The extreme contagiousness of the Omicron variant which appeared at the end of 2021 has made cases of reinfection very commonplace. But are they really benign? That’s the question Ziyad Al-Aly’s team at the Veterans Health Center in St. Louis, Missouri, tried to answer in a study published in the journal NatureMedicine Thursday, November 10. And for the epidemiologist, the answer is clear: “Reinfection is not benign, it is better to avoid it. »
The main interest of their work, this study was conducted on the very large national health care database of the United States Department of Veterans Affairs of nearly 5.8 million people, including more than 443,000 people who were infected with the least once by Covid-19 and nearly 41,000 having been reinfected between 1er March 2020 and April 6, 2022. Their results show that reinfection with SARS-CoV-2 doubled the risk of death and tripled the risk of hospitalization and heart problems. The sequelae identified are numerous, including pulmonary, cardiovascular, hematological, diabetic, gastrointestinal, renal, mental, musculoskeletal and neurological disorders.
The risks increase with the number of infections
These risks were observed in both vaccinated and unvaccinated individuals, most pronounced at the time of infection, but up to six months later. “Even if a person had a previous infection and was vaccinated – that is to say, they benefited from a double immunity, that of the previous infection and that of the vaccines -, they are still susceptible to experience adverse effects if re-infected”, insists Ziyad Al-Aly. Moreover, the risks increase with the number of infections.
The severity of reinfections depends on the disease. Some provide persistent immunity over time, such as measles or chickenpox. Others make it possible to acquire an immunity which decreases over time; the impact of the virus will then depend on the state of health of the person or on the new strains in circulation, as is the case with the flu, whose health burden varies from one year to the next. Only dengue fever reverses the logic: a past infection can aggravate the consequences of a second encounter with the virus.
The results of the American team do not mean that people infected several times with Covid-19 are more seriously ill during their reinfections than during their first encounter with the virus. Studies have shown the opposite. The one led by Laith J. Abu-Raddad and published in July in the New England Journal of Medicine points out that people vaccinated with two doses and already infected once have, depending on the type of vaccine, 94% to 100% less risk of contracting a serious, critical or fatal infection. A priori, people infected and then vaccinated are therefore the best protected against the risk of a serious form.
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