smallpox vaccine and vaccination in the intensified ... - libdoc.who.int

11. VACCINATION IN THE INTENSIFIED PROGRAMME 569
Development of the Bifurcated Needle
The bifurcated needle was the result of a developmental study by staff at Wyeth
Laboratories but the original idea can be traced back to the early 19th century (D. Baxby,
personal communicatio~, 1983). "This operation [vaccination] is usually perfdr&ed with-a
common lancet :but one which is fissured by a longitudinal slit, like a writing pen, succeeds
rather better" (Moore, 181 7).
Of the needle's more recent history, B. A. Rubin (personal communication, 1980)
wrote :
"In 1961, I started to test new methods of dispensing the vaccine while also considering
the methods of scarification. I collaborated with the Reading Textile Machine Com~anv
0 I I
(now a division of Rockwell International) in needle design. We experimented with
various textile needles and filament guides with standard openings as methods for
dispensing vaccine. It then occurred to me that a pronged needle would retain the capillary
activity of a loop, and that it might have simultaneous utility in scarification. I therefore
suggested the use of a sewing needle in which the loop end was ground down to give a
pronged fork. A system was devised in which a piece of wire was cut to the right length, and
then stamped to give the fork shape, with such dimensions so that the prongs would hold
exactly 1 mg of water by capillarity. The machine company then used a mass tumbling
system that could sharpen the prongs of the forks of large numbers of needles.
"The sharpened fork was retested and found to hold 1 mg of water quite firmly. When
tested with reconstituted lyophilized vaccine, the retained volume tended to be somewhat
greater because of the increased viscosity. But the liquid vaccine adhered firmly to the
needle. Thus, when the bifurcated tip of the needle is dipped into the vaccine, a constant
amount is suspended between the prongs, ready for inoculation."
vaccinator to learn. It became the standard
method of vaccination throughout the world.
It was observed that, if certain vaccinators
recorded more vaccination failures than expected,
it was often because they were too
gentle, partly because of the above-mentioned
belief that bleeding at the inoculation site
reduced the take rate. However, experience
showed that this belief was unfounded, and
vaccinators were advised to use the multiple
puncture method with the bifurcated needle
with enough force to cause slight bleeding.
Take rate. Tests carried out in Egypt, Kenya
and Liberia (Table 11.16) showed that take
rates by the multiple puncture method were
in the range of 98-100% in primary vaccinations
and that reactions specified as major (see
Chapter 7) occurred in 56-82% of revaccinations.
In experiments by Dr Shafa in Egypt, in
which the same individuals were inoculated
on opposite arms by different methods the
take rates for revaccination by scarification
were slightly lower than those obtained with
the bifurcated needle.
Amount of vaccine. The amount of reconstituted
vaccine taken up by the bifurcated
needle was tested in the ~mall~ox
unit in Geneva and the results were confirmed
in the field. It was estimated that one
dip of the needle point lifted an average of
0.0025 m1 of reconstituted vaccine between
the prongs. Since the amount of reconstituted
vaccine used in conventional vaccination was
about 0.01 ml, vaccination with the bifurcated
needle saved vaccine, permitting 4 times as
many vaccinations to be administered with a
given quantity of vaccine.
Design of the b$urcated needle. The original
needle developed by Wyeth Laboratories was
designed to be used once only and then
discarded. However, for the global eradication
programme it was essential to be able to
reuse the needles several times and to make
them as cheaply as possible. In collaboration
with a metallurgical firm, WHO investigated
methods of increasing the carbon content so
as to produce the hardest possible steel that
would not rust. When this steel was used,
metallurgical testing showed that there was
no change in the "hardness index" after a
bifurcated needle was flamed in a spirit lamp
up to 50 times, for 3 seconds on each occasion,
but that the index decreased considerably if a
Eradication needle was flamed for 5 seconds on 25 or more