Why it is important to vaccinate a human newborn within 24 hours since birth?
In the US, infants are vaccinated against Hep B at birth and again a month or two later as well, because of the risk of maternal transmission. If the mother is known to be HepB positive, HBIG will also be administered.


  Perinatal HBV transmission can be prevented by identifying HBV-infected (i.e., hepatitis B surface antigen [HBsAg]-positive) pregnant women and providing hepatitis B immune globulin and hepatitis B vaccine to their infants within 12 hours of birth.


The reason for the HBIG is obvious, but it doesn't last for life. Therefore, the vaccine and its booster.


  Hepatitis B virus (HBV) infection in a pregnant woman poses a serious risk to her infant at birth. Without postexposure immunoprophylaxis, approximately 40% of infants born to HBV-infected mothers in the United States will develop chronic HBV infection, approximately one-fourth of whom will eventually die from chronic liver disease.


In countries where HepB is not prevalent, there is little cause to immunize at birth. However, it is too common in the US.


  Preventing perinatal HBV transmission is an integral part of the national strategy to eliminate hepatitis B in the United States. National guidelines call for the following:
  - Universal screening of pregnant women for HBsAg during each pregnancy
  - Case management of HBsAg-positive mothers and their infants
  - Provision of immunoprophylaxis for infants born to infected mothers,   including hepatitis B vaccine and hepatitis B immune globulin
  -Routine vaccination of all infants with the hepatitis B vaccine series, with the first dose administered at birth  


The risk of HepB vaccine is low. The seriousness of the disease is high. It is not only the mother who might be a carrier. There are many unidentified carriers in the US. That makes the risk-to-benefit ratio low. Driving your newborn home in an automobile is probably more of a risk than the vaccine, but most people do so anyway, and do so many, many times over the course of the baby's life. 

In the US, we do not routinely vaccinate against TB, so I cannot address that issue with any degree of expertise. The risk-to-benefit ratio is not as low as for HepB. It is given to children who are continuously exposed to someone (say, a parent) with active TB, or in certain communities where TB is very prevalent. Obviously, if the risk of SCID (severe combined immunodefficiency) is high, the risk of the vaccine is much higher, and some infants have died from it.

Discussing the risk to benefit ratio of all infant vaccines is too broad for this venue.

Separating Fact from Fiction in the Newborn Nursery: Hepatitis B Vaccine for Newborns
The benefits and risks of bacille Calmette-Guérin vaccination among infants at high risk for both tuberculosis and severe combined immunodeficiency: assessment by Markov model