WHO TAG-CO-VAC: Monitoring SARS-CoV-2 Variants and Vaccine Efficacy

Recommendations for Monovalent JN.1 Lineage Vaccines Highlighted; Gaps in Surveillance and Data Emphasized.

The World Health Organization's Technical Advisory Group on COVID-19 Vaccine Composition (TAG-CO-VAC) has released its latest findings and recommendations following a review of SARS-CoV-2 variant evolution, immune responses, and vaccine performance. Meeting from December 10–12, 2024, TAG-CO-VAC emphasized the importance of ongoing surveillance and vaccine updates to combat the ever-evolving landscape of COVID-19.

TAG-CO-VAC highlighted the continued global circulation of SARS-CoV-2, with JN.1-derived lineages dominating the genetic landscape. Variants such as KP.3.1.1, XEC, and other descendent lineages have shown antigenic similarities to JN.1, supporting the use of monovalent JN.1 lineage vaccines.

Key findings included:

Antibody Responses: Vaccination with monovalent JN.1 or KP.2 formulations demonstrated robust neutralizing antibody titers against circulating variants, with a modest 2-fold reduction for some descendent variants such as KP.3.1.1 and XEC.

Comparative Efficacy: While monovalent XBB.1.5 vaccines provided some protection during JN.1 circulation, JN.1-based vaccines exhibited broader efficacy against descendent variants.

Neutralizing Titers: Clinical and preclinical data show consistent cross-reactivity among JN.1-derived variants, affirming the antigenic closeness of KP.2, KP.3.1.1, and XEC to the original JN.1 strain.

Recommendations for Vaccine Composition

TAG-CO-VAC recommended maintaining the current monovalent JN.1 lineage vaccine antigen composition as an effective approach to enhance immune responses against JN.1 and its variants. However, alternative formulations demonstrating broader efficacy may also be considered.

The group also emphasized the WHO’s stance that vaccination programs should not delay administering currently available vaccines while awaiting updated formulations.

Limitations and Data Gaps

Despite advancements, TAG-CO-VAC identified critical gaps in the evidence base:

Surveillance Deficiencies: Persistent underreporting of cases, hospitalizations, and deaths, alongside limited genomic surveillance, hinders the ability to monitor variant evolution effectively.

Diverse Immune Responses: Limited data on cellular immunity and neutralizing antibody titers against recent variants restrict comprehensive understanding.

Global Vaccine Efficacy (VE): A paucity of geographically diverse VE studies reduces confidence in extrapolating findings to varied populations.

TAG-CO-VAC strongly advocates for strengthened epidemiological and virological surveillance and clinical evaluation of new vaccine formulations.

Future Directions

Moving forward, the group seeks data on:

Immune responses across diverse populations to JN.1-based and other vaccines.

Clinical outcomes, including VE against emerging variants.

Comprehensive evaluation of new variant-specific vaccine antigens.

The WHO TAG-CO-VAC reaffirmed its commitment to reassess COVID-19 vaccine antigen composition every six months. Their work underscores the importance of adaptive vaccine strategies and robust global surveillance to mitigate the ongoing impact of SARS-CoV-2.

For more details on TAG-CO-VAC's findings and recommendations, visit the WHO website.