"[Fat-soluble] vitamin A . . . became known as the 'anti-infective' vitamin."

Christopher Masterjohn calls fat soluble Vitamin A, aka, Retinol, the anti-infective vitamin.  And by anti-infective, he means anti-infection, meaning that it would protect you from infections?  Particularly the measles. "What about Vitamin C?  I thought that Vitamin C was the vitamin to take to stave off infections!" you insist.  The two focus on different components of your immune system.  Retinol Vitamin A protects your ". . . immunity, bone growth, mucous membranes and the eyes, skin, hair and nails." Mucous membranes are an important part of your overall immunity, protecting the cells and keeping pathogens from penetrating your cells.

Vitamin C, a water soluble anti-oxidant, works on other parts of your immune system, coalescing in a forceful attack against predatory pathogens to destroy infections.  Vitamin C and Retinol A should be taken in conjunction.  Both produce much better results in repair as you are recovering from any debilitating condition, whether it be pathogen or injury. 

BEST SOURCE of RETINOL VITAMIN A
Wikipedia explains that "Cod liver oil is a nutritional supplement derived from liver of cod fish. As with most fish oils, it has high levels of the omega-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Cod liver oil also contains vitamin A and vitamin D. It has historically been taken because of its vitamin A and vitamin D content. It was once commonly given to children, because vitamin D has been shown to prevent rickets and other symptoms of vitamin D deficiency."

BRIEF HISTORY OF VITAMIN A

Weston A. Price Foundation's Christopher Masterjohn explains that:

While vitamin K2 languished in obscurity, vitamins A and D continually traded places with one another as the favored vitamin du jour. The pendulum initially swung in favor of vitamin D because rickets was common in the early twentieth century while eye diseases resulting from vitamin A deficiency were rare. It then swung in favor of vitamin A when that vitamin became known as the “anti-infective” vitamin.2 After World War II, the medical establishment had easy access to antibiotics and thus lost interest in battling infections with vitamin A.3 Vitamin D fared far worse, taking the blame for a British epidemic of infant hypercalcemia and eventually earning a reputation as “the most toxic of all the vitamins.”4

These days, the pendulum has swung full force in the opposite direction: we blame an epidemic of osteoporosis on vitamin A, and see vitamin D as the new panacea.5

Though a paradigm of synergy never took hold, it was not for want of opportunity. When Mellanby and Green first demonstrated in the 1920s that vitamin A prevented infections, they concluded that vitamin D could not be “safely substituted for cod-liver oil in medical treatment,” and that “if a substitute for cod-liver oil is given it ought to be at least as powerful as this oil in its content of both vitamins A and D.”2 Consistent with this point of view, clinical trials in the 1930s showed that cod liver oil could reduce the incidence of colds by a third and cut hours missed from work in half.6 Cod liver oil also caused dramatic reductions in mortality from less common but more severe infections. The medical establishment, for example, had been successfully using it to treat tuberculosis since the mid-nineteenth century.7 Studies in the 1930s expanded this to the treatment of measles.8 These findings made the popularity of cod liver oil soar (Figure 1).9.