From the Guidelines
People with Influenza B are typically infectious starting the day before symptoms begin through approximately 5 days after illness onset. According to the study published in MMWR Recommendations and Reports 1, the duration of infectiousness for Influenza B can vary, but generally, individuals can be infectious from the day before symptoms start until about 5 days after illness onset.
Key Points to Consider
- Children can be infectious for a longer period, as stated in the study 1.
- The incubation period for influenza is 1-4 days with an average of 2 days, as reported in the study 1.
- Uncomplicated influenza illness typically resolves after several days for most persons, although cough and malaise can persist for 2 or more weeks, as noted in the study 1.
Prevention and Control Measures
To prevent spreading the virus, it is essential to practice good hygiene, including:
- Frequent handwashing
- Covering coughs and sneezes
- Disinfecting commonly touched surfaces Additionally, antiviral medications may be prescribed to reduce the duration of illness and potentially decrease the infectious period, but this should be done under medical supervision.
From the Research
Duration of Infectiousness for Influenza B
- The duration of infectiousness for Influenza B is not directly stated in the provided studies.
- However, study 2 investigated the dynamics of influenza virus shedding and symptoms, and found that most individuals shed less than 10% of their total shed virus before symptom onset.
- The study 2 also found that shedding after isolation varied substantially across individuals, isolation end points, and infectiousness assumptions.
- Study 3 mentioned that clinical studies have shown that neuraminidase inhibitors can decrease the median duration of influenza-related symptoms by approximately 1 day if initiated within 48 hours of the onset of symptoms of influenza, but it does not specify the duration of infectiousness for Influenza B.
- Study 4 compared the clinical effectiveness of four neuraminidase inhibitors for children with influenza A and B, and found that the duration of fever after administration of the first dose of the NAI was shorter in patients with influenza A infection than in patients with influenza B infection, but it does not provide information on the duration of infectiousness.
Factors Affecting Infectiousness
- Study 5 found that pneumonia was associated with delayed antiviral therapy, older age, higher Charlson score, invasive mechanical ventilation, and bacterial co-infection in patients with influenza B infection.
- Study 6 found that individuals with influenza B virus infections had higher odds of in-hospital severe outcomes, including ICU admission, mechanical ventilation or ECMO use, and death, compared to those with influenza A H3N2 virus infections.
- Study 2 found that children under 5 years experienced greater peak shedding, longer durations of shedding, and elevated ILI symptom scores compared to other age groups.