BCG Vaccine Immunity Against Tuberculosis More Lasting Than Earlier Believed

BCG Vaccine Immunity Against Tuberculosis More Lasting Than Earlier Believed

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Highlights:
  • The Bacillus Calmette-Guerin (BCG) vaccine is given in several countries during infancy to protect from tuberculosis (TB) infection but the duration of its effect remains unclear
  • Current study suggests that BCG vaccine protects nearly twice as longer than previously thought
  • Early vaccination is therefore essential to prevent tuberculosis in adulthood when disease transmission is maximum
Protective effect of BCG vaccine against tuberculosis may last much longer than currently believed, according to a recent study at the London School of Hygiene & Tropical Medicine (LSHTM) and funded by the National Institute for Health Research.
BCG Vaccine Immunity Against Tuberculosis More Lasting Than Earlier Believed

Duration Of BCG Vaccine Protective Effect In Tuberculosis Prevention - Aim Of Current Study
Although BCG vaccine is widely administered in several countries, the duration of its protective effect remains unclear, an issue the current study aimed to address.

It is widely believed that BCG immunity lasts for upto 15 years but published research from Brazil and Norway have indicated that the duration of immunity might be longer. Environmental and genetic factors also may play a role.

Dr Punam Mangtani, the lead author of this study remarked "Previous studies have shown BCG can offer good protection against TB for up to 10-15 years following vaccination of secondary schoolchildren, but we do not know the duration of protection in different populations.

The current case control study was undertaken in Britain at the London School of Hygiene and Tropical Medicine. The results of the study appear in the journal International Journal of Epidemiology of August 2017.

Details and Findings Of The Study

  • The case control study covered 677 cases diagnosed with TB and 1170 controls without a previous history of the disease. The two groups were matched on year of birth and the team controlled for social and demographic variables including living region, drug use and education.
  • The participants had been given BCG vaccine between 12-13 years of age and the study assessed the level of protection 10-29 years later when they were adults and transmission of disease is the highest.
  • Adults in both groups were queried about their vaccination history by specially trained interviewers and inspected for BCG vaccination scars.
The notable findings from the study were the following
  • Overall, 75% of cases were vaccinated compared to 86% of controls.
  • TB was 50 percent less likely to occur in vaccinated children compared with unvaccinated children 10 to 20 years later.
  • The protective effect of BCG then waned after 20 years.
The findings of the study seem to confirm other published reports that the efficacy of the BCG vaccine might have been underestimated all these years and actually lasts twice as longer than previously believed.

Major Takeaways From The Study

The following are the most important lessons from the study findings.
  • With no new vaccine against TB, the BCG vaccine continues to be important in preventing disease spread, particularly in areas where TB risk is high but vaccination coverage remains low, such as parts of Central and Western Africa, East Asia and the Pacific.
According to Dr Mangtani, "Tuberculosis kills nearly two million people every year, more than HIV/AIDS, but TB prevention methods have changed little in half a century. Progress in developing new TB vaccines is slow with BCG, developed in the 1920s, still the only option."
  • The fact that BCG vaccine offers protection for longer than originally assumed would be reassuring for persons who have had the vaccination as children.
  • The findings provide a yardstick against which the efficacy of any emerging TB vaccines could be measured. There are at least 10 under development currently, but failed to show any protection in trials.
  • The findings lend support to voices in favor of BCG vaccine and the continuing efforts of the World Health Organization (WHO) to control TB.
  • More funds and resources need to be allocated to ensure that BCG vaccination has a wider reach worldwide. The study could serve to boost BCG programs in areas where it is slack.
In the words of Dr Mangtani, "BCG is not perfect but until a new, more effective vaccine is approved and rolled-out, we should be maximising its potential. We should also be supporting the various agencies that make sure BCG is readily available globally."

Tuberculosis Infection and BCG Vaccination - Facts and Figures

  • Tuberculosis (TB) infection, caused by Mycobacterium tuberculosis, mainly involving the lungs is a leading cause of mortality and morbidity in certain parts of the world.
  • Two to three billion of the world's population is affected, and it is estimated that 10% progress to clinical disease.
  • In 2015 there were an estimated 10.4 million new cases of TB and 1.8 million deaths worldwide.
  • Six countries contributed to nearly 60% of the new cases namely India, Indonesia, China, Nigeria, Pakistan and South Africa.
  • In addition to TB Patients living with human immunodeficiency virus (HIV), Multi Drug Resistant TB (MDR-TB) has added a new dimension to this scourge.
  • The Bacillus Calmette-Guérin (BCG) vaccination, named after the French scientists who developed it, was first used in 1921.
  • Despite the passage of time and the limited protection it offers, there is still no other vaccine although many have undergone trials.
  • It is a live attenuated (weakened) vaccine administered by intradermal injection. It should not be given to persons with a weak or reduced immunity.
In conclusion, the study reiterates the importance of BCG vaccine in prevention of tuberculosis and spurs policy makers and fund allocators to take a relook at their immunization policies.

References:
  1. Punam Mangtani, Patrick Nguipdop-Djomo, Ruth H Keogh, Jonathan AC Sterne, Ibrahim Abubakar, Peter G Smith, Paul EM Fine, Emilia Vynnycky, John M Watson, David Elliman Marc Lipman, Laura C Rodrigues. The duration of protection of school-aged BCG vaccination in England: a population -based case-control study. International Journal of Epidemiology,(2017) DOI:https:doi.org/10.1093/ije/dyx141
Source: Medindia

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