016 - Combined Vaccination with Multiple Vaccines (Quadruple, Quintuple, and Sextuple)

One thing I hear from people who question the safety of vaccines is that too many at once may be harmful. This seems implausible, given the vastly larger number of antigens (material recognized as foreign by the immune system) that a person is exposed to in daily life every day.

It seems that even in the early 20th century, people (with reason) questioned the effectiveness of combining antigens from multiple into a single injection. So this study tested the antibody response and adverse reactions of different combinations of bacterial pathogens.

The study tested tetra-valent, penta-valent, and hexa-valent (that is, containing antigens from 4, 5, or 6 bacteria) vaccines in rabbits and people. Typhoid and paratyphoid A and B were present in all combinations, but some also had Vibrio cholerae (which causes cholera), Brucella (which causes Malta fever or brucellosis), or Yersinia pestis (which causes plague).

With all of them, they found that the levels and pattern of antibody responses were similar to those seen when vaccines were given containing only one of the organisms at a time, so there was no deficiency of antibody response.

Regarding adverse reactions, all of them seemed to cause local reactions (redness, inflammation) and general reactions (fever, malaise, pains) for 1-2 days, but the combos containing plague were much more severe. They noted that the combo vaccines with plague actually caused less severe reactions than plague vaccine by itself though. But of those without plague, more than 120,000 people (military folk) received some combinations without any more serious effects. So the authors conclude that the combination vaccines are safe and effective, and much more convenient than monovaccines, especially in tropical military settings.

Citation: Castellani, A. & Taylor, F. Combined Vaccination with Multiple Vaccines (Quadruple, Quintuple, and Sextuple). Br Med J 2, 356–359 (1917).