Influenza and the Flu Vaccine

What is Influenza?

Influenza-like illnesses can be presented with respiratory symptoms such as cough, sore throat or runny nose. There are also often generalised symptoms like fevers or chills, body aches, fatigue and headaches.

Possible Complications of Influenza

While most people recover from the flu in a few days to 2 weeks, some may develop complications. Sinus and ear infections can occur. More serious and potentially life-threatening complications include infection in the lungs (pneumonia), inflammation of the heart (myocarditis), brain (encephalitis) or muscle (myositis, rhabdomyolysis) tissues, and even multi-organ failure.

Those who are at higher risk of complications include the elderly, children, pregnant women and those with chronic medical conditions (like asthma, diabetes or heart disease).

Diagnosis and Treatment

It is difficult to differentiate influenza from other viral illnesses just by symptoms. Rapid influenza diagnostic tests or molecular assays in the lab (done with nasal swabs or throat swabs) can help with the diagnosis. In suitable cases, antiviral medication can be used to treat the condition.

What is Influenza A?

Influenza A is one of the two main types of influenza viruses that cause seasonal flu epidemics. This type of virus is highly adaptable and can infect humans, birds, and other animals. Notable subtypes include H1N1 and H3N2. Symptoms of influenza A can range from mild to severe and include respiratory issues such as coughing and sore throat, as well as general symptoms like fever, body aches, and fatigue. Due to its ability to mutate rapidly, influenza A can lead to significant seasonal outbreaks and pandemics.

What is Influenza B?

Influenza B is another type of influenza virus responsible for seasonal flu infections. Unlike influenza A, influenza B primarily affects humans and is not divided into subtypes. Symptoms of influenza B are similar to those of influenza A, including respiratory symptoms and systemic effects such as fever, chills, and muscle aches. Although influenza B generally causes less severe epidemics compared to influenza A, it can still lead to serious illness, especially in high-risk groups such as children, the elderly, and those with underlying health conditions.

Influenza A vs B: The Differences

While both influenza A and B viruses cause seasonal flu and present with similar symptoms, there are key differences between them. Influenza A is known for its ability to infect a broader range of hosts, including birds and other animals, and is divided into subtypes, making it more prone to pandemics due to its high mutation rate. On the other hand, Influenza B primarily infects humans and is categorised into two lineages rather than subtypes. Although both types can lead to severe illness and complications, influenza A is often associated with more widespread outbreaks and higher variability in virus strains yearly. Understanding these differences is crucial for effective prevention and treatment strategies.

Prevention and the Influenza Vaccine

Frequent hand washing and wearing masks are helpful in preventing the spread of respiratory viruses. However, the best way to prevent the flu is by getting vaccinated annually. The flu vaccine helps protect against the four influenza viruses that research indicates are most common during the upcoming season.

OT&P offers the quadrivalent flu vaccine injection and the live attenuated intranasal flu vaccine (Flumist) for suitable cases.

The flu vaccine can help prevent you from getting sick with the flu. If you do get sick, getting the vaccine reduces the severity of illness and lowers the risk of flu-associated hospitalisation. A 2021 study showed that among vaccinated patients who were admitted to the hospital with influenza, had a 26% lower risk of intensive care admissions and 31% low risk of death from flu compared to those who were unvaccinated.

The flu shot can be beneficial as a preventative tool for people with chronic health conditions. Even if you are healthy, getting the vaccine is an important way of protecting yourself and your loved ones who may be more vulnerable. During pregnancy, it helps protect pregnant women and after pregnancy it helps protect their infants from flu in their first few months of life.

According to the Scientific Committee on Vaccine Preventable, influenza activity in Hong Kong has remained low in the past 3 years due to COVID-19 and mask wearing. Therefore, immunity against influenza in Hong Kong may be relatively weaker than the past. Local influenza activity has started to increase since March 2023. As we enter the peak season of seasonal influenza, the risk of transmission will get higher and appropriate prevention is important. The Centers for Disease Control and Prevention (CDC) recommends that in the absence of contraindications, all persons aged 6 months or above should receive the influenza vaccine annually.

If you have any questions or concerns regarding the flu vaccine, consult your healthcare provider for personalised advice and support.

Reference

1. Centers for Disease Control and Prevention. (2023, June 30). Influenza (flu). Centers for Disease Control and Prevention. Retrieved August 18, 2023, from https://www.cdc.gov/flu/index.htm.
2. Centers for Disease Control and Prevention. (2022, September 13). What are the benefits of flu vaccination?. Centers for Disease Control and Prevention. Retrieved August 18, 2023, from https://www.cdc.gov/flu/prevent/vaccine-benefits.htm.
3. Recommendations on Seasonal Influenza Vaccination for the 2023-2024 Season in Hong Kong. Scientific committee on Vaccine Preventable Diseases. (n.d.). Retrieved August 18, 2023, from https://www.chp.gov.hk/files/pdf/recommendations_on_seasonal_influenza_vaccination_for_the_2023_24_season_in_hong_kong_19apr.pdf.