On 26th November 2021, the World Health Organization declared Omicron to be a COVID-19 variant of concern based on preliminary evidence which showed it is able to spread quickly. As Omicron is still new, we are learning more about how it behaves each day and experts around the world are monitoring it closely to see how it will affect the pandemic. RCPA Fellow Professor Dominic Dwyer is a Medical Virologist and Infectious Diseases Physician, and he explains what we know so far about the Omicron variant.

We had our first importation of Omicron into Australia (Sydney) on 23rd November 2021 and since then, cases have been identified in NSW, ACT, QLD and VIC. Early data suggests that Omicron spreads more quickly than the Delta variant, certainly as seen in Southern Africa, but whether this is the same in other countries is yet to be determined. There are factors in Southern Africa that may make transmission easier i.e., less people are vaccinated, the medical system may be problematic, and there is a different underlying burden of diseases such as HIV and tuberculosis.

At the moment, children and younger adults seem to account for many of the Omicron cases and the illness seems to be mild or asymptomatic. However, as the data is limited, it is still too early for us to say for sure. In most places, this age group in general is not vaccinated or is under vaccinated, especially in some countries of the world where vaccination rates are not good. This could explain why we are seeing more cases in this age group.

So far, the evidence shows that our routine PCR tests will pick up the Omicron variant and at this stage we are reasonably happy that we can diagnose Omicron infection. As the mutations in the spike region of the Omicron variant are different to the Delta variant, we perform another test to confirm whether it is Omicron after receiving a positive PCR result. The S gene is not detected in people with Omicron, whereas with Delta it is, it is a way of screening between the two, said Prof Dwyer.

Australia has one of the highest vaccination rates in the world with around 75% of the population fully vaccinated. However, with the emergence of Omicron, one of the main questions has been whether or not the current vaccines will provide good protection. Whilst medical advice suggests the Omicron variant is likely to be more transmissible, there is emerging evidence vaccines will provide protection.

As with previous COVID-19 variants, vaccination does not stop someone from getting infected with Omicron, but it does seem to have an effect on the severity of disease. People who have been vaccinated who get Omicron generally have much milder illness and may not even be aware that they have been infected. So far, the proportion of people ending up in hospital or the proportion of older people getting seriously ill seems to be low but again, the data is not all there yet.

Certainly, in the laboratory, it looks as though vaccine efficacy may be slightly reduced against Omicron, but preliminary evidence suggests that boosters have a positive benefit. It is therefore important that people go and get their boosters when they are eligible. Whether that protection is less or the same as we had for Delta or some of the other variants is uncertain at this stage, but we are finding our way through that, said Prof Dwyer.