While COVID-19 is no longer the global crisis it once was, the virus continues to circulate and evolve, prompting ongoing research into the duration of vaccine protection. A new study from the University of Antioquia in Colombia reveals that antibody levels generated by vaccination decrease significantly within six to twelve months, raising questions about long-term immunity and the need for continued vigilance.the research, focused on nearly 2,000 vaccinated individuals, underscores the importance of understanding how waning immunity impacts public health strategies, particularly for vulnerable populations like seniors and those with pre-existing conditions.
Five years after the emergence of SARS-CoV-2, the virus that causes COVID-19, the pandemic no longer dominates daily life. Daily case counts and widespread lockdowns are a thing of the past, but the virus continues to circulate, and evidence suggests that the protection offered by vaccines is waning over time.
This is according to a new study from researchers at the University of Antioquia, in collaboration with the Departmental Public Health Laboratory of the Antioquia Governorate, which investigated how long vaccine-induced immunity actually lasts. Understanding the duration of vaccine protection is crucial for informing public health strategies and protecting vulnerable populations.
The research found that antibody levels decrease significantly between six and 12 months after completing the initial vaccination series, though this decline is gradual.
“The loss of vaccine immunity has been particularly studied since the emergence of the Omicron variant and its subvariants,” explained Doracelly Hincapié Palacio, a doctor in epidemiology and faculty member at the National School of Public Health.
The Omicron variant, which emerged in late 2021, marked a turning point as reinfections increased and it became clear that protection wasn’t indefinite.
Although the pandemic appears to be receding, national epidemiological data demonstrates why the question of immunity duration remains relevant. According to the latest national epidemiological bulletin from the National Institute of Health, as of November 1, 2025, Colombia had reported 7,093 cases of COVID-19 this year and 120 deaths associated with the disease, the majority occurring in individuals aged 60 years or older.
Epidemiologists Viviana Lenis Ballesteros and Carlos Arango Úsuga, members of the research team, believe the current behavior of the virus aligns with that of an endemic disease, characterized by persistent circulation, seasonal peaks, and localized outbreaks in vulnerable populations.
Antioquia exhibits a similar pattern, with a consistently low but present epidemic risk, influenced by the emergence of new variants and the gradual reduction in immune protection.
The study, titled Serovigilance of anti-SARS-CoV-2 IgG antibodies in at-risk groups in Antioquia (2022–2023), measured the persistence of IgG antibodies, which reflect immunological memory.
A total of 1,958 vaccinated individuals from 11 municipalities in the department, including Medellín, participated in the study. The group included residents of long-term care facilities, healthcare workers, and members of the university community.
Detailed analysis was conducted on 561 individuals with longitudinal follow-up for more than a year. “We found that, although 99.8% of participants had antibodies after completing the vaccination schedule, these levels decreased significantly between six and twelve months,” explained Marta Ospina and Seti Buitrago Giraldo, researchers at the Antioquia Departmental Public Health Laboratory.
This reduction in antibodies was more pronounced in individuals over 60 years of age and those with underlying health conditions.
However, this finding has important nuances. A decrease in antibodies doesn’t equate to a complete loss of protection. “Other mechanisms, such as cellular immunity, can remain more stable over time,” clarified Héctor García, a faculty member and researcher at the University of Antioquia’s Faculty of Medicine.
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Long-term immunological memory was not measured in the study due to technical demands and costs, but it plays a key role in preventing severe illness.
Why is the coronavirus still circulating?
Pablo Patiño Grajales, dean of the University of Antioquia’s Faculty of Medicine and a master’s in immunology, explains that the continued circulation of COVID-19 in the country is due to mutations of SARS-CoV-2, heterogeneous vaccine coverage, reduced epidemiological surveillance, and the gradual loss of natural and vaccine-induced protection over time.
Colombia currently has updated Pfizer-BioNTech and Moderna vaccines available, prioritized for individuals over 60, those with comorbidities, healthcare personnel, and pregnant individuals.
“Vaccines work and are safe, but their protection is not permanent. It is necessary to maintain complete vaccination schedules and boosters,” concluded the dean.
