by Greg Lathan
Since the emergence of the initial Omicron variant late last year, COVID has increasingly become more infectious. Since then, multiple Omicron subvariants have emerged, with each new strain being much more transmissible than its predecessor. Omicron BA.5 and its sister, BA.4, currently account for more than 93% of all US covid cases, with BA.5 making up the vast majority of the two variants.
The rapid spread of BA.5 is likely due to its evasion of some of the immune defenses acquired by vaccinated individuals or those infected by earlier variants. Those who have managed to avoid COVID infection since it emerged in the US in early 2020 may discover it is difficult to continue their streak, with many who were infected by earlier Omicron subvariants contracting COVID a second time.
The BA.5 variant contain numerous mutations that alter the shape of their spike proteins, the studs on the surface of the virus that the pathogen employs to recognize and subsequently infect human cells. It appears that antibodies created in vaccinated individuals, which neutralize COVID by sticking to these spike proteins in older variants, do not recognize the altered studs on the surface of the newer subvariants. Therefore, the population of people who have been vaccinated, or those who have previously contracted COVID, have antibodies that are less potent at neutralizing BA.5. This trend will continue as other sub variants beyond BA.5 emerge. This process is called immune evasion and is the reason infection with an older strain of COVID (those predating the Omicron sub-variants) or those who contracted an earlier Omicron subvariant (BA.1/BA.2) have antibodies which are less effective at preventing reinfection with BA.5.
Immune evasion by BA.4 and BA.5 was documented by a large population study, which tracked all of Qatar’s COVID-19 cases since the emergence of BA.4/BA.5. The Qatar research team found that infection with a pre-Omicron variant prevented reinfection of BA.4 or BA.5 with an effectiveness of only 28.3%. Prior infection with an earlier variant of Omicron granted a significantly stronger immune response: nearly 80% effective at preventing BA.4 and BA.5 reinfection or nearly 3 times stronger than a prior infection with a pre-Omicron variant like Delta.
As more individuals become infected with the more recent Omicron strains of COVID, the possibility of new subvariants of Omicron also increases. The Centers for Disease Control and Prevention (CDC) is currently tracking a new ”variant of concern,” which has emerged in the US termed BA.4.6. The CDC designates COVID strains as “variants of concern” if they display greater transmissibility, reduced effectiveness of treatment, increased severity or decreased neutralization by COVID antibodies. BA.4.6 comprised 4.1% of nationwide COVID cases for the week ending July 30 and is high as 10% in certain midwestern states.
Presently there is not much data to determine if the emerging BA.4.6 variant is better than BA.4/BA.5 in evading immunity. A second variant, BA.2.75 was first detected in India in May, which has unofficially been termed Centaurus. Since then over 23 countries have documented BA.2.75. Ten US states have also identified this variant, however cases here remain relatively rare, with BA.2.75 currently comprising fewer than 0.5% of all US COVID cases.
The World Health Organization (WHO) is keeping a close eye on BA.2.75, but it is too early to ascertain whether this variant can spread or cause more severe disease than other Omicron variants. However, even if BA.4.6 and BA2.75 are not significantly worse than existing BA.4/BA.5 strains of Omicron, the speed at which new Omicron variants are emerging is alarming public health officials who are planning on new vaccine boosters this fall. These boosters would specifically target the Omicron variants, rendering vaccines in development less effective by the time of their release. For this reason, the White House is now pushing for universal COVID-19 vaccines that can target multiple variants simultaneously, which will be far more durable and provide much longer-lasting protection regardless of how the virus evolves. However, these universal COVID vaccines will not be ready for the public for at least another year.
Even with more specific COVID vaccines on the way, experts still encourage Americans eligible for another booster should get one NOW, as opposed to waiting until an Omicron specific vaccine arrives this fall. A study published August 2nd found that a second booster cut the rate of breakthrough infections of Omicron by 65% among Israeli health care workers.
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