One year into the COVID-19 pandemic, researchers have gained valuable insights into the duration of natural immunity from infection. A rigorous U.S. study, published in Science, reveals this immunity persists for at least 8 months. What does this mean for protection?
Earlier research painted a mixed picture: a December 2020 UK study found antibodies against the coronavirus waned in weeks, with 25% of people losing them within three months. A prior U.S. preprint suggested at least 6 months of immunity, but required validation.
Now, experts at the La Jolla Institute of Immunology (U.S.) provide stronger evidence in a peer-reviewed study from January 6, 2021, in Science. They tracked immune memory in 188 COVID-19 patients (80 men, 108 women) across asymptomatic, moderate, and severe cases, monitoring responses more than 8 months post-symptoms.
Immune memory forms after the initial encounter with a pathogen, whether natural or via vaccine. It involves neutralizing antibodies that target invaders immediately and memory cells that mount a swifter, stronger defense upon re-exposure.
The team measured circulating anti-SARS-CoV-2 antibodies, which varied across participants but remained stable from 20 to 240 days post-symptoms. After one month, 98% of patients tested positive for anti-spike protein antibodies. By 6 months, levels had declined but persisted in 90%, with a half-life of about 103 days. Neutralizing antibodies endured beyond 6 months, present in 90% of patients at 6-8 months.
Memory cells followed: B cells, CD8+ T cells, and CD4+ T cells specific to the virus emerged around one month post-symptoms. At 6 months, 70% retained CD8+ T cells (half-life 125 days) and 92% had CD4+ T cells (half-life 94 days). B cells appeared later (4-5 months) and showed signs of long-term persistence.
Reinfectious cases despite this? The study highlights variability in immune responses—weaker ones may not fully protect against the virus.
