U-M study: Natural COVID infections provide protection against reinfection, two variants

Vaccines still provide far more protection, according to CDC

FILE - This 2020 electron microscope image provided by the National Institute of Allergy and Infectious Diseases - Rocky Mountain Laboratories shows SARS-CoV-2 virus particles which cause COVID-19, isolated from a patient in the U.S., emerging from the surface of cells cultured in a lab. Viruses are constantly mutating, with coronavirus variants circulating around the globe. (NIAID-RML via AP) (Uncredited)

ANN ARBOR – Natural COVID-19 infections helped protect from reinfection when the delta and gamma variants were prevalent during the pandemic, according to new research by the University of Michigan.

For the study, researchers examined cases in a community setting in Nicaragua and found that antibodies acquired through natural infection provided individuals with 69% protection against reinfection. Those same antibodies also provided 79% protection against illnesses becoming moderate or severe. Researchers also found that second infections were less severe -- though not as much as researchers had hoped -- than initial infections.

“The course of the pandemic will be determined by the quality and durability of the protective immunity offered by both natural infection and vaccination,” Hannah Maier, a postdoctoral research fellow at U-M’s School of Public Health and lead author of the report, said in a release. “We hope having an immune correlate of infection-induced protection and a better understanding of the severity of second infections will inform vaccine policy and help guide targeting at-risk populations and other mitigation strategies.”

Despite the study’s findings, vaccines continue to provide the most protection against both infection and severity of illness caused by COVID-19. According to the Centers for Disease Control and Prevention, the Pfizer-BioNTech vaccine was 95% effective at preventing infection during clinical trials. Similarly, Moderna’s vaccine was 94.1% effective at preventing infection during clinical trials in people aged 18 years or older.

The study, which is now under peer review, used the ongoing Household Influenza Cohort Study in the Nicaraguan city of Managua. The study was launched in 2017 before the COVID-19 pandemic began and initially studied influenza in households. In February 2020, the study expanded to include SARS-CoV-2 cases.

According to a U-M release, participants who take part in the study are instructed to report to a health center at the onset of any illness. Participants also provide blood samples for serology each year during March and April, an an additional sample was collected in October 2020 from those who consented.

A sub-study within the study analyzes transmission within households of SARS-CoV-2 once a family member tests positive.

Prior to a large second wave of coronavirus cases in March 2021, researchers discovered that 62% of the cohort’s participants were seropositive for COVID-19 and that the delta and gamma variants were the dominant strains.

From these samples, the researchers were able to determine antibody levels required to fight infection, illness and severity of symptoms.

Senior author of the paper Aubree Gordon said that ultimately vaccination against COVID-19 would ease the burden of the pandemic on the community, and that vaccines are still difficult to get in low- and middle-income countries.

“The emergence of variants is really stressing that vaccine equity is incredibly important. We’re all in this world, in this boat together and we really need to make sure the vaccines get out to low and middle income countries,” she said in a release. “With Omicron, there’s a lot that we don’t know. We anticipate that protection would be lower than what we saw for this study.”

According to a U-M release, other authors of the study include: John Kubale, a research fellow at U-M’s School of Public Health; Angel Balmaseda, Sergio Ojeda, Nery Sanchez, Miguel Plazaola, Roger Lopez, Saira Saborio, Carlos Barilla and Guillermina Kuan, all with the Sustainable Sciences Institute, Managua, Nicaragua; and Eva Harris and Harm van Bakel, Mount Sinai, School of Public Health, University of California, Berkeley.

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