Dr Ling Moi Lin, Director of Infection Prevention & Epidemiology from Singapore General Hospital (SGH), a member of the SingHealth group, shares why it is important to stay flu-safe amidst the COVID-19 pandemic.

How many flu seasons do we have in a year?

You always seem to hear that it's flu season time (again) in Singapore. Why? 

"The flu season occurs between fall and winter seasons around the world. Divided into the Northern and Southern hemispheres, the flu virus is different for both sides of the equator. For us in sunny Singapore, we are (un)lucky enough to be right in the middle of both Northern and Southern hemisphere changes, and thus we are affected by both the prevailing flu strains!" explains Dr Ling.

"The months that we (in Singapore) are affected typically range from May-July and December-February," she adds.

Types of flu virus

The flu (influenza) virus can be categorised into 3 types (A, B and C). Types A and B are responsible for seasonal epidemics (and flu vaccines are designed to combat these stronger types of the flu virus), while Type C only causes mild respiratory illness. 

Here are the differences:

​Type A
(Seasonal, Avian, Swine Influenza)

​Type B (Seasonal Influenza)
​Can cause significant disease​Generally causes milder disease but may also cause severe disease
​Infectious to humans and other species (e.g. birds; H5N1)​Limited to humans
​Can cause epidemics and pandemics (worldwide epidemics)​Generally causes milder epidemics

The Type C virus only causes mild respiratory illness so it is not a cause for concern.

"As the influenza virus is a living organism, it constantly adapts to the environment and conditions in order to stay alive. That is why it is important to refresh your flu vaccination every year," Dr Ling explains.

How is the flu spread?

The flu (influenza) is spread mainly in two ways:

  1. Person to person: When a person with influenza spreads droplets through coughing and sneezing (droplets can propel up to 1m through the air)
  2. Through touch: A person can become infected by touching an object or a surface that has the influenza virus on it and then touching their mouth, eyes or nose

"Thanks to current safe distancing, mask wearing and hand hygiene measures in Singapore to curb the spread of COVID-19, we can expect a drop in flu transmission as well (because both are transmitted in largely the same way)" Dr Ling shares.

"However, it is important to still get flu vaccinated as the virus can spread even when no symptoms are present* (asymptomatic)."

How to tell if you have the flu

Symptoms of the flu (influenza) include:

  • Sudden onset

  • Typically starts with a headache, chills and cough, followed rapidly by fever, loss of appetite, muscle aches and fatigue, runny nose, sneezing, watery eyes and throat irritation

  • Nausea, vomiting and diarrhoea may also occur (especially in children)

  • Fever may not be prominent in children under 5 years of age and adults 65 years of age and older

Complications that can arise from the flu

​Pneumonia
(secondary
and bacterial)
- Respiratory failure

​Myocarditis​Pericarditis​Death from overwhelming sepsis can progress rapidly
​Myositis​Reye's syndrome​Otitis media​Exacerbates underlying medical conditions e.g. pulmonary, cardiac or metabolic disease ​
​Encephalopathy​Bronchitis​Acute Myocardial Infarction (AMI)

The flu vs COVID-19

Similarities

Both the flu (influenza) and COVID 19: 

  • Are transmitted by respiratory droplets from an infected person

  • Can cause fever, cough, fatigue 

Differences

Flu (Influenza)​COVID-19
​Symptoms​Begin 1-4 days after exposureBegin 1-14 days after exposure​
​Causes
Influenza virus
(there are many strains)​
​SARS-CoV-2 virus
​Complications​Less likely to occur because of immunity built up over timeSevere respiratory complications may come on extremely quickly​
​Prevention

​Flu vaccine

​Self-isolation
(No vaccine available yet)

* Based on the 2015 Southern Hemisphere Influenza and Vaccine Effectiveness Research and Surveillance (SHIVERS) influenza research sero-survey in New Zealand that showed 80 per cent of those infected with influenza were asymptomatic carriers.

Ref: L20