Avian influenza A(H7N9) virus has caused 5 epidemic waves in China since its emergence in 2013. We investigated the dynamic changes of antibody response to this virus over 1 year postinfection in 25 patients in Suzhou City, Jiangsu Province, China, who had laboratory-confirmed infections during the fifth epidemic wave, Oct 1, 2016–February 14, 2017. Most survivors had relatively robust antibody responses that decreased but remained detectable at 1 year. Antibody response was variable; several survivors had low or undetectable antibody titers. Hemagglutination inhibition titer was >1:40 for <40% of the survivors. Measured in vitro in infected mice, hemagglutination inhibition titer predicted serum protective ability. Our findings provide a helpful serologic guideline for identifying subclinical infections and for developing effective vaccines and therapeutics to counter H7N9 virus infections.

H7N9 continues to cause human infections and remains a pandemic concern. Understanding the economic impacts of this novel disease is important for making decisions on health resource allocation, including infectious disease prevention and control investment. However, there are limited data on such impacts. Hospitalized laboratory-confirmed H7N9 patients or their families in Jiangsu Province of China were interviewed. Patients’ direct medical costs of hospitalization were derived from their hospital bills. A generalized linear model was employed to estimate the mean direct medical costs of patients with different characteristics. The mean direct cost of hospitalization for H7N9 was estimated to be ¥ 71 060 (95 % CI, 48 180–104 820), i.e., US$ 10 996 (95 % CI, 7 455–16 220), and was ¥12 060 (US$ 1 861), ¥136 120 (US$ 21 001) and ¥218 610 (US$ 33 728) for those who had mild or severe symptoms or who died, respectively. The principal components of the total fees differed among patients with different disease severity, although medication fees were always the largest contributors. Disease severity, proportion of reimbursement and family member monthly average income were identified as the key factors that contributed to a patient’s direct medical cost of hospitalization. The direct medical costs of hospitalized patients with H7N9 are significant, and far surpass the annual per capita income of Jiangsu Province, China. The influencing factors identified should be taken into account when developing related health insurance policies and making health resource allocation. Not applicable. This is a survey study with no health care intervention implemented on human participants.

Influenza A(H7N9) virus is known for its high pathogenicity in human. A family cluster of influenza A(H7N9) virus infection was identified in Suzhou, China. This study aimed to investigate the possibility of human-to-human transmission of the virus and examine the virologic features of this family cluster. The clinical and epidemiologic data of two patients in the family cluster of influenza A(H7N9) virus infection were collected. Viral RNA in samples derived from the two patients, their close contacts, and the environments with likely influenza A(H7N9) virus transmission were tested by real-time reverse transcriptase polymerase chain reaction (rRT-PCR) assay. Hemagglutination inhibition (HI) assay was used to detect virus-specific antibodies. Genetic sequencing and phylogenetic analysis were also performed. The index patient (Case 1), a 66-year old man, was virologically diagnosed with influenza A(H7N9) virus infection 12days after experiencing influenza-like symptoms, then died of multi-organ failure. His 39-year old daughter (Case 2), denying any other exposure to influenza A(H7N9) virus, became infected with influenza A(H7N9) virus following taking care of her father during his illness. Sequencing viral genomes isolated from the two patients showed nearly identical nucleotide sequence, and genetically resembled the viral genome isolated from a chicken in the wet market where the index patient once visited. All three influenza A(H7N9) viruses shared S138A, G186V, Q226L mutations in HA (H3) protein and a single basic amino acid (PEIPKGR↓G) at the cleavage site. Human-to-human transmission of influenza A(H7N9) virus most likely occurred in this household. The three-amino-acid mutations in HA protein were discovered in this study, which might have increased the binding affinity of influenza A(H7N9) virus to the receptor on trachea epithelial cells to facilitate viral transmission among humans.

Background: Data on influenza incidence during pregnancy in China are limited.Methods: From October 2015 to September 2018, we conducted active surveillance for acute respiratory illness (ARI) among women during pregnancy. Nurses conducted twice weekly phone and text message follow‐up upon enrollment until delivery to identify new episodes of ARI. Nasal and throat swabs were collected ≤10 days from illness onset to detect influenza.Results: In total, we enrolled 18 724 pregnant women median aged 28 years old, 37% in first trimester, 48% in second trimester, and 15% in third trimester, with seven self‐reported influenza vaccination during pregnancy. In the 18‐week epidemic period during October 2015 to September 2016, influenza incidence was 0.7/100 person‐months (95% CI: 0.5–0.9). In the cumulative 29‐week‐long epidemic during October 2016 to September 2017, influenza incidence was 1.0/100 person‐months (95% CI: 0.8–1.2). In the 11‐week epidemic period during October 2017 to September 2018, influenza incidence was 2.1/100 person‐months (95% CI: 1.9–2.4). Influenza incidence was similar by trimester. More than half of the total influenza illnesses had no elevated temperature and cough. Most influenza‐associated ARIs were mild, and <5.1% required hospitalization.Conclusions: Influenza illness in all trimesters of pregnancy was common. These data may help inform decisions regarding the use of influenza vaccine to prevent influenza during pregnancy.

Background: Recent seasonal epidemics of influenza have been caused by human influenza A viruses of the H1N1 and H3N2 subtypes and influenza B viruses. Annual vaccination is recommended to prevent infection; however, how annual influenza vaccination influences vaccine effectiveness is largely unknown.Methods: To investigate the impact of repeated vaccination on immune and protective effect, we performed a prospective seroepidemiologic study. Participants with or without prior vaccination (2018–2019) were enrolled during the 2019–2020 influenza season. Inactivated quadrivalent influenza vaccine (IIV4) was administered through the intramuscular route, and venous blood samples were collected regularly to test hemagglutination inhibition (HAI) titers.Results: The geometric mean titers and proportion with titers ≥40 against the influenza vaccine components peaked at 30 days post‐vaccination. At Day 30, the geometric mean titer and proportion with titers ≥40 in participants who had been previously vaccinated were higher for H3N2 but similar for both B lineages (Victoria and Yamagata) as compared with participants vaccinated for the first time. As for H1N1, the geometric mean titer was lower in repeated vaccinated participants, but the proportion with titers ≥40 was consistent in both groups.Conclusions: Repeated vaccination provides similar or enhanced protection as compared with single vaccination in first‐time vaccinees.

This report describes influenza hospitalization rates among pregnant and postpartum women in China with influenza.