May 14, 2020

BCG vaccination in childhood does not have a protective effect against COVID-19 in adulthood

By Denise Baez

NEW YORK -- May 14, 2020 -- People who received the Bacillus Calmette-Guérin (BCG) vaccine as babies have a similar rate of positive test results for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in adulthood compared with people who did not receive the BCG vaccination, according to a study published in JAMA.

The results suggest that BCG vaccination in childhood does not have a protective effect against coronavirus disease 2019 (COVID-19) in adulthood.

“Although the BCG vaccine is given to protect against tuberculosis, it has also been found to exert nonspecific beneficial effects such as protection against other infectious diseases and to enhance immunogenicity of certain vaccines, such as the influenza vaccine,” explained Ilan Youngster, MD, Shamir Medical Center, Zerifin, Israel, and colleagues.

The BCG vaccine was routinely administered to all newborns in Israel as part of the national immunisation program between 1955 and 1982, with greater than 90% coverage. However, since 1982, the vaccine was given only to immigrants from countries with high prevalence of tuberculosis.

“This change allowed comparison of infection rates and proportions with severe COVID-19 disease in 2 similar populations with differing BCG status: individuals born during the 3 years before and 3 years after cessation of the universal BCG vaccine program,” the authors wrote.

Dr. Youngster and colleagues looked at 72,060 SARS-CoV-2 test results done by real-time reverse transcriptase-polymerase chain reaction between March 1, 2020, and April 5, 2020. Results were stratified by birth year, and proportions and rates per 100,000 population of positive test results were compared between people born from 1979 to 1981 with people born from 1983 to 1985, the latter of whom were likely unvaccinated.

Results showed no significant difference in the proportion of positive test results in the BCG-vaccinated group (11.7%) compared with the unvaccinated group (10.4%; difference, 1.3%; 95% confidence interval [CI], -0.3% to 2.9%; P = 0.09) or in positivity rates per 100,000 (121 vs 100, respectively; difference, 21 per 100,000; 95% CI, -10 to 50 per 100,000; P = 0.15).

There was 1 case of severe COVID-19 requiring mechanical ventilation or intensive care unit admission) in each group. There were no deaths in either group.

“The strengths of this study are the large population-based cohort and the comparison of 2 similar age groups, thus limiting confounders to a minimum,” the authors concluded. “The main limitation is the inclusion of populations who were not born in Israel, with unknown vaccination status. However, immigrants from countries that vaccinate with BCG, within these age groups, are a minority (4.9% and 4.6% of the older and younger population groups, respectively) and should not be overrepresented in one group. In addition, the rates per 100,000 do not represent the positivity rate in the population, as persons tested were preselected based on reported symptoms.”

There are 2 ongoing randomised clinical trials testing whether the BCG vaccine, compared with a placebo vaccine, can reduce SARS-CoV-2 infection and disease severity in healthcare workers (NCT04348370 and NCT04327206).