Post00316 ESTIMATING WASTAGE FACTORS 29 January 2001
CONTENTS
1. ESTIMATING VACCINE WASTAGE FACTORS Continued
In Technet Post00311, ESTIMATING VACCINE WASTAGE FACTORS, 15 January 2001, a
discussion on estimating vaccine wastage and vaccine wastage factors was
posted. The context of the discussion was the need for GAVI, the Global
Alliance on Vaccines and Immunization, to look at vaccine wastage - with its
potential for enormous unsustainable vaccine costs. The other discussion
context was and remains the need for national programs to monitor and
appropriately manage vaccine wastage to contain costs and enhance program
sustainability.
In today's posting, Robert Steinglass, BASICS, provides some clarification
and suggests that the order of the messages posted was misleading. Robert's
final paragraph was not copied to Technet and was not posted - it does help
a lot.
Julie Milstien, WHO/ATT, Souleymane Koné¬ WHO/AFRO, and Bob Davis, UNICEF,
Anton Luchitsky, PATH, and Hans Everts, WHO/EPI, add to the discussion.
Opinion, comments and additions please: [[email protected]][email protected][/email]
or use your reply button
___________________________________________________________________________
Moderators Note
Apologies to Technet Forum subscribers if it was difficult to make sense of
the discussion(s) in Post00311. The messages were grouped thematically, as
some messages were on estimating wastage factors while others were related
to methods of estimating wastage and the feasibility of programs routinely
estimating wastage. It seemed to make more sense thematically rather than
chronologically.
The final versions of the formula for the calculation of wastage factors as
modified by Robert Steinglass was posted as the lead item in the discussion
in Post00311 and is repeated below.
Our thanks to Michel Zaffran, WHO/V&B, who kindly translated the message
from Souleymane Koné¡Š___________________________________________________________________________
Date: Fri, 19 Jan 2001
From: "Robert Steinglass"
To: [[email protected]][email protected][/email]
Subject: calculation of wastage FACTORS (not rates)
Dear Allan,
I think an important point may well be overlooked, but first a quick
divergence to correct the record.
The order in which the postings appeared in the last TECHNET Forum is
misleading. The wastage formula which is posted at the start is what
emerged after I provided edits on an earlier version of John Lloyd's
formula. Therefore, my critique which comes immediately after the formula
does not make a lot of sense, since I am critiquing a different formula than
the one which appears.
The real point which is worth stressing to the TECHNET readers and should
not be overlooked is that the proposed wastage formula would be used to
directly calculate wastage FACTORS, thereby bypassing calculation of wastage
RATES.
* Missing from the thread of e-mails was my following comment to John Lloyd,
which may shed light for TECHNET Forum readers on the new proposed formula:
"The alternative to estimating vaccine wastage which I like best is what
they do in the NIS. They directly derive a wastage factor (which is much
easier to do arithmetically and which is the key coefficient which is really
needed to forecast vaccine requirements). They don't bother with
complicated calculations of wastage rates which would have to be converted
in any event into wastage factors. So they can tell you from their stock
records that, e.g., 1.5 doses of DPT were required to administer a single
dose. Pretty simple."
Robert
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From: [[email protected]][email protected][/email]
Date: Tue, 16 Jan 2001
Subject: RE: Post00311 ESTIMATING VACCINE WASTAGE FACTORS
To: Technet Moderator
I have to agree with Mark. Trying to develop hard and fast rules for
calculations for all situations is a fruitless expenditure of time. No one
understands the use of a formula better than someone who has figured it out
for him or herself.
However, it would be useful for GAVI to standardize what they want reported
and the considerations that would determine how it was calculated (stock
levels, vials lost because of expiry or cold chaing break, etc).
I am confused in this discussion because although the dates look like the
order is chronological, it also looks like John's first message is his final
word or else I cannot find his final word. What are you trying to say,
bottom line, John?
Dr Julie Milstien
Coordinator, Access to Technologies
Department of Vaccines and Biologicals
World Health Organization
20 Ave Appia Room M231
1211 Geneva 27 Switzerland
tel 41 22 791 3564
fax 41 22 791 4384
email [[email protected]][email protected][/email]
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Date: Tue, 16 Jan 2001
From: [[email protected]][email protected][/email] (Robert Davis)
Subject: Re:Post00311 ESTIMATING VACCINE WASTAGE FACTORS
To: Technet Moderator ,
Dear All,
I like a very simple method: Usage is doses administered/doses used or
discarded. Wastage is 100 % minus usage. This is very simple to calculate,
requiring only one division and one subtraction, well within the
intelligence levels of agency directors, for example.
Bob Davis
UNICEF/Nairobi
---
From: Souleymane Koné ¦lt;[email protected]>
To:
Subject: Re: Post00311 ESTIMATING VACCINE WASTAGE FACTORS
Date: Fri, 19 Jan 2001
Dear Allan,
Would you pleased translate my contribution to this important issue.
[The English version of the text follows. Our thanks to Michel Zaffran,
WHO/V&B, who kindly translated this message over the weekend!]
Le present sujet sur l'estimation des facteurs de perte des vaccins est
d'une importance capitale.
De facon general, deux indicateurs mesurent les pertes de vaccins: le taux
de pertes et le facteur de pertes.
Les deux indicateurs sont en fait lié³ et peuvent etre obtenus l'un a partir
de l'autre. Ce qui en mon sens les differencie c'est l'utilisation pratique
directe de l'un ou de l'autre dans la gestion des vaccins.
Le facteur de perte sera plus utilise dans la planification pour le calcul
des besoins en vaccins. En d'autres termes de combien de doses de vaccins
aurai-je besoin pour chaque cible a vacciner.
Le taux de perte indiquera plus facilement l'efficacite dans l'utilisation
des vaccins. En d'autres termes quelle proportion des doses de vaccins
destines a notre cible ne l'atteignent pas effectivement, c'est-a-dire
perdue. La gestion du programme devrait bien entendu rechercher les sources
et les causes des pertes afin de les minimiser.
Pour l'estimation des indicateurs de perte des vaccins (taux ou facteur de
pertes) ci-dessus mentionnes, l'essentiel reside dans l'esprit, dont les
formules ne sont (devront etre) l'illustration.
Ainsi la "premiere formule" de John du facteur de pertes est correcte:
Fw = ((B+C) x D)/A, le taux de pertes sera donc: Rw = 1 - A / ((B+C) x D)
Cependant deux clarifications sont necessaires:
1. le numerateur ((B+C) x D) devra tenir compte des differentes tailles de
flacons utilisees sur le terrain (observations faites par R. Steinglass).
Certains pays utilisent pour certains antigenes differentes tailles de
flacons (10 doses et 20 doses). Dans pareils cas les informations sur le
nombre de flacons correspondant a chaque taille devra etre disponible pour
les calculs. Ainsi le numerateur sera:
{(B1+C1) x D1 + (B2+C2) x D2) + ...}
ou:
B1 = nombre de flacons de taille 1 ouverts pour utilisation
C1 = nombre de flacons de taille 1 abimes pour
D1 = nombre de doses par flacon de taille 1
B2 = nombre de flacons de taille 2 ouverts pour utilisation
C2 = nombre de flacons de taille 2 abimes pour PCV, ch. froid
D2 = nombre de doses par flacon de taille 2
2. le denominateur: A (nombre de doses administrees) devra etre relatif a la
cible vaccinee. Si c'est le cas dans certains pays la vaccination des hors
cibles atteint parfois selon les antigenes 10 voire 15% du total vaccine,
par consequent les doses administrees aussi. D'ou une sous-estimation du
facteur de perte des vaccins si on utilisait au numerateur le nombre de
doses administrees (total population vaccinee) au lieu du nombre de doses
administrees a la cible (total cible vaccinee).
La "deuxieme formule" de John: Fw = ((B+C-D) x E)/A, est aussi correcte, et
le taux de pertes sera de: Rw = 1 - A/((B+C-D) x E)
Cependant le contenu du terme "C" (nombre de flacons sorties du depot for
utilisation) devra etre plutot "nombre de flacons recus".
Le numerateur ((B+C-D) x E) designera la quantite de vaccins mobilises pour
la vaccination.
Les memes observations faites pour la premiere formule s'appliquent pour la
deuxieme.
Meilleures salutations
Souleymane
___________________________________________________________________________
English version of Souleymane Kon駳 message.
Dear Allan,
The issue of how to estimate vaccine wastage rates is a most important one.
Generally speaking, two numbers can be used to measure vaccine wastage: the
wastage rate and the wastage factor.
The two numbers are related and one can be calculated from the other. In my
opinion what differentiates the two numbers is how they are actually used in
practice to manage vaccine stocks.
The wastage factor is normally used to plan and calculate the quantities of
vaccines needed. In other words: "how many doses of vaccines will I need for
a given targeted population?"
The wastage rate indicates more directly the efficiency of vaccine use. In
other words, which proportion of vaccine doses do not get used for the
target population and is wasted.
The programme management must of course identify the reasons and causes for
this wastage in order to minimise them
In order to calculate the two numbers, the most important is their meaning
rather than the formula:
John?s first formula for the wastage factor is correct:
Fw = ((B+C) x D)/A,
The wastage rate will therefore be:
Rw = 1 - A / ((B+C) x D)
However two clarifications are necessary_
1. The numerator: ((B+C) x D) must take account of the different vial sizes
used in the filed (this was pointed out by Robert Steinglass). Indeed, some
countries use, for certain antigens, different vial sizes (10 and 20 doses).
In these cases, the number of vials of each type of vial size should be
available for the calculation. The numerator will therefore be:
{(B1+C1) x D1 + (B2+C2) x D2) + ...}
Where
B1 = number of vials of size 1 opened for use
C1 = number of vials of size 1 with VVM expired
D1 = number of doses in vials of size 1
B2 = number of vials of size 2 opened for use
C2 = number of vials of size 2 with VVM expired
D2 = number of doses in vials of size 2
2. The denominator: A (number of doses administered) should be adjusted to
the number of doses actually administered to the target population. In some
countries and for some antigens, the group vaccinated includes sometimes 10
to 15% of children, which are not in the target group. Therefore the number
of doses actually administered may be 10 to 15% higher than those really
administered to the target group. If we were to use the number of doses
administered, without adjusting for target population, the wastage rate
would be under-estimated
John?s second formula:
Wastage factor Fw = ((B+C-D) x E)/A, is also correct and the wastage rate
will be Rw = 1 - A/((B+C-D) x E)
However, the meaning of "C" (number of vials taken out of stock for use)
should instead be "number of vials received" the numerator, ((B+C-D) x E)
then will refer to the total quantity of vaccine used for the vaccination
session
Best regards
Souleymane Kone
---
From: "Anton Luchitsky"
To: "Technet Moderator"
Subject: Re: Post00311 ESTIMATING VACCINE WASTAGE FACTORS
Date: Tue, 23 Jan 2001
Dear colleagues,
Agreeing with Mark Weeks's observations (particularly about the importance
of keeping indicators simple) I would like to mention that in Ukraine use of
a very simple indicator, namely vaccine wastage coefficient (total doses
used divided by the total number of vaccinations given during a specified
period of time) has proved to be very valuable; we demonstrated that over
the past 1-2 years wastage of vaccines decreased considerably as a
result of changes in immunization practices (grouping of children for
immunization session, arranging outreach sessions, etc.) as well as more
rational distribution of vaccines and prompt investigation of causes of high
wastage. Both the numerator (doses used) and denominator (vaccinations
given) are routinely recorded in monthly reports prepared by health settings
involved in immunization and subsequently analyzed at immunization points,
in rayons and at higher levels (oblast, MoH).
When developing this indicator the local working groups of experts decided
that the numerator should include the sum of doses utilized during
immunization and doses written off (e.g., frozen or expired), the latter at
the time believed to be insignificant and quite rare. It is possible that
the working group may decide to recommend separate recording and routine
analysis of the proportion of written off vaccine (in unopened vials).
Vaccine wastage coefficient can work very well if the country (or oblasts)
predominantly use only one presentation of a given vaccine, which is often
typical in cases of centralized procurement of biologicals.
The accuracy of this indicator may be to some extent compromised when
vaccine in various presentations (e.g. in 2- and 10-doses vials) is used on
the same territory; besides, it is difficult to "compare" wastage if one
rayon is using 2-dose vials and another one 10-dose vials.....
Whereas it is technically possible to account for different vial sizes when
calculating wastage(s), the added complexity may not be always justified -
immunization managers are mainly concerned about the price of one
vaccination and not about the wastage itself.
Here is a possible way out for the situation like this
1. Continue monitoring "average" wastage coefficient for given
rayons/oblasts as described above.
2. Determine the "average" price of one dose of vaccines used on the given
territories during the given period. [for example oblast X used 40,000
doses DPT during a 6-month period: 30,000 doses ($0.12 each) in 2-dose
vials and 10,000 doses ($0.08 each) in 10-dose vials). The average price
of one dose was (30,000 x 0.12 + 10,000 x 0.08)/ 40,000 = $0.11
3. Multiplying "average" wastage coefficient by "average" price of one dose
determine the cost of one immunization given on this territory.
4. Analyze the correlation between average price of one dose and average
wastage on the given territory. Determine the optimal proportion of vial
sizes for this territory [increase of the average cost of a dose due to
increased proportion of smaller size vials is only justified as long as this
results in decrease of the average wastage coefficient by the same degree or
more].
Best wishes,
Anton Luchitsky, M.D.
Program Officer
Program for Appropriate Technology in Health (PATH)
Khreshchatyk St., 29, Apt. 50 Kiev, 01001, Ukraine
Phone: (380)-44-462-0366 FAX: (380)-44-462-0365
E-mail: [[email protected]][email protected][/email]
Visit the PATH Web site at http://www.path.org
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To: [[email protected]][email protected][/email]
Subject: RE: Post00311 ESTIMATING VACCINE WASTAGE FACTORS
Date: Thu, 25 Jan 2001
Dear Allan,
I just read the discussion in Technet Forum 00311. I hope my comments do not
come too late or are dealt with in the attachments mentioned in the
discussion.
Whenever it says 'Doses administered' it should say 'Doses administered
according to EPI schedule'. A dose given to the child at the wrong age group
is a wasted dose.
The C in John's second formula should not be the number of doses issued from
the store, because that would lead to a double count, since they are
included in the number of vials in stock. The C should be the number of
vials received over that period. The formula would then be:
((B + C - D) x E) - A)/ A x 100,
A = Number of children immunized according to EPI schedule over period Y
B = Number of usable vials in stock at the beginning of period Y
C = Number of vials received during period Y
D = Number of usable vials in stock at the end of period Y
E = Number of doses per vial
An inconvenience of calculating on basis of vials rather than doses is that
remaining doses in opened vials will be counted as lost even though they may
be used the day after the inventory was made. In smaller health centres,
where few vials are used, that may have an important impact on the wastage
rate.
Regards
Hans Everts
Technical Officer
EPI
WHO Geneva
Tel: 00 41 22 791 3683
___________________________________________________________________________
ESTIMATING VACCINE WASTAGE FACTORS Robert Steinglass' final version
1. Using National (or Sub-national) Records of Doses Administered
Existing language would need to be modified
Formula is: Wastage factor = ((B + C) x D)/ A
Where :
A = the number of doses administered
B = the number of vials opened for use
C = the number of closed vials discarded due to cold chain failure or VVM
indication
D = the number of doses per vial
2. Using Stock Records
Again modify the existing language.
Formula would be : Wastage factor = ((B + C - D) x E)/A
Where :
A = the number of doses administered
B = the number of usable* vials in stock at the start of the year
C = the number of vials issued from the store for use
D = the number of usable* vials in stock at the end of the year
E = the number of doses per vial
This could then be followed by a simple conversion from wastage factor to
wastage rates, since people are still accustomed to report their wastage
rates.
* Vials of vaccine which are still permitted to be used.
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