WORLD H E A L T H O R G A N I Z A T I O N ORGANISATION M O N D I A L E D E L A SANTÉ EXPERT COMMITTEE ON YELLOW FEVER E n t e b b e , 9-15 March 1971
VIR/YF/71.5 ORIGINAL; FRENCH
INDEX
VACCINES AND VACCINATION 17D AND DAKAR STRAIN VACCINES by
Dr Y. R o b i n , I n s t i t u t P a s t e u r , Dakar,
Senegal
Problems and d e s i r a b l e improvements: a d a p t a t i o n o f 17D v a c c i n e t o mass v a c c i n a t i o n campaigns; s t u d i e s on t h e r m o s t a b i l i t y ; q u a l i t y c o n t r o l ; s p e c i f i c recommendations t o t h e E x p e r t Committee on B i o l o g i c a l S t a n d a r d i z a t i o n (Dr Y, R o b i n ) . General The e s s e n t i a l r e q u i r e m e n t f o r any v a c c i n e i s t h a t i t s h o u l d be e f f e c t i v e and s a f e . The y e l l o w f e v e r v a c c i n e s , whether 17D o r Dakar s t r a i n , a r e c e r t a i n l y e f f e c t i v e . This was demonstrated most r e c e n t l y i n 1 9 6 5 ^ d u r i n g the e p i d e m i c a t D i o u r b e l , S e n e g a l , when o n l y n o n - v a c c i n a t e d c h i l d r e n were a f f e c t e d . No v a c c i n e can be c o m p l e t e l y h a r m l e s s s i n c e t h e i n t r o d u c t i o n o f an a n t i g e n i s i n i t s e l f an a t t a c k on t h e o r g a n i s m . However, t h e v i r u s s t r a i n employed and a l s o t h e s u b s t r a t e used t o p r o p a g a t e i t s h o u l d be s a f e . Both c h i c k s and mice a r e now known t o h a r b o u r l a t e n t v i r u s e s . Had t h i s been known when t h e s e v a c c i n e s were d e v e l o p e d , n e i t h e r o f them would have been approved, b u t f o r t u n a t e l y , they a r e a v a i l a b l e and no a d v e r s e e f f e c t o r o n c o g e n i c r e a c t i o n has y e t been a t t r i b u t e d t o a s u b s t r a t e c o n t a m i n a n t . However, i t would be w i s e t o t r y t o produce t h e s e v a c c i n e s on s u b s t r a t e s f r e e from p o t e n t i a l l y dangerous organisms even though the complete spectrum o f v i r u s c o n t a m i n a n t s remains unknown. The r e c e n t e p i d e m i c o u t b r e a k s i n A f r i c a d u r i n g 1969 l e d p u b l i c h e a l t h a d m i n i s t r a t i o n s i n the c o u n t r i e s concerned t o s e t up v a c c i n a t i o n programmes. Both 17D v a c c i n e and Dakar I n s t i t u t P a s t e u r s t r a i n v a c c i n e f o r s c a r i f i c a t i o n were used t o a p p r o x i m a t e l y t h e sam^^extent. Both v a c c i n e s o r i g i n a t e from r e s e a r c h c a r r i e d o u t by T h e i l e r and h i s c o l l e a g u e s . The v a c c i n e d e v e l o p e d a t t h e I n s t i t u t P a s t e u r , Dakar, came from a s t r a i n i s o l a t e d from a S y r i a n a t Dakar i n 1929 and s u b j e c t e d t o a s e r i e s o f passages on mouse b r a i n . The v a c c i n e i s a d m i n i s t e r e d by s c a r i f i c a t i o n and has been w i d e l y used i n A f r i c a , e i t h e r a l o n e o r i n combination with smallpox vaccine. Since t h e r e i s a r i s k o f e n c e p h a l i t i s i n c h i l d r e n , the v a c c i n e i s no l o n g e r used f o r s u b j e c t s under 10 y e a r s o f age. 17D v a c c i n e i s p r e p a r e d from a s t r a i n a t t e n u a t e d by passages on c h i c k - e m b r y o t i s s u e and i s i n t r o d u c e d by i n j e c t i o n . T h i s i s t h e v a c c i n e used f o r c h i l d r e n and, i n g e n e r a l , i n a l l primary v a c c i n a t i o n s . O c c a s i o n a l l y , however, i t may cause b e n i g n e n c e p h a l i t i s i n i n f a n t s .
The issue of this document does not constitute formal publication. It should not i>e reviewed, Authors alone abstracted or quoted without the agreement of the World Health Organization. articles. are responsible for views expressed in signed
Ce
document ne constitue pas une publication.
Il ne doit faire L'objet d'aucun compte rendu ou résumé ni d'aucune citation sans l'autorisation de l'Organisation Mondiale de la Santé. Les opinions exprimées dans les articles signés n'engagent que leurs auteurs.
VIR/YF/71.5
page 2 There has been l i t t l e change i n t h e p r e p a r a t i o n and a d m i n i s t r a t i o n o f b o t h v a c c i n e s since p u b l i c a t i o n o f t h e WHO monograph on t h e s u b j e c t i n 1956. N e v e r t h e l e s s , some c h a n g e s m i g h t be made n o t o n l y i n t h e p r e p a r a t i o n o f t h e s e v a c c i n e s but a l s o i n t h e i r c o n t r o l and a d m i n i s t r a t i o n The advantages and d i s a d v a n t a g e s o f each v a c c i n e , p a r t i c u l a r l y from t h e p o i n t o f v i e w o f mass v a c c i n a t i o n i n t r o p i c a l c o u n t r i e s , w i l l be examined below, and p o s s i b l e i m p r o v e m e n t s indicated. The r e p o r t w i l l c o n c l u d e w i t h some recommendations on t h e r e q u i r e m e n t s f o r y e l l o w f e v e r v a c c i n e , f o r p o s s i b l e s u b m i s s i o n t o t h e E x p e r t Committee on B i o l o g i c a l S t a n d a r d i z a t i o n . Dakar s t r a i n Substrate C l e a r l y " t h e s a f e t y o f t h e t i s s u e used f o r v i r u s growth i s as i m p o r t a n t as t h e s a f e t y o f the v i r u s i t s e l f " . ^ Dakar s t r a i n y e l l o w f e v e r v a c c i n e i s p r e p a r e d on mouse b r a i n s . After s e v e r a l m i l l i o n v a c c i n a t i o n s , no a c c i d e n t has as y e t been a t t r i b u t e d t o any mouse v i r u s contaminant ( i n p a r t i c u l a r , lymphocytic c h o r i o m e n i n g i t i s ) . However, i t would seem w i s e i n t h e f u t u r e t o s h i f t p r e p a r a t i o n o f t h i s v a c c i n e t o a n i m a l s f r e e from p a t h o g e n i c v i r u s e s . Do s u c h a n i m a l s e x i s t ? I t i s , i n f a c t , extremely l i k e l y t h a t a l a r g e number o f agents have n o t y e t been found s i n c e means o f d e t e c t i n g them have s t i l l t o be developed. Seed v i r u s The seed v i r u s i s t h e F r e n c h s t r a i n adapted by T h e i l e r t o w h i t e mice and known as F r e n c h N e u r o t r o p i c V i r u s (FNV). C u r r e n t p r a c t i c e i s t o use v i r u s seed l o t s a t t h e 260 passap;e l e v e l . T h i s v a c c i n e has e x c e p t i o n a l l y h i g h i m m u n i z i n g p r o p e r t i e s , i s r e l a t i v e l y t h e r m o s t a b l e , and i s r e a d i l y a p p l i c a b l e t o mass v a c c i n a t i o n a t r e a s o n a b l e c o s t . I t has , u n f o r t u n a t e l y , a s i g n i f i c a n t n e u r o t r o p i c e f f e c t . Current research, u s i n g passages a t s u b - o p t i m a l t e m p e r a t u r e s , i s aimed a t d e v e l o p i n g a c o l d v a r i a n t , w i t h a l t e r n a t e d n e u r o t r o p i c p r o p e r t i e s , b u t r e t a i n i n g a l l i t s immunogenic p o t e n c y . T h i s v a c c i n e s h o u l d c o n t i n u e t o be used i n i t s p r e s e n t form u n t i l such improvements h a v e been a c h i e v e d , p r o v i d e d t h a t i t i s r e s t r i c t e d t o a d u l t s i n c a s e s o f p r i m a r y v a c c i n a t i o n . it i s t h e v a c c i n e o f c h o i c e f o r r e v a c c i n a t i o n d u r i n g mass v a c c i n a t i o n campaigns. 17D vaccine Substrate I t i s known t h a t c h i c k e n s i n p o u l t r y farms may be c o n t a m i n a t e d by v a r i o u s a g e n t s s u c h a s i n f e c t i o u s l a r y n g o t r a c h e i t i s v i r u s (ILT), i n f e c t i o u s b r o n c h i t i s v i r u s (IBV), avian encephatom y e l i t i s v i r u s ( A E ) , a v i a n orphan v i r u s (GAL), chick-embryo l e t h a l orphan v i r u s (CELO), Y a c a p i a m y x o - v i r u s (YMV), f o w l pox v i r u s (FPV), N e w c a s t l e D i s e a s e v i r u s (NDV), Rous sarcoma v i r u s (RSV) and, i n p a r t i c u l a r , a v i a n l e u c o s i s v i r u s . S i n c e 17D v a c c i n e p r e p a r e d from c h i c k embryos p r o b a b l y c o n t a m i n a t e d by a v i a n l e u c o s i s v i r u s has been a d m i n i s t e r e d t o m i l l i o n s o f p e r s o n s w i t h o u t any c l i n i c a l , s t a t i s t i c a l o r e p i d e m i o l o g i c a l e v i d e n c e o f i n c r e a s e i n t h e i n c i d e n c e o f l e u k a e m i a , i t i s f a i r l y c l e a r t h a t t h e a v i a n l e u c o s i s complex has l i t t l e o r no o n c o g e n i c a c t i o n on man. I t i s , however, now p o s s i b l e t o use eggs from c o n t r o l l e d p o u l t r y b r e e d i n g c e r t i f i e d f r e e from a v i a n l e u c o s i s . establishments vaccine
VIR/YF/71.5
page Seed virus
3
A l l s e e d v i r u s e s u s e d a r e d e r i v e d f r o m t h e 17D s t r a i n o b t a i n e d by T h e i l e r and L l o y d o f t h e R o c k e f e l l e r F o u n d a t i o n , New Y o r k . However, the s e q u e n c e o f p a s s a g e s i s d i f f e r e n t i n e a c h c a s e and n e a r l y e v e r y p r o d u c i n g i n s t i t u t e h a s i t s own strain. S t a n d a r d i z a t i o n of world p r o d u c t i o n w o u l d be a d v i s a b l e and f o r t h i s p u r p o s e t h e b e s t s t r a i n among t h o s e i n c u r r e n t u s e s h o u l d be s e l e c t e d . There i s thus a need f o r a c o m p a r a t i v e s t u d y of the d i f f e r e n t s t r a i n s u s e d i n p r e p a r i n g primary seed l o t s . The n e e d t o s t a n d a r d i z e s e e d v i r u s w i l l become u r g e n t i f t h e r e q u i r e m e n t s f o r m e a s l e s v a c c i n e ® a r e t o be a p p l i e d t o 17D v a c c i n e . A l l s e e d l o t s u s e d a t p r e s e n t may i n p r a c t i c e be r e g a r d e d a s c o n t a m i n a t e d by a v i a n l e u c o s i s v i r u s . F u r t h e r m a n i p u l a t i o n of t h i s s t r a i n , i n p a r t i c u l a r by a d d i t i o n a l p a s s a g e s , ^ ' ^ ^ ^ w i l l be n e e d e d t o r i d s e e d l o t s o f t h i s c o n t a m i n a n t . I n a d d i t i o n t o the c o n t r o l s t e s t s s p e c i f i e d f o r normal seed l o t s , the immunogenic a c t i o n of t h i s s t r a i n o n man w i l l h a v e t o be c h e c k e d b e f o r e i t c a n be u s e d f o r p r o d u c i n g v a c c i n e . The s e l e c t e d s t r a i n s h o u l d t h e n be d i s t r i b u t e d t o a l l m a n u f a c t u r i n g l a b o r a t o r i e s a s p r i m a r y s e e d l o t s f r o m w h i c h t h e s e c o n d a r y s e e d l o t s n e e d e d t o m a n u f a c t u r e v a c c i n e w i l l be p r e p a r e d . C l e a r l y , t h e i d e a l s o l u t i o n w o u l d be f o r m a n u f a c t u r i n g l a b o r a t o r i e s t o r e c e i v e r e g u l a r c o n s i g n m e n t s of secondary seed l o t ampoules from which t o p r e p a r e t h e i r v a c c i n e d i r e c t l y . T h u s a s i n g l e l a b o r a t o r y w o u l d be r e s p o n s i b l e f o r s u p p l y i n g a l l o t h e r s w i t h s e c o n d a r y s e e d lots. Thermostability The cold low r e s i s t a n c e of u n i t s needed 17D vaccine t o h e a t and the difficulty vaccine of s e t t i n g up the series of
storage
i s the
major snag i n using
this
f o r mass v a c c i n a t i o n
campaigns i n t r o p i c a l
countries.
A n y a t t e m p t t o o b t a i n t h e r m o s t a b l e m u t a n t s f r o m t h e 17D p a r e n t s t r a i n i s c l e a r l y o u t o f the question. However, f r e e z e - d r y i n g t e c h n i q u e s g r e a t l y a f f e c t the r e l a t i v e t h e r m o s t a b i l i t y of a g i v e n p r e p a r a t i o n . A r e c e n t study-*-*^ o f t h e b e h a v i o u r a t d i f f e r e n t t e m p e r a t u r e s o f e i g h t v a c c i n e s from v a r i o u s s o u r c e s r e v e a l e d marked d i f f e r e n c e s : the behaviour of three preparations was v e r y g o o d , o f t h r e e o t h e r s g o o d and o f two o n l y f a i r . On a v e r a g i n g t h e r e s u l t s , h o w e v e r , a n i d e a c o u l d be f o r m e d o f t h e t h e r m o s t a b i l i t y o f 17D v i r u s . The m a i n p o i n t i s t h a t l y o p h i l i z e d 17D y e l l o w f e v e r v a c c i n e c a n k e e p a l m o s t a s w e l l a t +4°C a s a t -20°C. H o w e v e r , +4°C i s t h e t e m p e r a t u r e i n s i d e a d o m e s t i c r e f r i g e r a t o r and a l s o t h a t i n s i d e an i c e - f i l l e d isothermic c o n t a i n e r , w h i c h i s e a s i e r t o h a n d l e i n t h e t r o p i c s t h a n a f r e e z e r g i v i n g a t e m p e r a t u r e o f -20°C. The by so should as be above r e s u l t s , c a r r i e d out however, stem from p r e l i m i n a r y s t u d i e s o n l y i n t o the with degradation the highest of 17D vaccine by and should At by the be followed up tests
more d e t a i l e d r e s e a r c h to obtain
heat.
same t i m e , as a
to improve l y o p h i l i z a t i o n
conditions, in particular possible thermostability
using
protectors, reference
a preparation
to serve
vaccine. Filling and containers
WHO r e q u i r e m e n t s ^ at present s p e c i f y t h a t flame s e a l e d ampoules of h i g h q u a l i t y n e u t r a l g l a s s s h o u l d be u s e d f o r f i l l i n g . S i n c e t h e i n t r o d u c t i o n o f j e t i n o c u l a t i o n , w h i c h was first used i n m a s s m e a s l e s v a c c i n a t i o n c a m p a i g n s , t h e n e e d h a s b e e n f e l t f o r a p a c k i n g b e t t e r s u i t e d t o the i n s t r u m e n t , one t h a t w o u l d e l i m i n a t e t h e i n t e r m e d i a t e p r o c e s s e s o f s u s p e n d i n g and d i l u t i n g the v a c c i n e , which are d i f f i c u l t to c a r r y out i n the f i e l d , e s p e c i a l l y under s t e r i l e c o n d i t i o n s , and i n v o l v e t a k i n g a l i t t l e s o l v e n t f r o m t h e f l a s k , r e h y d r a t i n g t h e a m p o u l e and transferring the contents to the f l a s k , L y o p h i l i z a t i o n was t h e r e f o r e t r i e d o u t i n t h e f l a s k itself. The f l a s k was c l o s e d by a r u b b e r s t o p p e r k e p t i n p l a c e by a m e t a l c a p . Since s t o p p e r i n g was d o n e u n d e r v a c u u m , r e h y d r a t i o n was e x t r e m e l y s i m p l e . A double-ended needle ( v a c u t a i n e r t y p e ) was u s e d t o p i e r c e t h e s t o p p e r o f t h e s o l v e n t f l a s k , w h i c h was t h e n i n v e r t e d
VIR/YF/71.5
page 4 o v e r t h e v a c c i n e f l a s k and the l a t t e r ' s s t o p p e r p i e r c e d by the o t h e r end o f t h e n e e d l e . As t h e v a c c i n e f l a s k i s under vacuum, the s o l v e n t i s sucked d i r e c t l y i n t o i t . Since a l l procedures t a k e p l a c e i n a c l o s e d system t h e r e i s n e g l i g i b l e r i s k of c o n t a m i n a t i o n . T e s t s have c o n f i r m e d t h a t the at -20°C, and f o r a t l e a s t a month i n p r o c e s s s i n c e t h e r e i s no doubt v a c c i n a t i o n by j e t i n j e c t o r i n the Administration 17D 0.5 ml. y e l l o w f e v e r v a c c i n e i s a d m i n i s t e r e d by subcutaneous i n j e c t i o n ; the dose i s g e n e r a l l y vacuum i s m a i n t a i n e d f o r at l e a s t s i x months i n f l a s k s k e p t i n f l a s k s kept a t +4''C, +27°C and +37°C. Further tests are t h a t t h i s type of p a c k i n g marks a d e f i n i t e a d v a n c e f o r mass field in Africa.
A t t e m p t s have been made to check the e f f e c t i v e n e s s of i n t r a d e r m a l a d m i n i s t r a t i o n o f t h e vaccine.9 The r e s u l t s have been v e r y e n c o u r a g i n g . Other s t u d i e s , c a r r i e d o u t on a l a r g e r s c a l e but not y e t put i n t o p r a c t i c e , a l s o i n v o l v e i n t r a d e r m a l y e l l o w f e v e r v a c c i n a t i o n u s i n g a j e t i n j e c t o r and an i n t r a d e r m a l i n j e c t i o n n o z z l e d e l i v e r i n g 0.15 ml of v a c c i n e . This vaccine w i l l c l e a r l y have to s a t i s f y potency s t a n d a r d s , i . e . each v a c c i n e dose s h o u l d c o n t a i n a t l e a s t 1000 L D 50. The i n c o r p o r a t i o n of y e l l o w f e v e r v a c c i n a t i o n i n the mass v a c c i n a t i o n campaigns a t p r e s e n t under way i n A f r i c a g i v e s i n c r e a s i n g urgency to r e s e a r c h i n t o v a c c i n e c o m b i n a t i o n s . A m e a s l e s - s m a l l p o x - y e l l o w f e v e r c o m b i n a t i o n has been t r i e d . ^ A l t h o u g h good r e s u l t s were o b t a i n e d f o r measles and s m a l l p o x , o n l y 70-85 per c e n t , o f s u b j e c t showed s e r o l o g i c a l c o n v e r s i o n f o r yellow fever. T h i s t e s t s h o u l d be r e p e a t e d w i t h d i f f e r i n g a n t i g e n c o n c e n t r a t i o n s . E x p e r i m e n t s were c a r r i e d out on i n t r a d e r m a l a d m i n i s t r a t i o n of a B C G - y e l l o w f e v e r c o m b i n a t i o n by j e t i n j e c t o r ( P e d - O - J e t ) . ^ R e s u l t s were v e r y s a t i s f a c t o r y w i t h a good to b o t h v a c c i n e s , n e i t h e r of which was a f f e c t e d by the presence of the o t h e r . S p e c i f i c recommendations to the E x p e r t Committee on B i o l o g i c a l S t a n d a r d i z a t i o n In view o f t h e work done and p r o v i d e d t h a t t e s t s c u r r e n t l y under way c o n f i r m i n i t i a l r e s u l t s , the f o l l o w i n g amendments t o the r e q u i r e m e n t s f o r y e l l o w f e v e r v a c c i n e a r e p r o p o s e d . ^ P a r t A, s e c t i o n 4: f i l l i n g and containers
response
P a c k i n g the f i n a l v a c c i n e i n f l a m e s e a l e d ampoules s h o u l d no l o n g e r be mandatory. I t should be s u f f i c i e n t t o a p p l y the p r o v i s i o n s o f p a r t A, s e c t i o n 4, of the 1965 R e v i s i o n of t h e R e q u i r e ments f o r B i o l o g i c a l Substances No. 1 ( G e n e r a l Requirements f o r M a n u f a c t u r i n g E s t a b l i s h m e n t s and C o n t r o l Laboratories)® w h i c h s a y s : " C l o s u r e s s h a l l be of m a t e r i a l t h a t does n o t have d e l e t e r i o u s e f f e c t on the b i o l o g i c a l s u b s t a n c e s and s h a l l be d e s i g n e d t o m a i n t a i n a h e r m e t i c s e a l t h r o u g h o u t the d a t i n g p e r i o d " . P a r t A, s e c t i o n 8: labelling
P r e s e n t r e q u i r e m e n t s ^ s p e c i f y t h a t the f o l l o w i n g i n f o r m a t i o n , among o t h e r s , be i n d i c a t e d : "the volume of the recommended i n d i v i d u a l dose and the mode of a d m i n i s t r a t i o n ( s u b c u t a n e o u s injection)". The p a r e n t h e s i s s h o u l d be d e l e t e d . Conclusions J e t i n j e c t o r s have made 1 7 D y e l l o w f e v e r v a c c i n e a v a i l a b l e f o r mass v a c c i n a t i o n c a m p a i g n s . Recent s t u d i e s have shown t h a t the d r i e d v a c c i n e keeps w e l l a t +4°C, i . e . a t the t e m p e r a t u r e i n s i d e a h o u s e h o l d r e f r i g e r a t o r o r an i c e - f i l l e d i s o t h e r m i c c o n t a i n e r . However, the c o n s t i t u t e d v a c c i n e has t o be p r e p a r e d on the s p o t and used w i t h i n the n e x t h o u r , and, under p r e s e n t p a c k i n g
VIR/YF/71.5
page 5 conditions, i n the f i e l d s t o p p e r held substantial p r e p a r a t i o n i n v o l v e s a c e r t a i n number of p r o c e d u r e s t h a t are d i f f i c u l t to c a r r y out under a s e p t i c c o n d i t i o n s . P a c k i n g i n f l a s k s s e a l e d under vacuum u s i n g a rubber down w i t h a metal cap, g r e a t l y s i m p l i f i e s the o p e r a t i o n and a f f o r d s a very guarantee of s t e r i l i t y .
REFERENCES 1. Chambon, L, et a l . (1967) humaine, B u l l . Wld Une épidémie de fièvre j a u n e H l t h Org, , 36_, 113-150 fever vaccine f r e e from au Sénégal en 1965, L'épidémie
2.
D r a p e r , C, C. (1967) A yellow ( L o n d , ) , 65, 505-513
avian
leucosis viruses,
J . Hyg.
3.
Meyer, H. M. et a l . (1964) Response o f V o l t a c h i l d r e n t o j e t i n o c u l a t i o n o f combined l i v e measles, s m a l l p o x and y e l l o w f e v e r v a c c i n e s . B u l l . Wld H l t h Org., 30, 783-894 Wld H l t h Org. (1956) S e r i e s , No. 30 Y e l l o w Fever V a c c i n a t i o n , Geneva. Wld H l t h Org., Monograph
4.
5.
Wld
H l t h Org. (1959) Requirements f o r B i o l o g i c a l S u b s t a n c e s No, yellow fever vaccine. Wld H l t h Org., t e c h n . Rep. S e r . , 179, H l t h Org. (1966a) Rep. Ser., 323 H l t h Org. Ser., 325 (1966c) Wld Requirements f o r measles v a c c i n e H l t h Org., t e c h n . Rep. Ser., 329 (1966b) Requirements f o r B i o l o g i c a l Substances.
3, Requirements f o r 13-32 Wld H l t h Org., techn.
6.
Wld
7.
Wld
Human V i r a l
and
R i c k e t t s i a l Vaccines.
Wld
H l t h Org.,
techn.
Rep.
8.
Wld
H l t h Org.
( l i v e ) and (Annex 2)
measles
vaccine
(inactivated). 9.
R o b i n , Y. et a l . V a c c i n a t i o n a n t i a m a r i l e s i m p l e ou associée à l ' a i d e du v a c c i n 17D administré par v o i e i n t r a d e r m i q u e . OCCGE, Rapport f i n a l de l a lOème Conférence T e c h n i q u e , B o b o - D i o u l a s s o , 20-24 A v r i l 1970, 273-281 R o b i n , Y. et a l . (1971) Etude de l a thermostabilité du v a c c i n a n t i a m a r i l s u r des échantillons de h u i t l o t s p r o v e n a n t de d i v e r s p a y s . B u l l . Wld H l t h Org., à paraître T a u r a s o , N. M. e t a l . (1969) Yellow fever vaccine. I I . of a v a c c i n e seed f r e e from a v i a n l e u c o s i s v i r u s . T a u r a s o , N. M. e t a l . ( 1 9 6 8 ) Yellow fever vaccine. f r e e from c o n t a m i n a t i n g a v i a n l e u c o s i s v i r u s e s . 1116-1120 T h e i l e r , M. (1951) i n S t r o d e , G. K., ed. A n t i g e n i c i t y and neurovirulence A p p l . M i c r o b i o l . , 17, 866-870 seed 127,
10.
U .
12.
I , Development of a v a c c i n e P r o c . Soc, E x p t l , B i o l , Med.,
13.
Yellow f e v e r .
M c G r a w - H i l l , New
York, p.39