Prior Infection Found to Be Significantly Protective Against COVID-19

Prior infection provided considerable protection against severe COVID-19, especially with the Delta variant but also with the Omicron variant until antibody response declined rapidly. The problem, however, is that the situation could be totally different with the appearance of new SARS-CoV-2 variants, the authors caution. Here are more details.

PORTLAND, OR – The good news in a recent Living, Rapid Review is that a sustained antibody response to SARS-CoV-2 infection was found to be considerable for both Delta and Omicron variants and that prior infection protected against reinfection with both variants, although the protection was weaker for Omicron and declined rapidly.

The bad news, according to the report in Annals of Internal Medicine, is that the information is likely to have little clinical applicability as new variants emerge.

The durability of the antibody response after SARS-CoV-2 infection and the role of antibodies in protection against reinfection remain unclear, however.

Researchers from the Scientific Resource Center for the Agency for Healthcare Research and Quality in Portland, OR, and colleagues sought to synthesize evidence on the SARS-CoV-2 antibody response and reinfection risk, while also identifying gaps from prior reports.

To do that, they searched MEDLINE (Ovid), EMBASE, CINAHL, the World Health Organization Research Database, and reference lists from Dec. 16, 2021, through July 8, 2022, with surveillance through Aug. 22, 2022. Included were English-language cohort studies evaluating IgG antibody duration at least 12 months after SARS-CoV-2 infection, the antibody response among immunocompromised adults, predictors of nonseroconversion, and reinfection risk. Study data was sequentially extracted by two investigators who rated the quality.

Results indicated that most adults had IgG antibodies after SARS-CoV-2 infection for longer than 12 months, although that was rated as low strength of evidence [SoE]). While most immunocompromised adults developed antibodies, they did not do so at as high a rate as immunocompetent adults (moderate SoE for organ transplant patients and low SoE for patients with cancer or HIV).

“Prior infection provided substantial, sustained protection against symptomatic reinfection with the Delta variant (high SoE) and reduced the risk for severe disease due to Omicron variants (moderate SoE),” the authors note. “Prior infection was less protective against reinfection with Omicron overall (moderate SoE), but protection from earlier variants waned rapidly (low SoE).”

Researchers state that their study was limited by being a single review for abstract screening and a sequential review for study selection, data abstraction, and quality assessment.

“In March 2021, we published the first version of a rapid, evolving, pragmatic review that described the antibody response in adults after an infection with SARS-CoV-2. In January 2022, we published a second review, meta-analysis, and data visualization describing the risk for SARS-CoV-2 reinfection,” the authors recount. “Our objectives in conducting the original review were to assess the prevalence, level, and duration of the antibody response after infection; compare the risk for reinfection among those with a prior infection to persons who had never been infected; and examine the duration of protection against reinfection.”

The study found that before the emergence of the Delta and Omicron variants, prior infection with the wild-type SARS-CoV-2 virus or the Alpha variant reduced the risk for reinfection by 80% to 97% (pooled estimate, 87% [95% CI, 84% to 90%]) compared with those who had not been protected.

After a median follow-up of 8 months, protection remained above 80% for at least 7 months, according to the researchers, who add, “There was sparse evidence on the duration of detectable antibodies beyond 6 months; whether the antibody response varied based on immunocompromised status or other factors, such as asymptomatic infection; and whether testing for SARS-CoV-2 antibodies provided clinically useful information about reinfection risk (that is, whether detectable antibodies correlated with protection).”

Evidence gaps identified in the previous 2 versions were addressed in this version, with a focus on “the persistence of IgG antibodies for longer than 12 months after infection, whether the antibody response varies in immunocompromised persons, and characteristics of those who do not seroconvert (key question [KQ] 1),” according to the authors. “We also evaluated available evidence regarding reinfection with Delta or Omicron variants after previous infection and the relation of antibody levels, symptoms status, and age to protection against reinfection (KQ2) as well as the duration of protection in the context of Delta and Omicron variants (KQ3).”

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