In addition to guarding against current strains of SARS-CoV-2, COVID-19 vaccine boosters may also help protect against some future coronaviruses that have spillover potential.
For the study, published in npj Vaccines, researchers tested blood samples from older UK adults (average age around 69) who had received four COVID-19 vaccine doses, including a bivalent booster covering both the original Wuhan strain and the Omicron variant.
They tested how well antibodies in these blood samples could neutralize different Omicron variants of SARS‑CoV‑2. They also tested the antibodies to see if they could neutralize the SARS‑CoV‑1 virus—responsible for the 2003 SARS outbreak—and a range of closely related coronaviruses (known as sarbecoviruses) found in bats and pangolins.
As expected, antibodies performed worse against newer Omicron variants than the original Wuhan strain, showing how the virus has evolved to escape the immune response. The antibodies were also poor at neutralizing SARS‑CoV‑1, which is genetically more distant.
Surprisingly, though, they were much better at neutralizing two sarbecoviruses closely related to SARS‑CoV‑2—one from bats and one from pangolins—than they were at neutralizing the original Wuhan strain itself, even though these two viruses have never infected humans.
The researchers link this cross-protection to “immune imprinting,” a related phenomenon they explored in a second study published in iScience. This occurs when a person's first exposure to SARS-CoV-2—through infection or vaccination—shapes how their immune system responds to future variants for years afterward. Because the original vaccine trained antibodies against the Wuhan strain, and some animal coronaviruses have spike proteins more similar to that original strain than to Omicron, that early imprint may be inadvertently offering broader protection.
Researchers say the findings could shape next-generation vaccine design, particularly vaccines targeting spike protein regions shared across multiple coronaviruses as new spillover threats emerge from animal populations.
Data from University of Cambridge