Defective Interfering Particles of Influenza Virus and Their Characteristics, Impacts, and Use in Vaccines and Antiviral Strategies: A Systematic Review.

Defective interfering particles (DIPs) are particles containing defective viral genomes (DVGs) generated during viral replication. DIPs have been found in various RNA viruses, especially in influenza viruses. Evidence indicates that DIPs interfere with the replication and encapsulation of wild-type viruses, namely standard viruses (STVs) that contain full-length viral genomes. DIPs may also activate the innate immune response by stimulating interferon synthesis. In this review, the underlying generation mechanisms and characteristics of influenza virus DIPs are summarized. We also discuss the potential impact of DIPs on the immunogenicity of live attenuated influenza vaccines (LAIVs) and development of influenza vaccines based on NS1 gene-defective DIPs. Finally, we review the antiviral strategies based on influenza virus DIPs that have been used against both influenza virus and SARS-CoV-2. This review provides systematic insights into the theory and application of influenza virus DIPs.

Development of a T Cell-Based COVID-19 Vaccine Using a Live Attenuated Influenza Vaccine Viral Vector.

The COVID-19 pandemic emerged in 2020 and has caused an unprecedented burden to all countries in the world. SARS-CoV-2 continues to circulate and antigenically evolve, enabling multiple reinfections. To address the issue of the virus antigenic variability, T cell-based vaccines are being developed, which are directed to more conserved viral epitopes. We used live attenuated influenza vaccine (LAIV) virus vector to generate recombinant influenza viruses expressing various T-cell epitopes of SARS-CoV-2 from either neuraminidase (NA) or non-structural (NS1) genes, via the P2A self-cleavage site. Intranasal immunization of human leukocyte antigen-A*0201 (HLA-A2.1) transgenic mice with these recombinant viruses did not result in significant SARS-CoV-2-specific T-cell responses, due to the immunodominance of NP366 influenza T-cell epitope. However, side-by-side stimulation of peripheral blood mononuclear cells (PBMCs) of COVID-19 convalescents with recombinant viruses and LAIV vector demonstrated activation of memory T cells in samples stimulated with LAIV/SARS-CoV-2, but not LAIV alone. Hamsters immunized with a selected LAIV/SARS-CoV-2 prototype were protected against challenge with influenza virus and a high dose of SARS-CoV-2 of Wuhan and Delta lineages, which was confirmed by reduced weight loss, milder clinical symptoms and less pronounced histopathological signs of SARS-CoV-2 infection in the lungs, compared to LAIV- and mock-immunized animals. Overall, LAIV is a promising platform for the development of a bivalent vaccine against influenza and SARS-CoV-2.

Sequential Delivery of Live Attenuated Influenza Vaccine and Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) in the Ferret Model Can Reduce SARS-CoV-2 Shedding and Does Not Result in Enhanced Lung Pathology.

Cocirculation of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and influenza viruses could pose unpredictable risks to health systems globally, with recent studies suggesting more severe disease outcomes in coinfected patients. The initial lack of a readily available coronavirus disease 2019 (COVID-19) vaccine has reinforced the importance of influenza vaccine programs during the COVID-19 pandemic. Live attenuated influenza vaccine (LAIV) is an important tool in protecting against influenza, particularly in children. However, it is unknown whether LAIV administration influences the outcomes of acute SARS-CoV-2 infection or disease. To investigate this, quadrivalent LAIV was administered to ferrets 3 days before or after SARS-CoV-2 infection. LAIV administration did not exacerbate the SARS-CoV-2 disease course or lung pathology with either regimen. In addition, LAIV administered before SARS-CoV-2 infection significantly reduced SARS-CoV-2 replication and shedding in the upper respiratory tract. This study demonstrated that LAIV administration in close proximity to SARS-CoV-2 infection does not exacerbate mild disease and can reduce SARS-CoV-2 shedding.

Nasal spray live attenuated influenza vaccine: the first experience in Italy in children and adolescents during the 2020-21 season.

BACKGROUND: In Italy only recently, for the 2020-21 season, has the flu vaccination been extended to all children. A quadrivalent live attenuated influenza vaccine (qLAIV) was administered to children aged 2-17 years for the first time. We registered the number and severity of adverse reactions to (Fluenz Tetra™) and the factors influencing them, evaluated uniformity of access to care and assessed the degree of satisfaction with the vaccination of both parents and health care providers, in order to improve the 2021-22 vaccination program. METHODS: On vaccination day, a questionnaire was given out to collect information about the children and their parents. Between 1 and 3 months later, the parents were contacted to record any adverse reactions following (Fluenz Tetra™) and rate the degree of satisfaction. RESULTS: We received data of 3226 children from 2152 families. Adverse events were reported in 24.8% of children: 80.6% mild, 18.1% moderate and 1.3% significant. The most common were rhinitis (52.5%) and fever (24.4%). Statistical analysis performed with a multiple regression model, showed that children aged 2-5 years have an increased risk of adverse events compared to both 6-10 years old (aRR 1.7, 95% CI 1.5-1.9, p < 0. 001) and 11-17 years old (aRR 1.5, 95% CI 1-2.2, p = 0.051). Most families chose to vaccinate their children to protect them and because they were concerned about Covid19. The main channel through which parents became aware of a new flu vaccination was word-of-mouth (39.8%), which occurred mostly among parents of the same school group, followed by information from the child's doctor (30.6%), the Internet (26.9%), personal research (15%), newspapers (4%), telecommunications (7.5%) and other (2.6%). Most parents (83.3%) were very satisfied and intend to vaccinate their children with qLAIV again (83.8%). The majority of operators (93%) considered the experience as excellent and are willing to repeat it (94.6%). CONCLUSION: (Fluenz Tetra™) proved to be easy to administer and the degree of satisfaction was high among both health workers and parents. Considering its substantial safety profile especially in school-age children and adolescents, all these aspects make the nasal qLAIV optimal for widespread immunization. Schools offer the best setting to reach more families and physicians should be actively involved.