A new mutation of the delta variant has been detected, but it may not be time to panic yet.
On Oct. 21, the UK health security agency (HSA) designated AY.4.2, a mutation of the B.1.617.2 delta strain, as a variant under investigation (pdf). The delta variant was first found in India in October 2020 and its AY lineage is found in about 70% of all samples sequenced.
Authorities are focused on it because cases with this mutation are rising in proportion to the highly transmissible original delta variant, from 3.8% in early September to nearly 6% by early October.
It is yet to be determined if AY.4.2 is more virulent or dangerous than the original. The variant has been found in 33 countries, including 20 cases in India, according to the Global Initiative on Sharing Avian Influenza Data.
For the large part, delta is still the dominant variant because of its high transmissibility and ability to slip through vaccines’ protective cover.
Is the AY.4.2 mutation more transmissible than delta?
All variants have mutations, but not all of those are alarming. As such there is nothing in the AY.4.2 mutation that is intrinsically dangerous, makes vaccines less effective, or causes more severe illness. Scientists say the spike protein mutations it exhibits have been found in other variants, too, but none of those was a variant of concern.
While it has not been proven to be significantly more transmissible, the AY.4.2’s secondary attack rate—the probability of an infection occurring in a group of people—in UK household settings is 12.4%. For the delta variant, it is 11.1%.
This means that in the same household, there are higher chances of an infection spreading if it has the AY.4.2 mutation.
For non-household settings, its secondary attack rate is almost similar to the original, possibly why the number of cases with AY.4.2. has not exploded yet.
Meaghan Hill, an epidemiologist at the UK’s HSA, tweeted saying it is likely that AY.4.2 may turn out to be slightly more transmissible, “slowly replacing delta infections” over the next few months.
Does AY.4.2 lead to more severe illness?
There is no clear indication from the UK that AY.4.2 leads to more severe illness, according to initial analyses based on emergency visits and hospitalisations.
“However, these analyses do not adjust for crucial factors that can influence outcomes such as age and vaccination status and should be interpreted with caution,” the UK HSA noted on Oct. 22.
This also means that the reasons for the mutation’s greater transmissibility are unclear: Is it the nature of the group in which these infections are rising (the elderly or the unvaccinated) or the region of its high prevalence?
Importantly, though, infections spread faster and cause severe disease in unvaccinated or partially vaccinated populations even with the delta variant. Vaccines are still highly effective in preventing hospitalisation and death.
Only further studies of AY.4.2 infections correlating with vaccination status and neutralising antibodies from past infection may tell us how much more dangerous it is.