Long-Term Effects of Multiple Updated Vaccinations Against SARS-CoV-2 Revealed in New Study

Strategic Insights -

New research published in the Infectious Disease Reports journal has investigated the long-term effects of multiple updated vaccinations against SARS-CoV-2. The study, conducted by researchers from the Yokohama City University Hospital in Japan, analyzed the humoral and cellular immunity dynamics in healthcare workers who received 3-7 vaccine doses over a four-year period.

Key Takeaways:

  • The study enrolled 32 healthcare workers (median age, 47 years) who received 3-7 vaccine doses, with blood samples collected at five time points from April 2021 to January 2024.
  • The neutralizing titer (NT50) against the original Omicron XBB and Omicron BA.2.86 strains was detected before the Omicron vaccine was introduced and increased following the updated vaccination.
  • The NT50 against the Omicron XBB and BA.2.86 strains was elevated after natural infection by the Omicron strain, albeit without differences compared with the findings in uninfected subjects.
  • Multivariate regression analysis revealed no confounder that affected the antibody titer against the BA.2.86 strain at the fifth blood sampling.
  • The median number of spot-forming cells (SFCs) ranged from 78 to 208 after the first two doses.
  • The study concluded that multiple vaccinations induced the production of antibodies with divergent activity against emerging mutant strains and enhanced protective effects against the original strain.

Statistics:

  • 32 healthcare workers (median age, 47 years) were enrolled in the study.
  • 3-7 vaccine doses were administered to the participants.
  • Blood samples were collected at five time points from April 2021 to January 2024.
  • The neutralizing titer (NT50) against the Omicron XBB and Ba.2.86 strains was detected in 27-31 participants.

Sources:

  • NewsRx. New COVID-19 Research from Yokohama City University Hospital Discussed (Humoral and Cell-Mediated Immunity Against SARS-CoV-2 in Healthcare Personnel Who Received Multiple mRNA Vaccines: A 4-Year Observational Study). Medical Letter on the CDC & FDA. July 13, 2025; p 158.
  • Infectious Disease Reports. Humoral and Cell-Mediated Immunity Against SARS-CoV-2 in Healthcare Personnel Who Received Multiple mRNA Vaccines: A 4-Year Observational Study. 2025, 17(3):42. (MDPI AG)
  • Journal article available at: https://doi-org.sdpl.idm.oclc.org/10.3390/idr17030042.