Previously thought to be effective for 10-15 years, a new case-control study found that if given in early teenage years (12-13), the Bacillus Calmette-Guérin (BCG) vaccine protected over 50% of UK children against TB for at least 20 years, then waned. The research was led by the London School of Hygiene & Tropical Medicine and funded by the National Institute for Health Research. Although some studies in countries such as Brazil and Norway have indicated that BCG might be effective for longer than first thought, this study provides the most robust evidence to date.
With no new vaccine for TB imminently available, the researchers say their findings highlight the important role BCG is playing in preventing the spread of the disease, and provide an argument for uptake to be higher in areas where TB risk is high but vaccination coverage is low, such as parts of Central and Western Africa, East Asia and the Pacific – important new evidence for agencies like the World Health Organization (WHO) advising on vaccines. The results will also support countries where the routine BCG programme is at risk of being neglected to assess the cost-effectiveness of the vaccine, as well as the effectiveness of TB vaccines in development.
TB is a major, and preventable, cause of death and disease which mainly affects the lungs. Two to three billion of the world’s population are infected with Mycobacterium tuberculosis, 10% of whom progress to clinical disease. In 2015 there were an estimated 10.4 million new cases of TB and 1.8 million deaths globally.
In the UK, BCG vaccination was given mostly to schoolchildren until it was discontinued in 2005 as the risk of TB was low. It has continued to be recommended to babies and infants who are at higher risk. Although offered around the world, the length of the BCG vaccine’s protective effect is unclear, something this new research aimed to address.
The study was conducted among adults in the general population in England 10 to 30 years after they were offered the BCG vaccine at school. It compared 677 people (cases) who were diagnosed with TB, with 1,170 people without a previous history of the disease (controls). Adults in both groups were inspected for BCG vaccination scars and asked about their vaccination history by specially trained interviewers. Overall, 75% of cases were vaccinated compared to 86% of controls. These groups had been matched on year of birth and the researchers controlled for social and demographic variables including drug use, education and living region.