Enduring an initial Omicron infection may not spare you from Omicron subvariants, according to preliminary data from South Africa.
The country is currently at the beginning of a new wave of infections, mainly driven by two subvariants of Omicron coronavirus, BA.4 and BA.5. Despite a massive wave of cases of the original BA.1 omicron variant in December that infected a large part of the country, new omicron cases rose 259 percent in the past two weeks, according to data tracking The New York Times. Hospital admissions have also increased, and deaths have risen by 18 percent.
Preliminary data posted online last week helps explain why cases are rising again – the BA.4 and BA.5 omicron subvariants can evade neutralizing antibodies generated by infections with BA.1. For the study, led by virologist Alex Sigal of the Africa Health Research Institute, researchers compared neutralizing antibodies from people infected with BA.1 to BA.4 and BA.5 in a lab. They had samples from 24 unvaccinated individuals who were infected with BA.1 and 15 vaccinated individuals who also had BA.1 infection (eight individuals had been vaccinated with the Pfizer/BioNTech vaccine and seven had the Johnson & Johnson Vaccine).
In the unvaccinated subjects, levels of neutralizing antibodies to BA.4 and BA.5 were 7.6-fold and 7.5-fold lower, respectively, compared to levels to BA.1. In vaccinated individuals, the fall was shorter: 3.6-fold and 2.6-fold lower than BA.4 and BA.5, respectively.
Although the study is small and the data is preliminary, the results suggest that the latest omicron subvariants can defeat protection provided by previous omicron versions. However, vaccination seems to weaken the advantage of the subvariants. The total neutralization values against BA.4 and BA.5 were five times higher in vaccinated than in unvaccinated subjects.
However, in places where vaccination coverage is low or where vaccination protection is falling, BA.4 and BA.5 could potentially trigger a new wave of cases, as seems to be the current situation in South Africa.
In the United States, where immunization coverage is relatively high but protection is declining, only small amounts of BA.4 and BA.5 have been found circulating. At the moment, another sub-variant, BA.2, is dominating and is causing an increase in cases. BA.2 is similar to BA.4 and BA.5 – BA.2 differs from BA.4 and BA.5 by only three mutations and one deletion in the critical spike protein of the virus.
But US experts are closely watching another subvariant, BA.2.12.1, which has a similar mutational profile to BA.2, but has two additional mutations. One of the mutations in BA.2.12.1 is in the same location as a unique mutation in BA.4 and BA.5 – amino acid position 452.
While BA.2 is still the dominant variant in the US, BA.2.12.1 is quickly gaining ground. Currently, BA.2 accounts for an estimated 68 percent of SARS-CoV-2 cases in the US and BA.2.12.1 accounts for an estimated 29 percent. according to the Centers for Disease Control and Prevention.
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