Omicron BA.3 variant: symptoms of Covid subvariant, how contagious is it and does it cause severe illness?

The World Health Organisation (WHO) has said it is tracking several sub lineages of the Omicron strain of Covid, including BA.1, BA.1.1, BA.2, and BA.3.

But what is Omicron BA.3 and can it cause severe disease?

What is BA.3?

Omicron was recently divided into three lineages, these being BA.1, BA.2, and BA.3.

All three lineages were first detected at approximately the same time and from the same place.

A study published in the Journal of Medical Virology titled ‘Emergence of Omicron third lineage BA.3 and its importance’ found that there were no specific mutations for the BA.3 lineage in spike protein.

Instead, it is a combination of mutations in BA.1 and BA.2 spike proteins.

What are the symptoms?

Common symptoms include a sore throat, runny nose, sneezing, headache, body ache and mild fever.

How contagious is it?

Omicron is considered to be the milder variant of Covid and during the third wave it was primarily caused by its subvariant BA.1. However, this variant has a rapid rate of transmission.

The three sub lineages of the Omicron variant were all detected from the same place and viruses that develop simultaneously and from the same place have equal chances of spreading worldwide.

The study found that of the 33 mutations in the BA.3 lineage spike protein, 31 mutations are common to BA.1.

It said: "BA.3 lineage caused the lowest number of cases in these three lineages. Therefore, it can be speculated that the reason for the BA.3 lineage spreading at very low speeds and causing fewer cases may have been due to the loss of six mutations from BA.1 or obtaining two mutations from BA.2.”

The study said Omicron has so far been thought to cause mild disease, but "it is also possible to develop some mutations" that can lead to serious illness.

Although all the three lineages have spread worldwide, the rate of spread of these three lineages is different.

The study added: "Of these three lineages, it is questionable why only BA.1 dominates much more than the other lineages. This is likely due to differences in mutations in the spike protein required for virus transmission and host cell entry," the study showed.”