The protection from prior COVID-19 infection doesn’t protect well against reinfection of an Omicron coronavirus subvariant, according to a new study.
The protection, known as natural immunity, was estimated at just 6 percent against reinfection with BA.2.75, the Omicron subvariant, by researchers in Qatar, where the subvariant is the dominant virus strain.
Natural immunity offered better protection if a person was infected during the Omicron era, which started in late 2021.
People who contracted BA.1 or BA.2 had 49.9 percent protection against reinfection. People who contracted BA.4 or BA.5 had 80.6 percent protection against reinfection.
People who were initially infected during the pre-Omicron era and then infected again with BA.1 or BA.2 had 56.4 percent protection, and people who were initially infected during the pre-Omicron era and then infected again with BA.4 or BA.5 had 91.6 percent infection.
“A combination of pre-omicron and omicron immunity is most protective against BA.2.75 reinfection,” the researchers said.
They utilized national COVID-19 databases, which include the results of all tests conducted at health care facilities in Qatar.
Pre-Omicron infection also doesn’t protect well against reinfection against BA.4 and BA.5, the researchers said in a separate study published in October.
Pre-Omicron infection effectiveness against symptomatic BA.4 or BA.5 reinfection was just 35.5 percent, and the effectiveness against any BA.4 or BA.5 reinfection regardless of symptoms was 27.7 percent.
On the other hand, the effectiveness of Omicron infection against BA.4 or BA.5 reinfection was 76.2 percent (symptomatic) and 78 percent (regardless of symptoms).