Regarding the BCG vaccine.....

Regarding the BCG vaccine, which of the following statements is true?

A) Foreign-born persons who received the BCG vaccine should never have a PPD administered.
B) The BCG vaccine is most efficacious for older adults, and children benefit much less from the vaccine.
C) A PPD in an individual with a remote history of BCG vaccine should be interpreted as if the BCG
had not been given.
D) The BCG vaccine is made from killed M. tuberculosis.

Answer And Discussion

The correct answer is “C.” A PPD in an individual with a remote history of BCG vaccine should be interpreted as if the BCG had not been given

The PPD should be interpreted exactly the same way in those who have
and have not had BCG.

“D” is incorrect. The BCG vaccine is made from attenuated Mycobacterium bovis.
“B” is incorrect. BCG is most efficacious in children but protection from the vaccine wanes over a
few years. Even in children, it is a poor vaccine, protecting children from TB only about 50% of the
time.

Persons vaccinated with BCG should still be evaluated by PPD (only if appropriate), and an increase
in induration >10 mm (age <35 years) or >15 mm (age ≥35 years) from baseline is considered
positive.

False-positive PPDs can be due to bacillus Calmette–Gu ´ erin (BCG) vaccine and infection with other mycobacteria. However, most patients who had the BCG vaccine will experience a decline in immunity (a maximum of 20% will have a positive PPD due to BCG 10 years after the vaccine was given).
If there is concern about a potential false positive test, an interferon gamma release assay should be performed.
False negatives occur when immunity is impaired. If you suspect impaired immunity, use an interferon gamma release assay.