- New Omicron variant, called XBB, spreading in Northeast US
- XBB able to evade antibodies from prior infection, vaccines, and monoclonal antibody treatments
- Vaccines may make people more susceptible to XBB and contribute to its rapid evolution
- XBB has evolved to elude antibodies induced by vaccines and breakthrough infections
- Bivalent vaccines reduce risk of getting infected by 30% while BA.5 variant spreading, but may be because workers who are more cautious are also more likely to get boosted
- Workers who received more vaccine doses at higher risk of getting sick: 3.4 times as likely to get infected with three more doses, 2.6 times as likely with two
A new variant of the coronavirus, called XBB, is spreading rapidly in the Northeast United States, according to public health experts. Some studies indicate that this variant is as different from the original virus strain, which originated in Wuhan, as the 2003 SARS virus.
It is not yet known if XBB is more deadly than other variants, but it has mutations that allow it to evade antibodies produced by prior infections and vaccines, as well as existing monoclonal antibody treatments, according to a Wall Street Journal publication.
There is also growing evidence that repeated vaccinations may make people more vulnerable to XBB and potentially contribute to the rapid evolution of the virus.
Prior to the emergence of the Omicron variant in Nov 2021, there were only four other variants of concern: Alpha, Beta, Delta, and Gamma.
Of these, only Alpha and Delta caused global outbreaks.
However, Omicron has spawned numerous descendants, many of which have appeared in different regions of the world and share some of the same mutations.
“Such rapid and simultaneous emergence of multiple variants with enormous growth advantages is unprecedented,” according to a study published in the journal Nature.
The virus appears to have developed mutations that enable it to transmit more easily and escape antibodies elicited by vaccines and prior infections under selective evolutionary pressures.
The Nature study suggests that the process of “immune imprinting” may be contributing to the evolution of the virus. Vaccines are designed to train the immune system to remember and fight off the original Wuhan strain.
However, when new and significantly different strains emerge, the immune system may not respond as effectively.
Bivalent vaccines, which target both the Wuhan and BA.5 variants, stimulate the immune system to produce antibodies that target common regions of the two strains.
In evolutionary terms, mutations that allow the virus to evade these common antibodies are more likely to survive and thrive, making the virus “fitter.”
XBB has evolved to elude antibodies induced by vaccines and prior infections.
Therefore, the Nature study suggests that “current herd immunity and BA.5 vaccine boosters may not efficiently prevent the infection of Omicron convergent variants.”
A study published in the New England Journal of Medicine last month provides further evidence of the vulnerability caused by immune imprinting.
Neutralizing antibodies in people who received the bivalent vaccine were 26 times as high against the original Wuhan strain as they were against XBB and four times as high as they were against Omicron and the BA.5 variant.
Similarly, a study published in the journal Cell this month found that antibody levels in people who received four shots were 145 times as high against the original Wuhan strain as they were against XBB.
While a bivalent booster slightly increased antibodies against XBB, experts claim that boosters improve protection against this variant.
A Cleveland Clinic study tracked the health of its healthcare workers and found that bivalent vaccines reduced the risk of infection by 30% while the BA.5 variant was spreading.
However, the study also found that workers who received more doses were at a higher risk of getting sick.
Those who received three or more doses were 3.4 times as likely to get infected as the unvaccinated, while those who received two doses were only 2.6 times as likely.
“This is not the only study to find a possible association with more prior vaccine doses and higher risk of COVID-19,” the authors of the Cleveland Clinic study noted.
“We still have a lot to learn about protection from COVID-19 vaccination, and in addition to a vaccine’s effectiveness it is important to examine whether multiple vaccine doses given over time may not be having the beneficial effect that is generally assumed.”
