The general population is susceptible to influenza virus transmission via droplets, aerosols, and direct or indirect contact. Typical clinical manifestations are systemic symptoms such as sudden chills, high fever, headache, general soreness, and weakness; while the respiratory symptoms are mild . In our study, the age at onset for neonates with influenza A was 3–28 days. After birth, these neonates had an obvious history of contact with febrile patients (mother or other family members), and all of them developed symptoms during the influenza incubation period—which is consistent with the typical course of influenza A. The principal source of infection for neonates with influenza A is their caregivers, although the neonates have atypical symptoms due to their low immunity. In addition to fever, nasal congestion, runny nose, sneezing and coughing in neonates with influenza A in our study, digestive symptoms such as spitting up and choking on milk, anorexia, and diarrhea are also relatively common—which is consistent with previous reports [7–8]. Neonates with influenza A may have reduced white blood cell and neutrophil counts, and slightly increased C-reactive protein; but whether antibiotic treatment is needed depends upon the comprehensive assessment of neonatal symptoms, physical signs, and laboratory tests so as to avoid antibiotic abuse.
In the present study, all cases were positive for influenza A virus antigen, and the positivity rate for nucleic acid testing for influenza A virus was 88.9%. One of the cases was negative for nucleic acid testing, but we could not exclude a false-negative due to the collection site of the specimen being unsatisfactory. However, in combination with typical fever symptoms and contact history with febrile patients, all 9 neonates met the clinical diagnostic criteria for influenza A; and 8 neonates met the defined diagnostic criteria for influenza A.
Prompt diagnosis and early antiviral treatment are the most important strategies for treating influenza. Antiviral treatment is best for neonates within 48 hours of symptoms, but for neonates with severe illness or a high risk of complications, antiviral treatment should still be considered 48 hours after symptoms appear . One neonate in the present study was started on antiviral therapy 5 days after the onset of the disease, and the prognosis was still favorable despite the long treatment time. At present, oral oseltamivir is still the first choice for treating childhood influenza; but paramivir can also be a treatment of choice for neonates at certain dosages (see Table 2 for specific dosages). Therefore, early detection, early diagnosis, and early treatment are the primary means to be used to reduce the mortality and serious complications of neonatal influenza .
Influenza virus infection during pregnancy can increase the risks of spontaneous abortion, premature delivery, stillbirth, and low birth weight [11–12]. Pregnant women, especially after infection in the third trimester, can also easily develop critical illnesses that can result in death . Influenza vaccination of pregnant women not only effectively prevents maternal influenza during the influenza season, but also produces protective antibodies that can pass through the placental barrier; and thus effectively prevents infection in infants under 6 months of age who are not suitable for influenza vaccination [14–15]. In developed countries such as the United States, the influenza vaccination rate for pregnant women has approached or exceeded 50% [16–17], while the influenza vaccination rate of pregnant women in China has been very low . The latest guidelines suggest  that pregnant women be vaccinated at any stage of pregnancy, and that the prevention of contracting influenza by infants under 6 months of age occur through the vaccination of their mothers during pregnancy, and also of their family members and caregivers.
In summary, the symptoms of neonatal influenza A are often atypical. In addition to fever, nasal congestion, runny nose, sneezing, coughing, and other respiratory symptoms; digestive symptoms such as spitting up milk, choking on milk, reduced milk intake, and diarrhea are also relatively common. Early diagnosis and antiviral treatment can effectively improve clinical symptoms and reduce complications, and paramivir is relatively safe for neonatal use.