Australia’s independent expert advisory group on vaccines is meeting to discuss fourth Covid-19 booster doses, as Omicron subvariants drive a rise in infections, leading some premiers to urge people to wear masks more widely.

The BA.4 and BA.5 strains of Omicron are becoming the dominant strains of Covid-19 in Australia, overtaking the BA.2 strain. A preliminary analysis estimates BA.4 and BA.5 to be about 36% more infectious than BA.2. This infectiousness is driving a new wave of disease, however, there is no indication the variants are more severe.

While Covid-19 vaccines do protect well against severe disease and death from the variants, they do not appear to be as effective at stopping infection and symptoms when it comes to the BA.4 and BA.5 strains.

The Australian Technical Advisory Group on Immunisation (Atagi), which advises the federal government about the national vaccination program, will need to factor in many issues: growing community cases, waning immunity from vaccination, a mix of immunity from vaccination and infection, the development of new, more targeted vaccines and when these may be available, and the ability of BA.4 and BA.5 to evade existing vaccines, as they consider whether to recommend widespread rollout of a fourth dose.