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The first large study of this type found that people over the age of 65 were at high risk, but reinfection with SARS-CoV-2 was still rare.
Researchers analyzed the test results of 4 million people infected with COVID-19 in Denmark and found that less than 1% experienced reinfection.
The initial infection was associated with approximately 80% of the overall protection against recurrence of SARS-CoV-2. But among people over the age of 65, protection plummeted to 47%.
Dr. Daniela Michel Meyer
“Not everyone is protected from reinfection after the initial infection. Older people are at increased risk of reinfection,” said co-author Dr. Daniela Michelmeyer. Medscape Medical News.. “Our findings emphasize the importance of policies to protect the elderly, even if previously infected with COVID-19, and the importance of adhering to infection control measures and restrictions. “
Confirmation of the need for vaccination
“The findings also highlight the need to vaccinate people who previously had COVID-19 because of the unreliable innate immunity to infection, especially among older people aged 65 and over.” Michlmayr, a researcher at the Department of Parasitology, added. A fungus of Staten Serums Institut in Copenhagen, Denmark.
Population-based observational studies Published online March 17 Lancet..
Dr. David Hirschwerk
“The findings make sense. Immunodeficiency Or older people may not initiate a long-lasting immune response, “said Dr. David Hirschwerk. Medscape Medical News When asked to comment. “Even if previously infected with COVID, it emphasizes the importance of vaccination for older people.
“For those who were infected last spring and haven’t been vaccinated yet, this confirms the value of continuing to pursue the vaccine,” said Hirschwerk, an infectious disease specialist at Northwell Health in Manhasset, NY. It’s useful, “he added.
Evidence of reinfection risk was limited prior to this study. “Little is known about protection against repeated SARS-CoV-2 infections, but two studies in the United Kingdom show that immunity can last at least 5-6 months after infection,” the authors said. Have stated.
Co-authors Christian Holm Hansen, PhD, Michlmayr and colleagues found that 2.11% of 525,339 people were SARS-CoV-2 positive during the first surge in Denmark between March and May 2020. discovered. The second surge from September to December.
By the end of 2020, more than 10 million people had undergone a free polymerase chain reaction test through the Danish government or the national TestDenmark program.
Dr. E. John Welly
“My overall view is that it’s great to be able to see this question on such a large dataset,” E. Dr. John Welly said. Medscape Medical News.. The findings support “what we saw in previous small studies.”
Wellie, director of the Institute of Immunology at the University of Pennsylvania in Philadelphia, Pennsylvania, added that nature maintenance against about 80% of reinfections is “not as good as a vaccine, but not bad.”
Does age change immunity?
“Our finding that older people are more likely to be positive than younger people can be explained by the natural age-related changes in the elderly’s immune system, also known as immune aging. “The author states. ..
The researchers found no significant difference in reinfection rates between women and men.
Similar to previous studies, this study also shows that the first attack of SARS-CoV-2 infection appears to provide protection for at least 6 months. The researchers found no significant difference between those who were followed for 3-6 months and those who were followed for more than 7 months.
Variants not included
To explain possible biases among people who were repeatedly tested, Michlmayr and colleagues performed a sensitivity analysis in a subgroup. They assessed the reinfection rate of people who were tested frequently and regularly (nurses, doctors, social workers, medical assistants), with 1.2% positive on the second test during the second surge. I found that.
The limitation of this study was the inability to correlate symptoms with the risk of reinfection.Also, the researchers did not explain SARS-CoV-2 variant“During the study, such variants were not yet established in Denmark, although this pattern changed in 2021.”
Hirschwerk was asked to speculate on whether the results would be different if the mutations were considered in the study, “depending on the mutation, but certainly for the B.1.351 mutation, the risk of reinfection with SARS-CoV-. There are already data that clearly show that. 2 Despite previous infections with the original strain of the virus. “
The emergence of SARS-CoV-2 mutants of concern that may escape innate and vaccine-related immunity “complexes the problem.” Rosemary J. Boyton (MBBS) and Daniel M. Altman (PhD) of Imperial College London, London, UK, wrote: Accompanying comments To The lancet.
“Newly concerned variants may shift immunity below the protective margin and drive the need for the latest vaccines. Interestingly, in individuals with a history of SARS-CoV-2 infection, The vaccine response is significantly enhanced even after a single dose, “they add.
In the current study, “the hope of protective immunity from natural infections may be out of our reach, and a global vaccination program with high-efficiency vaccines is a permanent solution.” Boyton and Altman said.
What causes the alarm?
Despite evidence that reinfection is relatively rare, “many people will find that the data reported by Hansen and colleagues about protection against natural infections is relatively alarming,” Boyton said. Altman wrote in their commentary. The 80% protection rate from common reinfections and the 47% rate among people over the age of 65 are “more interested in numbers than provided by previous studies.”
The vaccine appears to be superior in quality, quantity and durability of protection against recurrent infections as measured in terms of neutralizing antibodies and T cells compared to previous infections with SARS-CoV-2, Boyton, and Altmann. ..
Need more research
The period of nature maintenance against reinfection is an open issue, “because too little time has passed since the pandemic began,” the researchers say.
The authors state that future prospective and longitudinal cohort studies in combination with molecular surveillance are needed to characterize antibody titers and diminished protection against recurrent infections. In addition, more answers are needed on how some viral variants contribute to the risk of reinfection.
No funding for the study has been reported. Michlmayr, Hirschwerk, Wherry, Boyton, and Altmann do not disclose the relevant financial relationships.
Lancet.. Published online on March 17, 2021. Full text, comment
Damian McNamara is a Miami-based staff journalist. He covers a wide range of medical specialties, including infectious diseases, gastroenterology and neurology. Follow Damian on Twitter: @MedReporter..
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