People who have recovered from COVID-19 and been vaccinated against the virus have the best and longest-lasting protection against future infection compared to people who were only vaccinated or only previously infected, according to a new international study.
The findings are published in the Lancet Infectious Diseases.
Niklas Bobrovitz
“These findings highlight the importance of vaccination, even for people who have already had SARS-CoV-2 infection, and may also inform planning and policies for future booster injection campaigns,” says researcher and lead author Niklas Bobrowitz, student in the MD program at the University of Toronto Temerty Faculty of Medicine.
The study looked at the effect of infection with COVID-19 or vaccination versus the combination of infection and vaccination (known as hybrid immunity) against future infection with COVID-19, hospitalization and severe illness. Researchers are also looking at how long protection lasts after the most recent infection or vaccination.
The findings show that people with hybrid immunity, which includes a full primary dosing regimen that varies by manufacturer, are well protected from hospitalization or severe illness for at least nine months, with less but still significant protection against reinfection .
The team found that prior infection and hybrid immunity provided more robust and longer-lasting protection against the Omicron variant than vaccination alone. And although protection against infection wanes quickly after infection or vaccination (60% reduced chance of infection at six months), protection against hospitalization or severe illness remains high (97% reduced chance of hospitalization or severe illness at 12 months).
To arrive at their findings, the team systematically reviewed 11 studies that examined people who had previously been infected, as well as 15 studies that included people with hybrid immunity.
The study, which is the most comprehensive study of hybrid immunity to date, is part of SeroTracker, a group that tracks population immunity around the world using serological test results that show antibodies to COVID-19 in a person’s blood from vaccination or infection. The platform was created by Canadian graduate and professional students and launched at the start of the pandemic.
Bobrowitz first got involved with SeroTracker at the invitation of his classmate Tingting Yan, one of the platform’s creators, who at the time was in his second year of the MD program and completing a master’s degree at the Institute of Health Policy. , Management and Evaluation at the Dalla Lana School of Public Health.
Having recently completed a PhD in clinical epidemiology at the University of Oxford, Bobrowitz wanted to use her research skills to help protect the public from the effects of COVID-19.
SeroTracker caught the attention of the Public Health Agency of Canada and the World Health Organization (WHO), who used the platform to develop models of the spread of infection. The project launched Bobrowitz working with researchers from around the world, including Maria Van Kerkhove, the WHO’s top technical advisor on COVID-19, and members of the Canadian Task Force on COVID-19.
The team also included contributions from trainees at universities in the United States and Canada, including Brianna Cheng and Christian Cao, both in their first year of Temerty Medicine’s MD program, and Xiaomeng Ma, a doctoral student in the Dalla School of Public Sciences Lana Hello.
Although the team’s findings suggest that hybrid immunity offers a greater protective benefit than vaccination alone, Bobrowitz emphasizes the importance of avoiding infection.
“Despite how much scientists and doctors have learned about COVID-19, it’s still very difficult to predict how an infection will affect different people,” says Bobrowitz. “Intentional contamination can result in death, the need for mechanical ventilation in the intensive care unit, or a host of serious chronic health consequences. It’s not worth the risk.”
Bobrowitz says that in addition to providing lessons for managing COVID-19 in the future, the study’s results may also have implications for outbreaks of other infectious diseases.
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