Seasonal dynamics of influenza viruses and age distribution of infected individuals across nine seasons covering 2009-2018 in Taiwan.

BACKGROUND/PURPOSE: A swine-origin influenza A/H1N1 virus (termed A/H1N1pdm) caused a pandemic in 2009 and has continuously circulated in the human population. To investigate its possible ecological effects on circulating influenza strains, the seasonal patterns of influenza viruses and the respective age distribution of infected patients were studies. METHODS: The data obtained from national influenza surveillance systems in Taiwan from July 2009 to June 2018 were analyzed. RESULTS: The A/H1N1pdm and A/H3N2 strains usually caused a higher ratio of severe to mild cases than influenza B. New variants of A/H1N1pdm and A/H3N2 emerged accompanied by a large epidemic peak. However, the new influenza B variants intended to circulate for several seasons before causing a large epidemic. The major group of outpatients affected by A/H1N1pdm were aged 13-23 years in the pandemic wave, and the age range of infected individuals gradually shifted to 24-49 and 0-6 years across seasons; A/H1N1pdm-infected inpatients were aged 24-49 years in 2009-2011, and the age range gradually switched to older groups aged 50-65 and >65 years. Individuals aged 0-6 or 24-49 years accounted for the majority of A/H3N2-infected outpatients across seasons, whereas most of the inpatients affected by A/H3N2 were aged >65 years. CONCLUSION: Understanding the effects of new variants and changes in dominant circulating viral strains on the age distribution of the affected human population, disease severity and epidemic levels is useful for the establishment of fine-tuned strategies for further improvement of influenza control.

A virus-like particle vaccination strategy expands its tolerance to H3N2 antigenic drift by enhancing neutralizing antibodies against hemagglutinin stalk.

Seasonal influenza viruses impact public health annually due to their continual evolution. However, the current inactivated seasonal vaccines provide poor protection against antigenically drifted viruses and require periodical reformulation through hit-and-miss predictions about which strains will circulate during the next season. To reduce the impact caused by vaccine mismatch, we investigated the drift-tolerance of virus-like particles (VLP) as an improved vaccine candidate. The cross-protective humoral immunity elicited by the H3N2-VLP vaccine constructed for the 2011-2012 season was examined against viruses isolated from 2010 to 2015 in Taiwan evolving chronologically through clades 1, 4, 5, 3B and 3C, as well as viruses that were circulating globally in 2005, 2007 and 2009. Mouse immunization results demonstrated that H3N2-VLP vaccine elicited superior immunological breadth in comparison with the cognate conventional whole-inactivated virus (WIV) vaccine. Titers of neutralizing antibodies against heterologous strains representing each epidemic period in the VLP group were significantly higher than in the WIV group, indicating the antibody repertoire induced by the H3N2-VLPs was insensitive to viral antigenic drift over a span of at least 10 years. Noticeably, H3N2-VLP elicited higher levels of anti-stalk antibodies than H3N2-WIV, which offset the ineffectiveness caused by antigenic drift. This advantageous effect was attributed to the uncleaved precursor of their HA proteins. These results suggest a mechanism through which VLP-induced humoral immunity may better tolerate the evolutionary dynamics of influenza viruses and point to the possible use of a VLP vaccine as a method by which the requirement for annual updates of seasonal influenza vaccines may be diminished.

Characterization of influenza A (H7N9) viruses isolated from human cases imported into Taiwan.

A novel avian influenza A (H7N9) virus causes severe human infections and was first identified in March 2013 in China. The H7N9 virus has exhibited two epidemiological peaks of infection, occurring in week 15 of 2013 and week 5 of 2014. Taiwan, which is geographically adjacent to China, faces a large risk of being affected by this virus. Through extensive surveillance, launched in April 2013, four laboratory-confirmed H7N9 cases imported from China have been identified in Taiwan. The H7N9 virus isolated from imported case 1 in May 2013 (during the first wave) was found to be closest genetically to a virus from wild birds and differed from the prototype virus, A/Anhui/1/2013, in the MP gene. The other three imported cases were detected in December 2013 and April 2014 (during the second wave). The viruses isolated from cases 2 and 4 were similar in the compositions of their 6 internal genes and distinct from A/Anhui/1/2013 in the PB2 and MP genes, whereas the virus isolated from case 3 exhibited a novel reassortment that has not been identified previously and was different from A/Anhui/1/2013 in the PB2, PA and MP genes. The four imported H7N9 viruses share similar antigenicity with A/Anhui/1/2013, and their HA and NA genes grouped together in their respective phylogenies. In contrast with the HA and NA genes, which exhibited a smaller degree of diversity, the internal genes were heterogeneous and provided potential distinctions between transmission sources in terms of both geography and hosts. It is important to strengthen surveillance of influenza and to share viral genetic data in real-time for reducing the threat of rapid and continuing evolution of H7N9 viruses.

Newly emerging mutations in the matrix genes of the human influenza A(H1N1)pdm09 and A(H3N2) viruses reduce the detection sensitivity of real-time reverse transcription-PCR.

New variants of the influenza A(H1N1)pdm09 and A(H3N2) viruses were detected in Taiwan between 2012 and 2013. Some of these variants were not detected in clinical specimens using a common real-time reverse transcription-PCR (RT-PCR) assay that targeted the conserved regions of the viral matrix (M) genes. An analysis of the M gene sequences of the new variants revealed that several newly emerging mutations were located in the regions where the primers or probes of the real-time RT-PCR assay bind; these included three mutations (G225A, T228C, and G238A) in the A(H1N1)pdm09 virus, as well as one mutation (C163T) in the A(H3N2) virus. These accumulated mismatch mutations, together with the previously identified C154T mutation of the A(H1N1)pdm09 virus and the C153T and G189T mutations of the A(H3N2) virus, result in a reduced detection sensitivity for the real-time RT-PCR assay. To overcome the loss of assay sensitivity due to mismatch mutations, we established a real-time RT-PCR assay using degenerate nucleotide bases in both the primers and probe and successfully increased the sensitivity of the assay to detect circulating variants of the human influenza A viruses. Our observations highlight the importance of the simultaneous use of different gene-targeting real-time RT-PCR assays for the clinical diagnosis of influenza.

Phylogenetic and evolutionary history of influenza B viruses, which caused a large epidemic in 2011-2012, Taiwan.

The annual recurrence of the influenza epidemic is considered to be primarily associated with immune escape due to changes to the virus. In 2011-2012, the influenza B epidemic in Taiwan was unusually large, and influenza B was predominant for a long time. To investigate the genetic dynamics of influenza B viruses during the 2011-2012 epidemic, we analyzed the sequences of 4,386 influenza B viruses collected in Taiwan from 2004 to 2012. The data provided detailed insight into the flux patterns of multiple genotypes. We found that a re-emergent TW08-I virus, which was the major genotype and had co-circulated with the two others, TW08-II and TW08-III, from 2007 to 2009 in Taiwan, successively overtook TW08-II in March and then underwent a lineage switch in July 2011. This lineage switch was followed by the large epidemic in Taiwan. The whole-genome compositions and phylogenetic relationships of the representative viruses of various genotypes were compared to determine the viral evolutionary histories. We demonstrated that the large influenza B epidemic of 2011-2012 was caused by Yamagata lineage TW08-I viruses that were derived from TW04-II viruses in 2004-2005 through genetic drifts without detectable reassortments. The TW08-I viruses isolated in both 2011-2012 and 2007-2009 were antigenically similar, indicating that an influenza B virus have persisted for 5 years in antigenic stasis before causing a large epidemic. The results suggest that in addition to the emergence of new variants with mutations or reassortments, other factors, including the interference of multi-types or lineages of influenza viruses and the accumulation of susceptible hosts, can also affect the scale and time of an influenza B epidemic.

Genetic polymorphisms in the ITPKC gene and cervical squamous cell carcinoma risk.

Cervical cancer is caused primarily by infection with oncogenic types of human papillomavirus (HPV). However, HPV infection alone is not sufficient for the progression to cervical cancer. Host immunogenetic factors may involve in the development of this disease. Inositol 1,4,5-trisphosphate 3-kinase C (ITPKC) is recently shown to act as a negative regulator of T-cell activation. We aim to study if polymorphisms in the ITPKC gene are associated with the risk of cervical cancer in Taiwanese women. ITPKC rs28493229 C/G, rs890934 G/T, rs2303723 C/T, and rs10420685 A/G polymorphisms were genotyped in a hospital-based study of 465 women with cervical squamous cell carcinoma (CSCC) and 800 age-matched healthy control women. The presence and genotypes of HPV in CSCC were determined. The frequency of G/G genotype and G allele of the ITPKC rs28493229 polymorphism was significantly higher in patients with CSCC compared with controls (OR = 1.81, 95 % CI 1.20-2.73, P = 0.005, P (c) = 0.02; OR = 1.70, 95 % CI 1.14-2.54, P = 0.008, P (c) = 0.03, respectively). No significant associations were found for other 3 polymorphisms. Haplotype analysis revealed the distribution of haplotype CGTA was significantly reduced in women with CSCC (OR = 0.59, 95 % CI 0.40-0.89, P = 0.01, P (c) = 0.04). In conclusion, we found the G/G genotype and G allele of the ITPKC rs28493229 polymorphism may contribute to the risk of CSCC in Taiwanese women. This finding provides new insights into the mechanisms of immune activation in cervical cancer.