Nothing lasts forever, including baby BCG vaccine protection

Babies born with the bacille Calmette-Guérin vaccine are protected against tuberculosis in early childhood, but this protection largely disappears within a few years, according to a meta-analysis.

BCG was 18% effective against TB vaccination in all age groups. However, when the results were stratified by age, infant vaccination showed a significant effect only in children younger than 5 years old, said Dr. Leonardo Martinez of Boston University and colleagues at The Lancet Global Health. Reported .

Subgroup analyses that stratified data according to tuberculin skin test and IFNγ release test results and tuberculosis type also showed that efficacy increased with Declining trend with age: When children reach puberty, the effect of infant vaccination is still evident. (However, findings from subgroups have very wide 95% confidence intervals, making it difficult to draw firm conclusions.)

Overall, the analysis suggests that children are at risk for: Booster doses may be necessary for TB to get older.

“[T]There is widespread debate about the effectiveness and duration of protection of BCG, and whether the vaccine is only effective in selective settings,” Martinez told Today’s medical page . “Our findings show that BCG vaccination is effective in preventing TB in young children. Because childhood TB can be a very serious and debilitating disease in infants, it is important to continue BCG vaccination.”

“However, since the results show that the vaccine is not effective in adolescents and adults, stronger immune protection is needed in the elderly population,” Martinez continued. “We urgently need new vaccines to complement BCG vaccines in high TB ​​burden areas.”

This meta-analysis draws on a case cohort study of TB contacts published in January 1998 2018 April. Participant-level data were obtained from 26 cohort studies in 17 countries with a total of 68,552 participants. In order to be included, an article’s dataset needed to have a follow-up period of at least six months, information on the age and sex of the individual’s TB contacts, and dates of study start and follow-up.

Studies were excluded if no information on BCG vaccination was provided, or if studies were conducted in countries where BCG vaccination at birth is not recommended (not recommended in the United States). Individual-level participant data took into account a range of variables, including characteristics of exposed participants (contacts), index cases, and setting.

Exposures were defined as close contacts (whether living in the same household with a person with a microbiological or radiological diagnosis of TB or substantial interaction outside the household. Baseline assessment) and events (New TB cases diagnosed more than 90 days after baseline) TB cases. Secondary outcomes considered incidence and mortality of pulmonary and extrapulmonary tuberculosis.

Data adjusted for variable of interest, baseline age, sex, previous TB, and data collected prospectively or retrospectively. Results are by age of exposure and Mycobacterium tuberculosis infection status was stratified.

Martinez and colleagues expressed vaccine efficacy as the odds ratio for infection, comparing vaccinated and exposed individuals to unvaccinated individuals. In many analyses, the odds ratio for people aged 10 and older was close to 1, and often greater than 1. But in no case was there a statistically significant result that BCG increased the risk of contracting TB.

For mortality only, infant vaccination provided significant protection during adolescence, with an adjusted odds ratio of 0.13 (95% CI 0.04-0.41) at 10-14 years, which was comparable to the younger age group efficacy is similar. But for those 15 and older, there was no apparent benefit at all (aOR 1.13, 0.35-3.68).

The studies used in this meta-analysis were observational in nature and, therefore, were not randomized. Despite the adjustment, there may still be residual or unmeasured confounding variables. BCG vaccines are classified by vaccine scarring, which may lead to misclassification if no scarring occurs. In addition, mortality analyses must be carefully interpreted because vaccinated children may be from higher socioeconomic status and may have better access to health care. Finally, extrapulmonary TB is often underestimated.

“The BCG vaccine was originally invented more than 100 years ago,” Martinez told Medicine Today Page . “Our The findings suggest that it lacks efficacy in general and is only really effective in young children under the age of 5. Although more than 10 million people develop tuberculosis and kill more than 1 million each year, a new vaccine is not yet available .”

“We urgently need new research into novel vaccines that can prevent the development of TB — especially in adolescents and adults,” Martinez added. “Several novel vaccines have shown some promise, but more funding and work is needed in this area.”

James Lopilato is a staff writer for Medpage Today. He covers a variety of topics currently being explored in medical scientific research.

Disclosure

This study was funded by the National Institutes of Health.

Martinez reports no conflict of interest.