A primary dose of TCV is safe and provides clinical efficacy up to two years of follow-up in all children and a sustained immunity in older children three to five years after immunization, noted researchers from the Oxford Vaccine Group and the icddr,b. But on the other hand, it presents a relative decrease in the exhibited immunization at later time points in the children who were vaccinated earlier.
TyVOID population based study conducted by Rappaport et al by providing consent L137 in The Lancet identified a number of cases of TCV in Bangladeshi children over five years and proved the higher vaccine efficacy (80 – 96%) within two years of vaccination among all children of Bangladesh.
The paper is titled “5-year vaccine protection following a single dose of Vi-tetanus toxoid conjugate vaccine in Bangladeshi children (TyVOID): a cluster randomised trial.
In children who had received the TCV in 2018/2019 and 2021, the incidence of typhoid three to five years after vaccination was three fold higher, indicating waning effectiveness, particularly among the very young.
The data indicated that children who received the first dose at or after two years of age retained good protection (59 to 85%) at 3 to 5 years after vaccination.
Thus, TCV provides the only realistic opportunity to lessen the toll of typhoid illness and limit the further development of drug-resistant subpopulation. Carrying out this research offers policy makers a further understanding and longer-term TCV protection accompanied by future research on the topic and up to date guidelines.
Dr. Firdausi Qadri, the Senior Scientist, Infectious Diseases Division, icddr, b, Bangladesh, and the first author of the paper, said this writing is built on the audience of TyVOID, a progression of the TyVAC cluster randomised controlled trial unmasked in 2021, and followed up until the midpoint of 2023.
‘The results presented here suggest declining levels of immunity in the various age cohorts and hint at the possibility of a booster dose at around school going age of children who were vaccinated before 2 years of age to maintain protection from TCV in school going age when children were at highest risk for typhoid’.
This is according to the World Health Organization which advises that for infants and children between 6 months of age, a single dose of TCV only is sufficient.
The first typhoid conjugate vaccine (TCV; Bharat Biotech International) was approved by WHO in 2017 and in 2018 WHO listed vaccines as an essential tool in the prevention and control of typhoid fever. As for the year 2025, TCV will be incorporated in vaccination events in children throughout Bangladesh.
This report supports the requirement to conduct more research on the typhoid burden after TCV implementation and more data regarding the duration of additional vaccine protection from real-life high-incidence settings, as well as for insight into trends in antibiotic resistance to inform the WHO’s position.
Reference:
Oxford U of. Typhoid vaccine trial confirms sustained protection for older children Medical Xpress
