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Study: COVID-19 Booster Shots Elicit Longer Immunity than Primary Series Alone


Researchers found that the COVID-19 booster dose elicited a 71%-84% increase in the median anti-spike half-life over that of the primary series.



Immunity after a COVID-19 booster shot lasts longer than from the primary series alone, according to new research published in the journal Scientific Reports.1

In a study analyzing anti-spike IgG waning kinetics in persons who received an mRNA-based primary series (first 2 doses) and a subset of individuals who then received an mRNA-based booster dose, researchers found that the booster dose elicited a 71%-84% increase in the median anti-spike (Anti-S) half-life over that of the primary series.1

“It was really interesting to see the SARS-CoV-2 booster dose have such a huge increase in protective longevity capacity as compared to the primary series of two doses,” said lead author Chapin Korosec, PhD, Modelling Infection and Immunity Lab, Mathematics and Statistics, York University, Ontario, Canada, in a university press release.2

To date, there have been hundreds of millions of COVID-19 vaccine booster doses administered worldwide. It is well-known that vaccine waning kinetics are impacted by the presence of various comorbidities, age, and prior infection, therefore, “it is critical to understand how dose-dependent immunity from vaccination wanes amongst those at increased risk of severe illness from COVID-19 in order to optimize continuity of care,” wrote Korosec and colleagues.1

Researchers used health data submitted to the COVID Immunity Task-Force project to analyze individual-level immune decay profiles of reported spike-specific humoral immune data for 152 individuals who received an mRNA-based primary series and a subset of 137 individuals who received a booster dose. Of particular interest to Korosec and colleagues was how decay rates after each series scale as a function of participant age and whether there is any influence of sex or of the presence of multiple chronic noncommunicable diseases on the decay profile.1


Investigators found that the median Anti-S half-life was 63.3 days (interquartile range [IQR] 7.9 days) for the primary series and increased to 115 days (IQR 20 days) for those who received an mRNA booster dose. “Therefore, taking the IQR range into account, the booster dose exhibits a 71–84% increase in Anti-S half-life over that of the primary series,” they wrote.1

Results also showed that the Anti-S half life for both the primary series and booster doses decreased with age. A linear fit of the individual decay rates with age demonstrated that half-life decreased by 0.1 days per year of age for the primary series and 0.13 days per year of age after the booster dose, according to the study.1

When they analyzed the association of sex at birth with decay rate, the investigators’ single-variate statistical test found no significant difference in the kinetics of decay between men and women. However, in multivariate analysis there was a statistically significant, albeit small, bias in favor of men.1

The researchers also analyzed decay rates as a function of the number of self-reported chronic comorbidities. They found the Anti-S decay rate increased with up to 4 comorbidities and then, in participants with 5 chronic conditions, the rate decreased relative to those with 4 comorbidities. In this vein they reported that the variable with the strongest power to explain humoral decay after both primary series and booster dose was the presence of chronic lung disease. However, individuals with pre-existing asthma had a stronger primary series humoral response to vaccination compared to those that did not. This result was sustained for the booster dose, added investigators.1

“…Although chronological age continues to be a good proxy for vaccine-induced humoral waning, imunosenescence is likely not the mechanism, rather, more likely the mechanism is related to the presence of noncommunicable diseases, which also accumulate with age, that affect immune regulation,” Korosec and colleagues noted in conclusion.1


  1. Korosec CS, Dick DW, Moyles IR, Watmough J. SARS-CoV-2 booster vaccine dose significantly extends humoral immune response half-life beyond the primary series. Sci Rep. 2024;14:8426. doi:10.1038/s41598-024-58811-3
  2. COVID-19 booster immunity lasts much longer than primary series alone, York-led study shows. News release. York University. April 18, 2024. Accessed April 22, 2024. https://www.yorku.ca/news/2024/04/18/covid-19-booster-immunity-lasts-much-longer-than-primary-series-alone-york-led-study-shows/

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