COVID-19 vaccination and utility of booster dose: A community-based cross-sectional study

In 2023, the WHO declared the end of the COVID-19 pandemic, cautioning that the virus will continue to mutate and may cause sporadic outbreaks. Vaccination was critical in controlling the pandemic, though concerns persist about long-term immunity and the need for booster doses. The study aimed to assess whether vaccination enhances immunity beyond natural infection and determine the ongoing need for booster doses.

This population-based cross-sectional study was conducted across ten districts in Uttar Pradesh, India, to evaluate humoral and cellular immune responses in vaccinated individuals (ChAdOx1nCoV-19 vaccine & BBV152) or those previously infected with SARS-CoV-2. Six hundred forty-three participants were assessed for cellular immunity and 7000 for humoral immunity. Anti-receptor binding domain (RBD) antibodies were measured using enzyme-linked immunoassay (ELISA), and various subsets of memory T-cells were analyzed via flow cytometry.

The study revealed that vaccination significantly elevated antibody titers compared to natural infection (p < 0.001), with the most significant increase observed after the second dose (p < 0.001). While subsequent doses raised antibody levels, the increase between the second and third doses was modest. T-cell responses, particularly memory subsets such as effector memory (p = 0.009), central memory (p = 0.003), and stem cell memory (p < 0.001), showed significant enhancement after the second dose but plateaued following the third dose, suggesting further doses may not be beneficial.

While vaccination effectively increases antibody levels and reduces hospitalizations and severe outcomes, additional booster doses may offer limited benefits for the general population, as there appears to be a ceiling effect in both humoral and cellular immunity after the second dose. Given the potential adverse effects of COVID-19 vaccination, the decision to administer multiple booster doses to specific population groups must be based on further studies that directly address this issue, along with a thorough risk-benefit analysis.