ORIGINALLY POSTED MARCH 11, 2022
News reports today and last night address a recent increase in COVID-19 numbers reported in NSW and that modelling suggests we can expect a doubling of cases over the next week or two.
This is due to the Omicron sub-lineage BA.2 outcompeting the previous dominant Omicron BA.1 and BA.1.1 sub-lineages.
There is no evidence that BA.2 causes more severe disease than the previous Omicron, but it is more transmissible, hence the out-competition of its predecessors.
The BA.2 version caused a large outbreak in Denmark and studies there showed that it was at least 10% more transmissible than BA.1 in household settings.
In the highly vaccinated population there, the household attack rate was 29% for BA.1 and 39% for BA.2. Those who were booster vaccinated or recently fully vaccinated were still less likely to contract the virus and to transmit it to others.
The global reported transmission numbers are continuing to come down but some areas, including Australia now, have increases due to the new variant and its sub-lineage.
Infection with previous variants such as Delta, offer poor or no protection against BA.2, but BA.1 infection offers protection, at least for now, but re-infection is still possible and has been documented and reported by the WHO.
Increased community transmission increases exposure probabilities and the likelihood of requiring isolation.
Continued protective measures (masks, hand hygiene, physical distancing, and asymptomatic testing) help to reduce the risk.