COVID-19

What is it?

COVID-19 disease is caused by infection with the SARS-CoV-2 virus of which there are many different strains and subvariants.  In 2024, the Omicron variant is the predominant strain circulating globally. 

Since its emergence in 2019, COVID-19 disease has had vast impacts on society. In addition to the public health implications, the economic, social and mental health effects have been and continue to be significant.   

What to look for?

Infections can be asymptomatic or can result in a spectrum of symptoms, from mild respiratory symptoms to more serious disease affecting multiple organs and systems. Severe disease can lead to hospitalisation, mechanical ventilation, and can be fatal.    

Common symptoms of acute infection can include rhinorrhoea (runny nose), sneezing, headache, sore throat and fatigue. The symptoms of fever, loss of smell or taste and persisting cough seen in infections with previous variants (Alpha, Beta, Gamma, Delta) are less likely to occur in infections with the Omicron variant. 

Long COVID is a chronic condition that can occur following acute infection. It is the persistence of symptoms for greater than 3 months after an initial infection that cannot be attributed to other causes. Long COVID can have a huge impact on an individual’s quality of life, mental health and ability to participate in work or schooling. Long COVID is more common in people who have experienced severe COVID-19 disease, those who had underlying medical conditions prior to infection (e.g. hypertension, chronic lung disease, diabetes, obesity) and those who are unvaccinated.  

Paediatric Multisystem Inflammatory Syndrome Temporally associated with SARS-CoV-2 (PIMS-TS), or Multisystem Inflammatory Syndrome in Children associated with COVID-19 (MIS-C), is a newly described condition that has been reported in children in the first 2-6 weeks after COVID-19 infection. It is an inflammatory condition, similar to Kawasaki disease, and is characterised by rash, fever, shock and abdominal pain. Children experiencing PIMS-TS almost always require hospitalisation for treatment.

How is it transmitted?

COVID-19 is transmitted through the inhalation of virus particles made airborne when an infected person coughs, sneezes, breathes, speaks or sings. Droplets containing virus particles can contaminate surfaces and can be spread when a person touches these surfaces and then touches their nose, mouth or eyes. Poorly ventilated settings can also contribute to the spread of COVID-19 because aerosol particles can remain suspended in the air for several hours longer than in well-ventilated settings. 

The incubation period for the disease is 1 to 14 days, with most individuals displaying symptoms 3 days after being exposed. Individuals are most infectious in the 2 days before their symptoms begin and the early stages of their illness. People with asymptomatic disease can still infect others.   

Epidemiology

Since 2019, over 774 million infections have been reported worldwide contributing to more than 7 million deaths. True figures are likely to be much higher. Serosurveys indicate that by December 2022 more than two thirds of adult Australians had been infected with SARS-CoV-2.

Individuals with immunocompromise, advancing age (particularly > 70 years), obesity, respiratory conditions, heart disease, diabetes, renal disease, liver disease, neurological conditions and disability are more likely to experience severe symptoms if infected with SARS-CoV-2. Pregnancy in unvaccinated people is also recognised as a risk factor for developing severe disease; however, this risk has declined substantially since the Omicron variant became the predominant circulating strain. 

Certain occupations, such as working in healthcare, increase likelihood of exposure to SARS-CoV-2 and therefore infection.   

Prevention

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

While natural infection does provide some immunity, it is not lifelong, and the emergence of newer strains contributes to repeat infections. 

Vaccination aims to reduce the severity of COVID-19 symptoms and the need for hospitalisation. There are 2 vaccine brands available for use within Australia:  

• Comirnaty (Pfizer) vaccine containing nucleoside-modified mRNA encoding the spike glycoprotein of SARS-CoV-2   
• Spikevax (Moderna) vaccine containing nucleoside-modified mRNA encoding the spike glycoprotein of SARS-CoV-2   

As newer variants of the SARS-CoV-2 virus emerge, vaccines are updated to target the strains that are circulating; where possible, these should be used preferentially. 

Table 1: Vaccine brands and type available for use by age group

shaded boxes indicate that vaccine is not available for use in this age group.
shaded boxes indicate preferred vaccines in this age group.
✓ may be used in this age group.
* Comirnaty (Pfizer) Omicron XBB.1.5 is registered for use in individuals aged 6 months to 4 years and supply is anticipated in early 2024. When stock of this formulation becomes available this vaccine will be preferentially recommended in this age group over the Original [Maroon cap] vaccine.

Primary course

Immunocompetent people aged 5 years and over require a single dose of vaccine to complete their primary course.

People aged 6 months and over with severe immunocompromise, and children aged 6 months to 4 years with increased risk of severe disease, require 2 doses, 8 weeks apart. A 3rd dose may be considered based on individual circumstances.

Further doses

Following receipt of a primary course, recommendations for further doses vary depending on the age of the individual and their risk factors for severe disease.  

Table 2: 2024 recommendations for COVID-19 booster doses (adapted from ATAGI statement on the administration of COVID-19 vaccines in 2024)

shaded boxes indicate that vaccine is not available for use in this age group.

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. 

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 and 24 years following a second dose of vaccination. Pericarditis occurring after vaccination is more common in the 20 to 45 year old age group for both males and females. 

Thrombosis with thrombocytopenia (TTS) was a rare condition that was reported to occur in people who had previously received the COVID-19 vaccine Vaxzevria (AstraZeneca). Since March 2023, Vaxzevria is no longer available for use in Australia.

Commonly asked questions

Resources

• MVEC: Vaccine platforms 
• MVEC: Immunosuppression and vaccines
• Victorian COVID-19 vaccine safety report
• ATAGI clinical guidance on COVID-19 vaccine administration errors
• Australian Government Department of Health and Aged Care: International COVID-19 vaccines recognised by Australia
• Australian Immunisation Handbook: COVID-19
• CDC: Long COVID or post COVID conditions