Previous Covid-19 less protective against omicron variant, reports Reuters.
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 per cent of the time, researchers found in a review of national data in Qatar. Having had Covid was 90.2 per cent effective against reinfection with the Alpha variant, 85.7 per cent effective against a Beta variant reinfection, and 92 per cent 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 hospitalisation 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 per cent 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 or Pfizer Inc and partner BioNTech SE starts waning quickly, according to data published in Friday's Morbidity and Mortality Weekly Report from the US 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 per cent against hospitalisation and 92 per cent against emergency department or urgent care (ED/UC) visits. Efficacy waned thereafter, but climbed to 96 per cent and 97 per cent, respectively, at two months after a booster shot. Four months later, however, that protection had declined to 76 per cent and 89 per cent. Once omicron became predominant, vaccine efficacy was 71 per cent against hospitalisation and 69 per cent against ED/UC visits within two months after the second dose, 91 per cent and 87 per cent at two months after a booster, and 78 per cent and 66 per cent 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."