CHAPTER IV._A Practical Treatise on Smallpox

VACCINATION.

Vaccination consists in the inoculation of virus taken from the pock

produced by vaccinia.

*Vaccine Virus.*--Virus has been taken from vaccine vesicles on almost

all animals susceptible to vaccinia, but throughout the greater part of

the last century the material used in the vaccination of human subjects

was taken generally from a vaccine vesicle on the arm of a previously

unvaccinated healthy child. Such virus when collected at the proper

time was found to take with great regularity, and vesicles resulting

from its use were uniformly well developed and typical. Humanized

virus was, however, open to the objection that it could communicate

disease if the child were not perfectly healthy, and as a matter of

fact it did communicate syphilis in a certain number of instances.

The possibility of this infection was so serious an objection to the

use of virus from this source that in the last quarter of the century

calf virus, recommended and used in Italy many years before, was

gradually substituted for human virus, and at the present time the

use of animal virus is general in Europe and in the United States. In

the production of virus, calves are for commercial reasons generally

preferred to other animals. Calves take typically, and a large amount

of virus can be collected from them, whereas all other animals either

are comparatively expensive, or take poorly, or are able to furnish but

little virus. Cows also are more expensive, are less easily handled,

and develop vaccine vesicles less typically.

In the practical production of vaccine virus calves are vaccinated

much as human beings are vaccinated, but over a larger area. Usually

the posterior abdomen and the insides of the thighs are covered with

superficial linear incisions, and into these incisions the seed virus

is rubbed. In the laboratory of the New York City Health Department

all operations relating to the vaccination of the animals and to the

collection of the virus are carried on in an operating-room provided

with a cement floor, glazed brick walls, and equipped with enamelled

metal operating furniture, such as would be used in a hospital. The

attendants wear sterile gowns and the technique of the operations is

aseptic. The seed virus is either humanized virus collected by touching

sterile pieces of bone to the serum exuding from ruptured vesicles

on the arms of children, or in the great majority of cases bovine

glycerinated virus which has been preserved two months or longer.

It is found that the crust of the vesicle, the serum issuing from the

vesicle after the crust is removed, the pulp which forms the semi-solid

contents and base of the vesicle, and the serum which exudes from the

base of the vesicle after the pulp has been removed by a curette,

all convey material capable of producing the vaccine vesicle in a

susceptible person, and are therefore all different forms of vaccine

virus. It has been shown, however, that if any of this material is

filtered, so that all the solid particles are removed, the filtrate is

inefficient. In other words, the serum is efficient as vaccine virus

simply by virtue of the solid particles which it contains. It is also

found that the pulp is so rich in the active principle of vaccine virus

that it may be mixed with several times its weight of glycerin or other

diluent and still maintain its efficiency.

The different sorts of vaccine virus on the market are simply different

ways of supplying this material coming from the vesicle. Most material

is in one of three forms,--

(_a_) The pulp diluted with some excipient, such as glycerin, vaseline,

or lanolin. The emulsion, made by mixture with glycerin, may be

contained in a vial or in a capillary tube, or may rest on some holder,

such as an ivory or bone point. In the latter case the point is usually

protected by some form of cap. Mixture with vaseline or lanolin makes

a paste, which is usually issued in a box. This is in use in parts of

Italy and in India.

(_b_) The serum dried on a holder, as an ivory or bone point or a quill.

(_c_) The serum mixed with some excipient, usually solid or semi-solid,

until it becomes a paste, and furnished like dried serum on a holder.

For a physician the choice among these three forms is governed by

considerations of efficiency, safety, and ease of use. All the forms

are under certain conditions efficient, but comparative tests show that

the emulsion of the pulp issued by different laboratories is much more

certainly efficient than the other forms, and the glycerinated emulsion

is at present in most general use both abroad and in this country.

It is also true that all forms may be perfectly safe. All forms

contain bacteria when prepared, and the majority of these bacteria

die within a few weeks or months after preparation. On account of the

mildly antiseptic quality of glycerin the bacteria in the glycerinated

emulsion usually die sooner than those in the other forms of virus,

and so far as bacteria are objectionable in the virus the glycerinated

form may therefore be said to be somewhat preferable. It should be

added, however, both that glycerinated virus is usually put in the

market before the bacteria have disappeared and that the bacteria

present in virus issued by well-conducted laboratories are not found

to be pathogenic to persons when inoculated by the customary method of

vaccination.

The ease of use of any form of virus depends largely upon the custom of

the physician. In vaccinating a large number at one time there can be

no question that the use of a liquid virus supplied in vials is more

rapid than the use of a dried virus, as the latter has to be thoroughly

moistened before it can be applied effectively.

*Methods of Vaccination.*--The usual method of vaccination is to

scarify a spot on the skin and to rub the virus on that spot. The

choice of place depends partly on æsthetic reasons and partly on

convenience. To avoid the formation of an unsightly scar on the arm,

the leg may be used instead. If the arm is chosen, the insertion of

the deltoid is the place of election on account of the small number of

lymphatics there. If the leg is chosen, the area just below the head of

the fibula presents the same anatomical advantage; but a spot a short

distance above the knee on the outside of the thigh is often thought

to offer less opportunity for injury and infection. Choice between the

sides depends in an adult on the use to which the vaccinated limb is to

be put, and in a baby on the advantage of vaccinating the side which is

carried away from the nurse.

The size of the scarification is important. The vesicle is always

somewhat larger than the scarification, and the larger the vesicle the

greater danger that the surface may be broken, and the more opportunity

there is for the introduction of extraneous infection. A spot as

large as the head of a medium pin is about as small as can be easily

scarified, and vesicles formed on such scarifications are least liable

to have inflammatory complications. If, as certain evidence tends to

show, a larger area of scar guarantees greater protection, and if a

larger area is therefore desired, it is better to vaccinate in two or

three small spots than in one large one. It is somewhat difficult to

rub the virus from a bone point on a spot of the minute size described,

and as this form of virus is usually more dilute than glycerinated

virus, a larger area may safely be employed.

The scarification may be made with any sharp instrument, or with the

point itself. The only precaution necessary is that the instrument

should be free from infection. As a scarifier the ordinary cambric

needle presents the advantages that it is usually clean, is easily

sterilized, and is so inexpensive that a fresh one can be used for

every operation.

It is not necessary that the scarification should draw blood, although

blood is not objectionable unless it flows so freely as to wash away

the virus, or unless the subject has hæmophilia.

Although with a notably susceptible subject or with especially active

virus it may be sufficient simply to smear the virus on the scarified

area, it is usually necessary and always advisable to rub in the virus

with a wooden slip or with the point firmly and thoroughly.

Other methods of introducing vaccine virus are by puncture, by deep

injection, and by the mouth.

In the method by puncture either a grooved lancet or a hollow needle

may be used. A shallow puncture is made and the virus is deposited in

it. The resulting vesicle is usually small and nearly circular, and

generally remains free from infection; but as the hole in which the

virus is placed is small, it is possible that the issuing blood may

wash it away completely, and the percentage of success with this method

of inoculation is not quite so large, even in careful hands, as by

the process of scarification with the same virus. Animal experiments

with deep injection of virus through a hypodermic syringe and with

administration of virus by the mouth show that there is no certainty of

successful vaccination by these means, and that when success results

there is no proof of it without a subsequent vaccination on the skin to

test or to demonstrate the immunity.

*Care after Vaccination.*--As vaccination is a surgical procedure, it

should be conducted aseptically with a sterile instrument on clean

skin, and the wound should be guarded against extraneous infection.

It is well therefore to put either a sterile gauze cover or a clean

shield over the wound as soon as the virus has been sufficiently

absorbed, and to leave the protection on until the natural crust has

been formed,--_i.e._, for a few hours. If the guard could be kept

in position without motion and also without injurious pressure, it

might remain until the process ended with the formation of a scar and

the exfoliation of the crust; but practically it is so certain that

the guard will be moved that it is wise to remove it and to trust

to the protection of a clean muslin or linen cloth attached to the

loose sleeve or other undergarment. For a day or two at the time when

the inflammation is at its height it may be well again to guard by

a shield against injury from a blow or push, but the shield should

always be regarded as itself a danger. If by any accident the vaccine

pustule becomes infected, it should be treated like any other infected

wound,--the crust removed, the ulcer cleansed with antiseptics and

dressed surgically. The immunity given by the pock is not at all

lessened by this treatment.

*Normal Clinical Course.*--After primary vaccination in man there is a

stage of incubation lasting for from forty-eight to seventy-two hours;

a papule then develops, and by the end of the third or fourth day

this has begun to show umbilication and a vesicular structure. When

fully developed, about the sixth day after vaccination, the vesicle is

distended and pearly in color. On the seventh or eighth day the areola

develops,--_i.e._, the skin about the vesicle becomes hard, sensitive,

and red, the redness extending a variable distance, not usually more

than two inches from the edge of the vesicle. In the course of the next

day or two the vesicle loses its pearly appearance and becomes opaque

and often slightly yellow. With the development of the areola and of

the pustule the adjacent lymph glands may swell and become somewhat

painful; there may also be constitutional derangement,--some fever,

pain, anorexia, restlessness, and more or less prostration; there is

usually a moderate leucocytosis. About the eleventh or twelfth day the

areola begins to fade, the constitutional symptoms to subside, and

the pustule to dry up. A dark crust is formed which drops off usually

between the eighteenth and twenty-fifth days, leaving a rosy depressed

scar on which not infrequently a secondary scab is formed, to be shed a

few days later.

*Variations in the Clinical Course.*--The vesicles may appear on the

second day, but it is more frequently delayed until the fourth, fifth,

sixth, seventh, or even the eighth day, and cases have been observed in

which the delay was even longer.

The areola, which should be bright red, may be purple, and may extend a

long distance from the vesicle.

The pustule may be hemorrhagic or may be filled with greenish pus; in

this case there is probably a mixed infection.

Sometimes instead of a vesicle there appears a hard elevated nodule, in

color like a red raspberry. With this there is usually no areola, and

no constitutional symptoms develop. The growth is usually an evidence

of poor virus. It may persist for some time before absorption.

The course may be abortive,--_i.e._, the vesicle does not develop

completely; pustulation comes early and the crust is shed and the scar

formed before the end of the second week. This course is normal though

not invariable in revaccinations.

The scar may be poorly marked, even when the vaccination has run a

typical course.

*Complications.*--The most frequent complications are infections and

eruptions. An infection may be, of course, of many sorts. It may be,

for example, the streptococcus of erysipelas, or the bacillus of

tetanus, but it is oftenest a skin coccus. These infections may be

introduced with the virus, with the instrument, or later through wounds

in the vesicle or pustule. Erysipelas and tetanus following vaccination

are exceedingly rare, and it has never been shown that in a case of

tetanus the germ was inoculated at the time of vaccination.

Eruptions are probably usually due to a chemical irritation produced by

the development of the vaccinia; they are analogous to the eruptions

following the injection of antitoxine and the ingestion of various

drugs. They vary in appearance, sometimes resemble the eruption of

measles or of scarlet fever, and again are urticarial; they are

macular, papular, and vesicular.

When a moist eczema is present there may be auto-inoculation of the

pock on the affected area and a general confluent vaccine eruption

appear.

*Immunity.*--The immunity against smallpox, or vaccinia, produced

by vaccination is of gradual growth, and is not complete until the

period of suppuration, about the beginning of the second week. Natural

immunity is said to exist, and is probable, but it is exceedingly rare.

Vaccination of a pregnant woman rarely, if ever, confers immunity on

the fœtus.

*Duration of Immunity.*--Sometimes a single vaccination gives immunity

for life. Usually, however, susceptibility returns at latest seven

to ten years after vaccination, and the second vaccination may give

immunity for the rest of the lifetime, or susceptibility may return

again and again. Failure of active, properly inserted virus shows only

that the person so vaccinated is at that time immune, but conveys

absolutely no information about the condition a few months later. The

appearance of the scar is not a trustworthy guide as to immunity.

Susceptibility to vaccination returns frequently within one year, and

has returned in three months from the time of a successful vaccination.

Susceptibility to smallpox probably returns, as a rule, later than

susceptibility to vaccinia. It is rare that a case even of varioloid

occurs within five years of a successful vaccination.

*Conclusions.*--Every child should be vaccinated at the time of

election during the first year of life, and should be revaccinated

before beginning school-life with its possibility of exposure.

Every person, no matter at what age, should be vaccinated at a time

of possible exposure to smallpox unless he has been successfully

vaccinated within three months.