ba.5 and ba.2.25: what do these omicron strains mean?

there are a number of omicron strains identified, with confusing names like ba.5 and ba.2.75. learn about the most talked-about strains.

by emma jones

published aug 04, 2022

last updated feb 16, 2023

3 minute read

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3 minute read

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ba.5 and ba.2.25 — what do these omicron strains mean?

knowing about all the covid-19 variants can get confusing and overwhelming. getty

omicron is currently the only circulating covid-19 variant of concern identified by the who. however, that doesn’t mean it’s simple to follow. there are a significant number of strains identified within it, with confusing names like ba.5 and ba.2.75, often leading to sub-sub strains that also have unique characteristics. here is a look at the most talked-about families of omicron.

what are the symptoms of omicron?

symptoms of omicron are similar to other variants of covid-19 and include a runny nose, cough, sore throat and fatigue that can progress to fever, headaches and muscle pain, according to uc davis.

patients infected with covid-19 during the omicron wave are less likely to report loss of taste and smell, and instead are more likely to report classic flu-like symptoms of cough and a sore throat, according to data from the u.k.

omicron ba.5 can evade vaccination

initially sequenced before variant ba. 4, ba. 5 was discovered in mid-november 2021. having been reported in at least 107 countries, this strain accounted for almost 70 per cent of sequenced cases at its peak in the summer and continues to have a strong global presence. ba.5 is more similar to the previous ba.2 strain than the original ba. 1 strain, with some researchers believing it actually evolved from the circulating ba.2 virus.

ba.5 is a slippery bugger, able to evade immunities from vaccination and even previous omicron infection. thankfully these “breakthrough” infections seem to be much more mild than previous waves, although they still pose a serious risk to the immunocompromised.

research regarding this wave is still ongoing so it’s difficult to understand how it differs from previous strains, but a preliminary study from portugal suggests it does not cause severe illness more often than the ba.1 strain. a similar study from south africa showed a lower death rate in those affected with this strain rather than previous ones.

vaccinations are slightly less effective against ba.5 than for previous strains, but continue to play an important role in guarding against severe illnesses. one preprint study (meaning the data hasn’t yet been reviewed by an independent party) from portugal found that the booster was associated with a 77 per cent reduction in risk of hospitalization from the ba.5 variant compared to 93 per cent for the ba.2 variant, and an 88 per cent reduction in risk of death from ba.5 compared to a 94 per cent reduction for ba.2.

“variant of interest”: omicron ba.2.75

also dubbed centaurus, because ba.2.75 doesn’t quite roll off the tongue, this variant started to take off at the beginning of the summer, but most recent data shows that it has dropped off. but because of the sudden surge health bodies are still watching it closely and have dubbed it a “variant of interest,” rather than a “variant of concern.”

preliminary data from india, where the virus had most of its presence, also didn’t show a significant connection between this variant and to hospitalizations or death rates, according to ctv news.

omicron ba.2 not so prevalent

surfacing towards the end of october 2021, this variant was predominately found in europe. after peaking in the spring of 2022, this variant’s presence has dropped significantly.

omicron ba.1 peaked in early 2022

discovered as early as september 2021, the ba.1 variant was 2.7 to 3.7 times more transmissible than the delta variant, according to forbes. this variant rapidly spread around the globe and was identified in 172 countries while predominately hitting the united kingdom and the us. its presence has dropped dramatically since its peak in early 2022.

while this variant was less severe than the delta strain, the fact that it spread so easily through communities meant there were still concerning spikes in hospitalizations and death rates, according to yale medicine.

it’s important to note that this data is not exact, as many health bodies have drastically scaled back testing and reporting strategies.

emma jones is a multimedia editor with healthing. you can reach her at emjones@postmedia.com or on instagram and twitter @jonesyjourn.

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ba.5 and ba.2.25: what do these omicron strains mean?