Influenza is associated with an increased risk for serious illness, hospitalization and death in pregnant women and young infants. The investigators estimated the effectiveness of a quadrivalent inactivated influenza vaccine (QIV) in pregnant women and their infants in 2019-2020 influenza season. Women were activelly followed during the influenza season on a weekly basis through telephone call in order to collect data about the onset of fever and/or respiratory symptoms by them or their young infants. Polymerase chain reaction testing in pharyngeal samples was offered to pregnant women and infants with influenza-like illness (ILI). A total of 636 pregnant women and 474 infants were studied. A Bayesian beta-binomial model was used.

Study period: Influenza 2019-2020 season

The investigators followed actively the pregnant women and their infants in order to collect prospectively data on a weekly basis through phone calls during the entire influenza season.

Definitions:

• ILI was defined as the sudden onset of symptoms and fever, malaise, myalgia or headache, and cough, sore throat or shortness of breath.
• ARI was defined as the presence of at least one respiratory symptom, regardless of fever.
• Febrile episode was defined as the presence of fever only.
• Fever was defined as a temperature of 38.0 C in at least two measurements within 24h.
• The diagnoses of pneumonia and AOM were accepted as reported by the physicians who provided care to the women or their infants.

The 2019-2020 QIV Vaxigrip-Tetra was used to vaccinate pregnant women.

Inclusion Criteria:

Pregnant women >18 years old and <45 years old, cared at Alexandra General Hospital (Athens, Greece) between October 16 and January 27, 2020

Exclusion Criteria:

• <18 years old or >45 years old
• not in stable health
• already vaccinated against influenza
• history of Guillain-Barré syndrome
• history of hypersensitivity to influenza vaccines
• immunosuppression
• history of investigational drug <30 days
• history of immunoglobulins or blood products <3 months
• fever at day of interview (enrollment day)

Pregnant women and their infants

In order to share IPD we should request permission from the Ethics Committee of the hospital.