What is it?

COVID-19 is a disease caused by the coronavirus SARS-CoV-2. Coronaviruses can cause a range of illnesses, from mild respiratory infections to more serious disease affecting multiple organs and systems. SARS-CoV-2 is a highly contagious strain of coronavirus discovered in 2019. It is a strain that had not been previously detected in humans that spread rapidly, resulting in a global pandemic.  

COVID-19 disease can be asymptomatic, cause mild to moderate symptoms or can progress to severe illness in over 10% of people, requiring hospitalisation and mechanical ventilation, or even death. Even when infections are asymptomatic; individuals can still transmit disease to other people.  

Tens of millions of people have been infected with COVID-19 globally and millions have died. The virus has had vast impacts on society, not only from a public health perspective, but the economic, social and mental health effects have been and continue to be, enormous. 

What to look for?

Common symptoms of acute COVID-19 infection include: 

  • fever 
  • cough 
  • myalgia (body aches) 
  • dyspnoea (difficulty breathing) 
  • gastrointestinal symptoms such as diarrhoea, nausea or vomiting 
  • headache 
  • sore throat 
  • loss of smell or taste 
  • rhinorrhoea (runny nose).  

Some individuals can experience ongoing symptoms for weeks or months after their initial diagnosis, this is known as long COVID or post-COVID conditions. Long COVID is more common in people who have experienced severe COVID disease, those have underlying medical conditions, older people, females and unvaccinated individuals. However, long COVID can also be experienced by people who have experienced mild or asymptomatic disease. Symptoms can include: 

  • extreme fatigue 
  • post-exertional malaise  
  • shortness of breath  
  • chest pain 
  • palpitations  
  • fever  
  • arthralgia (joint pain) 
  • paresthesia (pins and needles) 
  • rash 
  • hoarse voice 
  • problems with memory and concentration (brain fog) 
  • sleep problems  
  • changes with taste or smell 
  • gastrointestinal symptoms such as diarrhoea and abdominal pain  
  • changes in menstrual cycles  
  • weight loss and poor appetite  
  • mood changes (depression, anxiety) 
  • difficulty completing activities of daily living.  

How is it transmitted?

COVID-19 is transmitted via aerosol when an infected person breathes out droplets and virus particles and these are breathed in by other people, or via droplet when particles land on their faces, noses or mouths. Surfaces can also be contaminated with these droplets or particles. COVID-19 can spread in poorly ventilated settings as aerosol particles can remain in the air, with larger droplets settling within seconds to minutes and smaller droplets remaining suspended in the air for minutes to hours.

The incubation period for the disease is 1-14 days, with most individuals displaying symptoms displaying symptoms 5-6 days after being exposed. Individuals are thought to be infectious up to 48 hours before symptoms appear and are most infectious in this prodromal period and the early stages of their illness. People with asymptomatic disease can still infect others.  


Globally, there have been over 750 million cases of COVID-19 since the emergence of the disease and over 6 million deaths. Multiple strains of SARS-CoV-2 have emerged and public health authorities continue to monitor these. Multiple variants of concern have been identified, with the Omicron strain currently being the most dominant variant, and has been shown to be more transmissible than previous variants.  


Strategies to reduce risk of transmission of COVID-19 disease include standard precautions such as hand hygiene, wearing a mask indoors when remaining socially distant is not possible and ensuring good ventilation.  


Vaccination against COVID-19 disease aims to reduce the severity of symptoms and need for hospitalisations. Recommendations are based on an individual’s level of risk of severe disease. Individuals at the highest risk are older people (the risk of severe disease increases with each decade over 50), immunocompromised individuals, Aboriginal and Torres Strait Islander peoples, pregnant women and people with severe mental illness and individuals at a higher occupational risk.  

An interval of 3 months between COVID-19 infection and COVID-19 vaccination (primary dose or booster dose) is recommended.

Children and adolescents 6 months to ≤ 17 years of age

  • Primary schedule

    COVID-19 vaccination is recommended for all children aged ≥ 5 years of age. It is also recommended for some children aged 6 months to ≤ 5 years including those with severe immunocompromise, disability or complex medical condition that places them at a higher risk of severe COVID-19 disease. Children aged 6 months-≤ 5 years who do not fit these criteria are not recommended to be vaccinated at this time.

    For more information please refer to MVEC: COVID-19 vaccination in children and adolscents

  • Booster doses

    Following a primary course, booster doses are recommended for some children aged 5 years and over.

    For more information please refer to MVEC: COVID-19 vaccination in children and adolescents

Adults ≥ 18 years of age

  • Primary schedule

    § for a full list of immunocompromising conditions requiring a 3 dose primary course of COVID-19 vaccines refer to ATAGI recommendations on the sue of a third primary dose of COVID-19 vaccine in indiviudals who are severely immunocompromised
    € Comirnaty (Pfizer), Spikevax (Moderna) or Nuvaxovid (Novavax) are the preferred vaccine options for individuals with severe immunocompromise
    £ whilst there are no safety concerns in administering Nuvaxovid (Novavax) to patients with severe immuncompromise, there is limited evidence of vaccine efficacy and patients should be informed of this.

  • Booster doses

    Following a primary course, booster doses are recommended for all individuals aged ≥ 18 years.

    For more information on booster dose frequency and intervals refer to Clinical recommendations for COVID-19 vaccines.

Side effects following vaccination

Common side effects 

Most side effects following COVID-19 vaccination are mild and can include pain at the injection site, fatigue, headache, lymphadenopathy and fever. Surveillance of adverse events occurring in Australian adolescents has shown that these symptoms typically resolve within 3 days.  

For more information on the expected side effects of the vaccines in use in Australia refer to the following: 

Rare side effects  

Myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the lining around the heart) are rare conditions that have been reported following administration of COVID-19 vaccines. They are most commonly associated with viral infections (including COVID-19 disease) but can also be triggered by other factors such as medications and autoimmune conditions. In the setting of vaccination the peak risk group for myocarditis is young adult males aged between 16-24 years old following a second dose of vaccination. Pericarditis occurring after vaccination is more common in the 20-45 year old age group for both males and females. 

A rare side effect of the Vaxzevria (AstraZeneca) vaccine is thrombosis with thrombocytopenia (TTS). Symptoms of TTS may include a severe, persistent headache that does not settle with analgesia, abdominal pain, significant respiratory problems/distress, visual changes, vomiting, seizures, focal neurological deficits/changes, confusion/encephalopathy and usually occur 4-30 days after vaccination. 


Authors: Francesca Machingaifa (MVEC Education Nurse Coordinator) and Rachael McGuire (MVEC Education Nurse Coordinator)

Date: February 9, 2023

Materials in this section are updated as new information and vaccines become available. The Melbourne Vaccine Education Centre (MVEC) staff regularly reviews materials for accuracy.

You should not consider the information in this site to be specific, professional medical advice for your personal health or for your family’s personal health. For medical concerns, including decisions about vaccinations, medications and other treatments, you should always consult a healthcare professional.