COVID reinfection is rare, but at greatest risk after age 65

March 18, 2021-The first major study of this kind was Coronavirus People over the age of 65 are at high risk, but reinfection remains rare.

Researchers analyzed the results of four million coronavirus tests in Denmark and found that less than 1% of people who tested positive experienced reinfection.

Initial infection was associated with an overall protection of approximately 80% against recurrence of COVID-19. But among people over the age of 65, protection plummeted to 47%.

“Not everyone is protected from reinfection after the initial infection. Older people are at increased risk of reinfection,” co-author Dr. Daniela Michelmeyer told Medscape. “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, of course, highlight the need to vaccinate people who previously had COVID-19. Immunity Michlmayr, a researcher in the Bacterial, Parasite and Fungal Division of Staten Serums Institut in Copenhagen, Denmark, said:

Population-based observational studies Published online March 17 Lancet..

“This finding makes sense because patients with immunodeficiency and older patients may not have a long-lasting immune response,” Dr. David Hirschwerk was asked to respond to the findings of the study. I told Medscape when I was there. “Even if previously infected with COVID, it emphasizes the importance of vaccination for older people.

“For those who were infected last spring and have not yet been vaccinated, this helps support the value of pursuing yet. vaccine“Hirschwerk, an infectious disease specialist at Northwell Health in Manhasset, NY, 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 tests returned positive for SARS-CoV-2 during the first surge in Denmark between March and May 2020. I found that. Positive during 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.

“My overall view is that it’s great to be able to see this question on such a large dataset,” E. Dr. John Welly told Medscape. The findings support “what we saw in previous small studies.”

Natural protection against about 80% reinfection, vaccineBut it’s not bad, “added Welly, director of the Institute of Immunology, University of Pennsylvania, Philadelphia.

Does age change immunity?

“Our finding that older people are more likely to be positive again if they are already tested positive than younger people can be explained by the natural changes that accompany age. Immune system Of the elderly, also known as immune aging, “the authors say.

The researchers found no significant difference in reinfection rates between women and men.

Similar to previous studies, this study also shows that the first seizure of COVID-19 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, SARS-CoV-2 reinfection Data that clearly show the risk already exists, despite previous infections with the original strain of the virus. “

The emergence of variants of concern that could escape innate and vaccine-related immunity “complexes the problem,” said Rosemary J. Boyton (MBBS) and Daniel M. Altman (PhD) of Imperial College London. Wrote as follows. 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.”

Vaccines appear to have better protection against recurrent infections, measured in terms of neutralizing antibodies and T cells, compared to previous infections, Boyton and Altman write. ..

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.