Protection site

Hybrid immunity provides increased protection that lasts longer against Covid-19 reinfection, studies show

The studies offer greater insight into the concept of hybrid immunity: when previously infected people, who have “natural immunity”, then gain vaccine-acquired immunity.

A die studies, conducted outside Israel, found that among people who had recovered from Covid-19 infections, reinfections were more than four times more common among those who did not receive vaccines than among those who did. had done after the primary infection. However, the study, which involved more than 149,000 people with a history of Covid-19 infection, also found that the effectiveness of the Pfizer vaccine is lower in adults over 65. The vaccine was 82% effective in people aged 16 to 64 and only 60% effective in those 65 and older. This study was conducted between March 1, 2021 and November 26, 2021, encompassing the surge of the Delta coronavirus variant in Israel.
The study also found that there was no significant difference in vaccine effectiveness whether previously infected people received one dose or two doses, supporting evidence of other studies which showed that one dose was enough to protect people who had already been infected with Covid-19 from reinfection.

These results may have implications for vaccination policies.

Shane Crotty, a virologist and professor at the Center for Infectious Diseases and Vaccine Research at the La Jolla Institute for Immunology, told CNN it would be “quite reasonable” to have a policy in the United States. States that would oblige people who have already contracted coronavirus infections. a single dose of a vaccine, based on the results of this research. Crotty did not participate in either study.

Ronen Arbel, principal investigator of this study and health outcomes researcher at Clalit Health Services in Israel, believes that more countries should adopt a policy like the one the Israeli Ministry of Health implemented in March 2021, when he recommended a single dose of vaccine for people who had recovered from Covid-19, to be given three months after their primary infection.

“If you recovered from Covid-19, it’s like you got a primary shot,” Arbel told CNN. “You should get vaccinated, but once is enough. It’s kind of like a booster.”

The second new studyconducted in the UK, demonstrated that immunity is longer lasting and longer lasting in people who had recovered from Covid-19 infection before receiving a Pfizer vaccine.

Among participants who were not previously infected, two doses of the vaccine were associated with an 85% lower risk of infection two months after vaccination. However, this number would drop to 51% six months after vaccination. In contrast, those vaccinated after recovering from Covid-19 maintained over 90% protection over a year after primary infection and over six months after vaccination.

“Seeing the whole virus in one form or another producing broad immune responses with a deepening of the immune response with vaccination (before or after) may confer super immunity,” said Dr Monica Gandhi, deputy chief of the Division. of HIV, Infectious Diseases and Global Medicine at the University of California, San Francisco, who was not involved in either study.

The UK research used data from the SIREN study of healthcare workers. The more than 35,000 participants were followed between December 7, 2020 and September 21, 2021 and underwent PCR tests for Covid-19 every two weeks. It found that among previously infected people, the risk of re-infection was 86% lower than the risk of primary infection in unvaccinated people. However, this protection fell to 69% more than a year after infection, indicating that primary infection alone does not confer lasting immunity.

According to Crotty, hybrid immunity allows the body to create more diverse antibodies to neutralize a wider variety of variants. This also happens with a full vaccination and a booster, but it happens much faster with infection followed by vaccination.

“Hybrid immunity has a whole bunch of added bonuses. One that these studies are showing quite right now is durability. Durability is pretty robust,” Crotty said.

Although both studies add to growing evidence that hybrid immunity may offer increased protection against future Covid-19 infections, neither includes data on the rise of the highly transmissible variant of Omicron.

“The overall risk of being re-infected is much higher with Omicron than with Delta. Does the vaccine protect [against Omicron]? We can hypothesize that this is the case, but we don’t have the data yet,” Arbel said.