Omicron's risk of reinfection higher, but boosters still provide significant protection, state's chief medical officer says

As omicron spreads wildly out of control in Oklahoma and overwhelms hospitals, the state’s chief medical officer emphasized COVID-19 vaccinations and booster shots do significantly help protect against infection by the latest variant.

Dr. Gitanjali Pai said Wednesday that studies show the risk of reinfection with omicron is higher than for previous variants. Pai said current vaccines are still effective against omicron if antibody levels are high enough — even with so many mutations to the spike protein.

The virus’s spike protein attaches to human receptors and is the target of the vaccines to recognize the invaders and engage the body’s immune response against them.

“While we may expect that this variant might evade antibodies to some extent, it will likely still remain vulnerable to immune cells that destroy it once it enters the body,” Pai said.

Pai explained those two layers of protection that make omicron less likely to completely evade immunity.

First are antibodies already circulating in your body to defend against the virus colonizing your healthy cells. Secondly, there are T-cells — or immune cells — that mobilize to destroy infected cells after an infection occurs.

“With prior variants, it has been noted that as long as the levels of antibodies were high enough, a variant specific booster or vaccine did not seem necessary in those scenarios,” Pai said. “And so having enough such antibodies will still reduce the risk from infection, replication and spread.”

The Centers for Disease Control and Prevention released multiple studies Friday that demonstrate the continued protective value of vaccination against COVID-19 as omicron became the dominant variant in the U.S.

A third dose of vaccine was found to be “highly effective” during both delta and omicron surges at preventing COVID-19 emergency room or urgent care visits — 94% and 82%, respectively — and hospitalizations — 94% and 90%, respectively.

The study examined nearly 223,000 encounters from 383 emergency departments and urgent care clinics, as well as nearly 88,000 hospitalizations from 259 hospitals of adults in 10 states.

Vaccine effectiveness also was “significantly higher” among patients who had received their second dose of mRNA vaccine less than 180 days before medical encounters compared with individuals who had been vaccinated at least 180 days earlier.

“These findings underscore the importance of receiving a third dose of mRNA COVID-19 vaccine to prevent both moderately severe and severe COVID-19, especially while the Omicron variant is the predominant circulating variant and when the effectiveness of 2 doses of mRNA vaccines is significantly reduced against this variant,” the study’s authors wrote.

In another CDC study, vaccine effectiveness with respect to preventing cases was observed to be higher against omicron in people who were fully vaccinated and boosted than those who were only fully vaccinated.

The booster’s added benefits were “especially prominent” among ages 50-64 and 65 and up.

The study looked at data from 25 state and local health departments.

In a study published in the Journal of the American Medical Association that was led by CDC researchers, three doses of mRNA vaccine versus unvaccinated individuals corresponded to an estimated effectiveness against infection of 67.3% for omicron.

The three mRNA doses were found to be about 93.5% effective against infection by delta.

More than 70,000 tests across 49 states were evaluated.