COVID-19 booster jabs provide protection against Omicron variants

A new study by researchers at the University of Washington School of Medicine in Seattle and the Howard Hughes Medical Institute, both US has found that current vaccine boosters may provide sufficient immune protection against severe Omicron-induced COVID-19 disease. The research, which was recently published in Science, studied a comprehensive panel of vaccines available in the United States and around the world, as well as immunity acquired through previous infection.

This study’s results are consistent with other research evidence that a third vaccine dose expands existing memory B cells in our bodies specific for the surface protein mediating entry into cells (called the spike protein) of the SARS-CoV-2 pandemic coronavirus, as well as inducing new memory B cells. This leads to production of antibodies with enhanced potency against the Omicron subvariants.

The scientists first examined the functional impact of the mutations in the Omicron subvariants spike proteins – the machinery on the virus that both gives it its crown-like appearance and enables it to attach to, fuse with, and infect cells. They found that the ability of the Omicron BA.5 spike to bind with its host receptor (ACE2) was more than six times stronger than the ancestral SARS-CoV-2 strain.

In contrast, all Omicron subvariants were slower at the next major step after binding with the receptor: fusing with the membrane on the host cell. The stronger binding might help the subvariants compensate for their diminished capacity to fuse with the host cells, the scientists hypothesise.

The researchers then evaluated, in human plasma samples, the neutralising activity, elicited by vaccines or by prior infection, against the various Omicron subvariants. Some of the samples came from individuals who had COVID-19 very early on in the pandemic before vaccines were available. Only five of these 24 early pandemic individuals had detectable neutralising activity in their plasma against any of the four Omicron sub lineages tested. Even then, their response was very weak.

The researchers noted, “Overall, the data underscores the magnitude of evasion of polyclonal plasma neutralising antibody responses for Omicron sub lineages.”  They added that there was “a subtle but consistently more marked effect for BA.1 and even more so for BA.4/5 compared to BA.2 and BA.2.12.1” The findings help confirm that the soon-to-be globally dominant BA.5 will be the most immune evasive SARS-CoV-2 variant to date.

Based on their findings, the researchers observed, “The marked improvement in plasma neutralising activity for subjects that received a booster dose over those that did not highlights the importance of vaccine boosters for eliciting potent neutralising antibody responses against Omicron sublineages.” Thus, despite the high degree of Omicron subvariant immune escape, added booster doses with currently available vaccines will likely offer strong protection against severe disease.

Additional preliminary observations from this study suggest that the time interval between immunisations with certain available vaccines may affect the breadth and strength of the virus neutralising responses.  The researchers also think that the availability of several different vaccines might help in creating a more robust cross-reactive cellular immunity against Omicron subvariants.

They also called for repeatedly evaluating the ongoing effectiveness of current vaccines and sustaining efforts to develop and test new vaccines and new vaccine strategies against the pandemic coronavirus and other related viruses.