was reached at 100 mg/kg. In the efficacy study, the treatment effects were moderate. Dose-dependent quantities of sanggenon C in serum and sanggenon D in liver samples were detected. Only very low concentrations of sanggenons C and D were determined in lung samples and none of these compounds was found in spleen samples. There was no compound accumulation when MA60 was administered repeatedly. Discussion: The herein determined low serum concentration after oral application once daily encourages the use of an alternative application route like intravenous, inhalation or intranasal administration and/or multiple dosing in further trials. The established method for the quantitation of the marker sanggenon compounds in tissue samples serves as a basis to determine pharmacokinetic parameters such as their bioavailability in future studies.

Preparing for the Next Influenza Season: Monitoring the Emergence and Spread of Antiviral Resistance

Purpose

The relaxation of pandemic restrictions in 2022 has led to a reemergence of respiratory virus circulation worldwide and anticipation of substantial influenza waves for the 2022/2023 Northern Hemisphere winter. Therefore, the antiviral susceptibility profiles of human influenza viruses circulating in Germany were characterized.

Methods

Between October 2019 (week 40/2019) and March 2022 (week 12/2022), nasal swabs from untreated patients with acute respiratory symptoms were collected in the national German influenza surveillance system. A total of 598 influenza viruses were isolated and analyzed for susceptibility to oseltamivir, zanamivir and peramivir, using a neuraminidase (NA) inhibition assay. In addition, next-generation sequencing was applied to assess molecular markers of resistance to NA, cap-dependent endonuclease (PA) and M2 ion channel inhibitors (NAI, PAI, M2I) in 367 primary clinical samples. Furthermore, a genotyping assay based on RT-PCR and pyrosequencing to rapidly assess the molecular resistance marker PA-I38X in PA genes was designed and established.

Results

While NAI resistance in the strict sense, defined by a ≥ 10-fold (influenza A) or ≥5-fold (influenza B) increase of NAI IC₅₀, was not detected, a subtype A(H1N1)pdm09 isolate displayed 2.3- to 7.5-fold IC₅₀ increase for all three NAI. This isolate carried the NA-S247N substitution, which is known to enhance NAI resistance induced by NA-H275Y. All sequenced influenza A viruses carried the M2-S31N substitution, which confers resistance to M2I. Of note, one A(H3N2) virus displayed the PA-I38M substitution, which is associated with reduced susceptibility to the PAI baloxavir marboxil. Pyrosequencing analysis confirmed these findings in the original clinical specimen and in cultured virus isolate, suggesting sufficient replicative fitness of this virus mutant.

Conclusion

Over the last three influenza seasons, the vast majority of influenza viruses in this national-level sentinel were susceptible to NAIs and PAIs. These findings support the use of antivirals in the upcoming influenza season.

Pre-Exposure Prophylaxis for viral infections other than HIV

The battle against human viral infections has historically relied on two medical strategies, namely vaccines to protect from contagion and antivirals to treat infected patients. In the absence of vaccines, antivirals have occasionally been used as peri-exposure prophylaxis, given either before (pre-exposure prophylaxis) or right after (post-exposure prophylaxis). In an unprecedented way, the use of antiretrovirals as chemoprophylaxis has triumphed in the HIV field. Indeed, oral antiretrovirals given either daily or at demand to HIV-uninfected individuals engaged in high-risk behaviors protect from contagion. More recently, the advent of long-acting formulations has allowed HIV protection following intramuscular injections every three months. Can we envision a similar prophylactic strategy for other human viral infections? The advent of such 'chemical vaccines' would fill an unmet need when classical vaccines do not exist, cannot be recommended, immune responses are suboptimal, escape mutants emerge or immunity wanes. In this review, we discuss the opportunities for antiviral chemoprophylaxis for viral hepatitis B and C, retroviruses HTLV-1 and HIV-2, and respiratory viruses influenza and SARS-CoV-2, among others.