Prior Covid offers less protection vs Omicron; mRNA booster shot efficacy declines within months

The following is a summary of some recent studies on Covid-19. They include research that warrants further study to corroborate the findings and that has yet to be certified by peer review.

Previous Covid-19 less protective against Omicron variant

The immune response to Covid-19 helps protect against reinfection, but that protection is weaker against Omicron than it was against earlier variants of the coronavirus, according to new data.

A previous SARS-CoV-2 infection protects against Omicron reinfection only 56% of the time, researchers found in a review of national data in Qatar. Having had Covid was 90.2% effective against reinfection with the Alpha variant, 85.7% effective against a Beta variant reinfection, and 92% effective against Delta reinfection, researchers reported on Wednesday in The New England Journal of Medicine.

As was the case with reinfection due to earlier variants, however, "the protection of previous infection against hospitalization or death caused by reinfection (with Omicron) appeared to be robust," they said. In cases of reinfection with Omicron, for example, the immune response to previous infection was 87.8% effective at preventing the second infection from progressing to severe or critical illness or death.

mRNA vaccine booster protection declines within months

Protection provided by booster shots of the mRNA vaccines from Moderna Inc (MRNA.O) or Pfizer Inc (PFE.N) and partner BioNTech SE starts waning quickly, according to data published in Friday's Morbidity and Mortality Weekly Report from the U.S. Centers for Disease Control and Prevention (CDC).

Researchers reported that within two months after the second dose of an mRNA vaccine during the surge in infections caused by the Delta variant of the virus, vaccine efficacy was 94% against hospitalisation and 92% against emergency department or urgent care (ED/UC) visits. Efficacy waned thereafter, but climbed to 96% and 97%, respectively, at two months after a booster shot. Four months later, however, that protection had declined to 76% and 89%. Once Omicron became predominant, vaccine efficacy was 71% against hospitalisation and 69% against ED/UC visits within two months after the second dose, 91% and 87% at two months after a booster, and 78% and 66% four months later. The estimates are drawn from analyses of 241,204 Covid-related ED/UC visits and 93,408 hospitalisations between August and January.

"Our findings suggest that additional doses (of vaccines) may be necessary," Brian Dixon of the Regenstrief Institute and Indiana University said in a statement. "We also found that people who are Hispanic or Black are half as likely to have a third vaccine dose than people who are white, making (them) more vulnerable to severe Covid."