PRELIMINARY REPORT (fa l) 
on the 
Vaccination of Man 
against 
Equine Encephalomyelitis (Western type) 
by 
The Neurotropic Virus Disease 
Commission 
of the 
Board for the Investigation of 
Epidemic Disease in the Army 
Submitted August 1st, 1942 At the meeting of the Commission on December 3rd, 
1941, the request was made by Colonel J. S. Simmons and 
Dr. P. G, Blake that evidence be weighed pro and con, with 
regard to the vaccination of troops against (epidemic) 
encephalitis. Information on the following points was desired;- 
I. Evidence (serological or otherwise) of the protective value 
of such vaccines. 
!!• Possible dangers in the use of such vaccines, 
III. Circumstances under which they might be used. 
IV. Directions for their administration. 
Inasmuch as most of the (epidemic) encephalitides are 
£ 
summer diseases, the Commission is submitting report (in 
preliminary form) at this time. It is only concerned with 
equine encephalomyelitis of the Western type (E.E.W.) and is 
largely concerned with one vaccine, viz. Lederle!s formallnlzed 
(chick embryo) vaccine. We are not prepared to discuss equine 
encephalomyelitis of the Eastern type (E.E.E.), St. Louis or 
Japanese B encephalitis, or other encephalitic viruses on which 
members of the Commission are working. 
It is obvious that the best means of answering major 
questions which have been posed would be to vaccinate large 
numbers (many thousands) of human volunteers with a variety of 
different vaccines and then to expose them to the disease so 
that one might compare the attack rate in the vaccinated groups 
with that of control groups in the same area. The opportunity for performing such an experiment is not yet available and, 
as a Substitute approach, we have chosen to observe the 
serological evidences of immunity which result in humans from 
vaccination against E, B.W. and to attempt to estimate what 
these serological evidences of immunity mean. 
!• Specific points bearing on this question are;- 
(a) Do persons given Lederlefs Western encophalomyelitic 
vaccine develop antibodies? 
(b) How soon do these antibodies appear? 
(c) What response may be obtained with a single dose of 
tho commercially available vaccine? 
(d) Does tho development of antibodies indicate that the 
vaccinated persons have become Immune? 
(a) Tho first question has already been studied at 
Duke University (1) where Beard ei: aL,, have reported on the 
speed at which neutralizing antibodies develop in humans vac- 
cinated against both E.E.W. and E.E.E# and tho duration of such 
antibodies, as well as the findings after a second vaccination# 
Response to their vaccines as measured by serum- 
neutralizing antibody-content, was moderate (viz. between 100 
and 10,000 mouse-infectious units - as determined by the intra- 
abdominal method) and more rapid for E.E.W. than E.E.E. 
(1) Beard, J.W., et al., J# Immunol. 38? 117, 1940, and 
lbid# 40: 4977 1941. 3 
The duration of these antibodies was maintained for E*E.W, 
at a fair level for at least 6—9 months. Revaccination at this 
time resulted in the Induction of neutralizing antibodies at 
levels 10 to 100 times higher than that noted with the Initial 
course of vaccine. 
Two more recent studies by the Commission (viz* 
by A. B. Sabin and his assistants, at the Hospital 
Research Foundation, Cincinnati, and by L« T* Webster and 
J. Casals, at the Rockefeller Institute) have given more 
information, as follows:- 
Experiment 1* Dec* 1941 - April 1942* Six volunteers 
wore chosen from New Haven, Conn*, (where presumably no cases 
of E*E*W* have ever been reported)# Each was injected with 2 
doses (1 cc. one week apart) of Ledorlefs (E.E.W*) vaccine Lot 
10K3A (2). Prom each vaccinoo a prevaccination and two post- 
vaccination specimens of blood were obtained* Tests on these 
specimens, (made by Webster and Casals) for both neutralizing 
and complement-fixing antibodies indicated that all individuals 
were negative prior to vaccination and that all developed 
neutralizing antibodies 18 to 21 days following vaccination* 
but failed to develop complement-fixing antibodies. (3). 
(2) The Commission is indebted to the Lederle Co. for this 
supply of vaccine. 
(3) A tabular report of these results was included in the 
Report of the Neurotropic Virus Commission made on 
May 15th, 1942* 4 
Experiment 2*. April 1942-July 1942, Vaccination 
in Manitoba. Canada, The Province of Manitoba experienced a 
severe epidemic of Western equine encephalitis during the summer 
of 1941, and in the fall of that year the decision was made by 
Dr# P, W. Jackson (Deputy Minister of Health) to vaccinate a 
group of (adult, males) farmers within the 1941 epidemic area. 
(See Appendix, Section A.) These vaccinations were performed 
(on a voluntary basis) again using Lederle*s vaccine (Lots 
-4B, -5A, ~6A, -8A and -9A) in May, 1942, and blood 
samples from 40 of the vacclnees were collected and sent by 
the Canadian authorities (4) to Dr, Sabin for neutralization 
tests. Dr, Sabin forwarded part of each specimen in the 
frozen state to Drs. Webster and Casals for the purpose of 
duplicate tests. 
Dr. Sabin found that before vaccination 22,5 per 
cent of the 40 persons had neutralizing antibodies against 
Virrs 
tias Western equine encephalomyelitis, while none of the 39 
sera tested had neutralizing antibodies against the virus of 
St, Louis Encephalitis* One week after administration of one 
dose of 1 c.c# of the vaccine, only 17 per cent of 30 persons 
who were originally without antibody became positive, but with 
one exception the neutralization indexes were low. At the end 
(4) The Commission is indebted to the Hon, James McLenaghen, 
Minister of Health, to Dr. P. W. Jackson, Deputy Minister 
of Health and to Dr. C. R. Donovan, Director, Division 
of Disease Prevention - Department Health and Public 
Welfare, Province of Manitoba, Canada for their generosity 
and efficient cooperation in allowing us to study their 
material and in collecting it and sending it to Dr. Sabin# 5 
of two weeks 46 per cent of the 13 people who received only 
the one dose of vaccine had neutralizing antibodies but only 
of moderate titro. On the other hand, all of 17 people who 
received an additional dose (1 c.c.) of the vaccine had neu- 
tralizing antibodies at the end of 2 weeks, and with but ono 
or two exceptions the tltres wore very high. 
Dr. Sabin concludes that the Lederle vaccine is 
adequate for the production of a high titre of neutralizing 
antibodies weeks when two 1 c#c. doses of the vaccine 
are used. Although no data were obtained to indicate what 
2 c.c. or more as a single dose might have done, this vaccine 
does not fulfill all of the desiderata of producing neutraliz- 
ing antibodies of moderate titre with one dose in one week. 
(See Appendix, Section B for details of neutralization 
experiments,) 
Duplicate tests by Webster and Casals indicated 
close agreement with Sabin’s neutralization tests and also 
that 2.5 per cent had complement-fixing antibodies in low 
titre prior to vaccination but that only an additional 5 per 
cent following vaccination# 
From these two experiments it is concluded that 
persons inoculated with two doses of the Lederle Western equine 
encephalomyelitis vaccine generally develop neutralizing anti- 
bodies of high titre but no complement-fixing antibodies. 6 
Evidence bearing on the last question (d), viz, 
whether the development of antibodies indicates that the 
vaccinated persons have become immune to the disease, has 
been sought from experiments on animals. Considerable data 
have already been collected on this point by Olltsky and his 
colleagues. (5) Although the species of choice for new 
experiments would probably be one which is naturally sus- 
ceptible to the disease, such as the horse, mice were 
selected because of their availability in large numbers and 
the intracerebral route of infection was the first studied 
because of its uniformity of response. A series of such 
experiments have recently been performed by Drs, Webster and 
Casals, They are recorded in the Appendix, Section C, In 
brief these tests consisted in the vaccination of mice with 
both live and formalinized vaccine and subsequently testing 
the resistance of these mice to intracerebral inoculation 
and comparing this resistance with the titre of antibodies 
(both neutralizing and complement-fixing) found in the blood 
of the vaccinated animals at stated times. 
On the basis of these “severe“ tests, Webster and 
Casals have suggested that the titre of complement-fixing 
antibodies may parallel the degree of developing immunity 
(5) Morgan, I,M. and Olitsky, P,K,, J. Immunol., 42: 445,1941; 
Morgan, I.M,, J. Exp, Med,, 74: 115, 1941 ancT"Schle singer, 
R.VJ,, Morgan, I.M., and Olitslcy, P*K,, J.A.M.A. 119; 618, 
1942, 7 
more closely than do neutralizing antibodies. It should be 
mentioned, however, that there are no experiments reported on 
resistance developed to peripheral inoculation of virus, which 
may perhaps simulate more closely the "natural mode of infec- 
tion". It is possible that a minimal amount of circulating 
antibody is associated with peripheral resistance but only a 
high degree of immunity is associated with cerebral resistance^ 8 
II. Dangers of. and reaction to. the Vaccination. Inasmuch 
as the vaccine used on humans in this series of observations 
was formalinized (and not live) virus, the dangers of inducing 
an experimental infection arc not groat. 
In the studies by Beard at al., (1) it was reported 
that general aand local reactions to the initial course of vaccine 
(2 doses 2 c.c. each) were mild or absent (incidence not mentioned) 
except in one instance (1%) in which muscular stiffness of at least 
4 months duration developed subsequent to vaccination. Reaction 
to the second course of vaccine (single dose 2 c.c.) were reported 
by the Boards to be "definitely greater than that to the first". 
This consisted in “malaise, slight rnausoa and weakness. In 
several instances cramping stiffness and indefinite muscular sore- 
ness in the lower thigh on the side of injection wore felt, which 
persisted in 1 case (out of 9 in the series) several weeks, diminis 
ing gradually and entirely disappearing finally. Local reactions 
at the site of injection wore not seen.” 
The Manitoba vaccination experiment has now given us a 
much larger group of people vaccinated (for the first time) and 
tho report to date (6) on those is that of approximately 3,000 
people given tho vaccine, about 1600 reports are now available. 
Of those approximately 114 persons (7$) wore reported to have had 
both local and general reaction following the first dose and about 
288 (12$) had both local and general reaction following tho second 
dose. None of these reactions wore serious insofar as could be 
ascertained and no one required treatment by a physician. 
(6) Dr. C. R. Donovan has kindly reported the findings to me a 
of the date of July 23, 1942. 9 
III. Circumstances under which the vaccine might be used. 
In spite of limited knowledge, vaccination would still 
seem to be a preventive measure worth trying under certain cir- 
cumstances smhA, as stated in the Commissions report of May 15th, 
1942, thft for frfeo -uoq of Lodorloto ffoaamQlfrftigQd ohiefr 
may-bo t 
Vaccination is only one of several measures which may 
be put into effect as possible control measures in this disease. 
Chief stress should be placed on Sanitary Corp activities, which 
i 
should exert all preventive measures possible whenever cases of 
critically diagnosed E.E.W. are occurring in the civilian popu- 
lation in the neighborhood of Army establishments. When, and 
only when at least 2 or 3 definitely diagnosed cases have occurred 
should vaccination be contemplated and then offered on a purely 
voluntary basis. 
More specifically, the vaccine can be used when E.E.W# 
which has been diagnosed with reasonable accuracy appears in a 
given area in epidemic form. This would be regardless as to 
whether other types of encephalitis may bo suspected or proven 
to be present within the same epidemic area at the same time. 
Under these circumstances, it would seem wise to regard all 
troops within such an epidemic area as possible candidates for 
vaccination — but particularly troops on manoeuvres which are 
apt to have more exposure to mosquitoes than other groups. 
'"’No specific reports are as yet available as to the reactions 
to this vaccine in men who are on active duty and undergoing 
a moderate amount of physical strain, but to all intents and 
purposes this was the case with a fair percentage of the 
farmers vaccinated in Manitoba in May, 1942. 10 
'inasmuch as tho amount of vaccine at present available (for 
purchase) is not large (and the time required for its production 
of new vaccine is about 40 days) no large-scale vaccination 
program can be planned by the Army this summer, but it is pro- 
posed that if and when it is necessary to keep troops within 
certain epidemic areas or to move troops into such epidemic 
areas, wo believe that tho vaccino should bo administered on 
a voluntary basis to as largo a group as is practical. Y/e 
believe that under such circumstances, if tho number of men 
volunteering to bo vaccinated should bo over 50, that tho 
Commission should bo notified and that one or moro of its 
members should assist in tho "experiment", Every effort 
could then be made to follow the vaccinated group and to 
compare their disease record with that of unvaccinated con- 
trols. 11 
IV. Diroctions for Administration of Vaccine, Thoro arc 
no indications that tho technique of administering Loderlo!s 
chick embryo vaccine (E.E.W.) should be altered from those 
used in the Canadian experiment, viz* that 2 doses bo employed, 
1 c.c. each, and that they bo given one week apart. 
Respectfully submitted. 
John H. Paul 
Director, Commission for 
Neurotropic Virus Diseases,