INOEXEO
WORLD HEALTH ORGANIZATION 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 1970
VIR/YF/70.2
ENGLISH ONLY
REGULAR VACCINATION PROGRAMMES IN "URBAN YELLOW FEVER" AREAS by A r t u r o C. Saenz M.D.
R e g u l a r s y s t e m a t i c v a c c i n a t i o n programmes i n towns and c i t i e s have n e v e r been u n d e r t a k e n i n t h e A m e r i c a s , a l t h o u g h mass v a c c i n a t i o n campaigns have been c a r r i e d o u t s p o r a d i c a l l y i n the t h r e a t o f e p i d e m i c s . The emphasis has been p l a c e d f r o m t h e b e g i n n i n g on t h e c o n t r o l and the e r a d i c a t i o n o f t h e urban v e c t o r t h e Aedes a e g y p t i . The s u c c e s s o f t h e Aedes a e g y p t i e r a d i c a t i o n campaigns i n l a r g e a r e a s o f t h e c o n t i n e n t h a s k e p t c i t i e s and towns, f r e e o f yellow fever i n t h i s part of the world. Y e l l o w f e v e r v a c c i n a t i o n was, and i s , c a r r i e d o u t i n p o p u l a t i o n s l i v i n g n e a r f o r e s t areas where the n a t u r a l c y c l e o f t h e v i r u s i s m a i n t a i n e d . In A f r i c a t h e c o n t r o l o f Aedes a e g y p t i i n urban a r e a s has n o t been s u c c e s s f u l because o f f r e q u e n t r e i n f e s t a t i o n from t h e n e i g h b o u r i n g f o r e s t s . I n t h e t e r r i t o r i e s under French a d m i n i s t r a t i o n mass v a c c i n a t i o n campaigns c o v e r i n g u r b a n and r u r a l p o p u l a t i o n s were i n i t i a t e d i n t h e e a r l y 40's and m a i n t a i n e d r e g u l a r l y up t o I960 when t h e y were abandoned o r reduced in the d i f f e r e n t c o u n t r i e s . More than 56 m i l l i o n v a c c i n a t i o n s had been c a r r i e d o u t by 1953, d o u b l e t h e number o f the p o p u l a t i o n o f those t e r r i t o r i e s a t t h a t t i m e . C i t i e s and towns as w e l l as t h e r u r a l departments were each d i v i d e d i n f o u r s e c t i o n s , t h e p o p u l a t i o n o f each s e c t i o n b e i n g vaccinated o r revaccinated r e g u l a r l y every f o u r t h year. D u r i n g t h i s p e r i o d no e p i d e m i c s were r e p o r t e d i n urban a r e a s a l t h o u g h s p o r a d i c c a s e s c o n t i n u e d t o o c c u r i n f o r e s t a r e a s . In 1965 a f t e r s e v e r a l y e a r s d u r i n g w h i c h no r e g u l a r mass v a c c i n a t i o n campaigns had t a k e n p l a c e an e p i d e m i c o c c u r r e d i n D i o u r b e l ( S e n e g a l ) , a f f e c t i n g m a i n l y c h i l d r e n u n d e r 10 y e a r s of age, t h e age group o f t h e p o p u l a t i o n n o t p r o t e c t e d . In t h e A f r i c a n t e r r i t o r i e s f o r m e r l y under B r i t i s h a d m i n i s t r a t i o n , no s y s t e m a t i c v a c c i n a t i o n campaigns were c a r r i e d o u t . When e p i d e m i c s o c c u r r e d i n N i g e r i a and Ghana i n 1969 l i t t l e d i f f e r e n c e was o b s e r v e d i n t h e d i s t r i b u t i o n o f c a s e s i n t h e d i f f e r e n t age g r o u p s . Recent e n t o m o l o g i c a l s u r v e y s show t h a t a m a j o r i t y o f c i t i e s , towns and v i l l a g e s i n West A f r i c a a r e d e n s l y p o p u l a t e d by Aedes a e g y p t i . As i t h a s been e s t i m a t e d t h a t t r a n s m i s s i o n of y e l l o w f e v e r can o c c u r when t h e Aedes a e g y p t i i n d e x i s more t h a n f i v e p e r c e n t . , t h e danger o f y e l l o w f e v e r e p i d e m i c s i n t h e s e a r e a s i s r e a l . As t h e c o n t r o l o f e r a d i c a t i o n o f Aedes a e g y p t i has been shown t o be e x t r a o r d i n a r i l y d i f f i c u l t o r i m p o s s i b l e i n A f r i c a t h e b e s t p r o t e c t i o n o f t h e p o p u l a t i o n a t r i s k can be o b t a i n e d by s y s t e m a t i c v a c c i n a t i o n . B e f o r e s t a r t i n g a mass v a c c i n a t i o n campaign i t i s a d v i s a b l e t o c a r r y o u t a s e r o l o g i c a l s u r v e y t o d e t e r m i n e t h e immunity due t o p r e v i o u s v a c c i n a t i o n o r n a t u r a l l y a c q u i r e d i n f e c t i o n of t h e d i f f e r e n t age groups o f t h e p o p u l a t i o n . However, under t h e t h r e a t o f an e p i d e m i c o r i f i t i s known t h a t no r e g u l a r v a c c i n a t i o n has been c a r r i e d o u t f o r many y e a r s i t may be The issue of this document does not constitute It should not bo reviewed, Authors alone Ce document ne constitue pas une publication.
formal 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.
abstracted or quoted without the agreement of the World Health Organization. articles. are responsible for views expressed in signed
V IRy'YF/70. 2 page 2 a d v i s a b l e t o p r o c e e d t o a mass v a c c i n a t i o n c a m p a i g n p r e l i m i n a r y survey. T h i s c a m p a i g n s h o u l d aim a t a c e p t i o n o f c h i l d r e n u n d f r s i x m o n t h s who s h o u l d n o t l o g i c a l s u r v e y has been c a r r i e d o u t t h e r e s u l t s of ol" t l i e p o p u l a t i o n s h o u l d be v a c c i n a t e d . w i t h 170 v a c c i n e w i t h o u t w a i t i n g f o r a hundred per c e n t , coverage w i t h t h e exbe v a c c i n a I f d . If a previous serot h i s survey w i l l i n d i c a t e which groups
A secont] s e r o l o g i c a l s u r v e y a f t e r t h i s v a c c i n a t i o n campaign w i l l g i v e a c c u r a t e inform a t i o n on t h e s u c c e s s o f t h e c a m p a i g n . The i m m u n i t y a f f o r d e d by v a c c i n a t i o n i s o f l o n g d u r a t i o n and p o s s i b l y f o r l i f e , t h e r e f o r e no r e v a c c i n a t i o n i s c o n s i d e r e d n e c e s s a r y unless i n t h e f a c e o f an e p i d e m i c , o r t h e t h r e a t o f an epidemic. Newcomers t o t h e p r e f e r a b l y not l o n g e r p o p u l a t i o n , by b i r t h o f i m m i g r a t i o n , than four or f i v e y e a r s . should be vaccinated at intervals '
The v e g e t a t i v e g r o w t h o f t h e p o p u l a t i o n i n m o s t o f A f r i c a i s c o n s i d e r e d t o be o f a b o u t two and a h a l f p e r c e n t , p e r y e a r . I f i n a d d i t i o n t o t h i s an i n c r e a s e o f t h e n o n - i m m u n e p o p u l a t i o n o f a b o u t one and a h a l f t o two p e r c e n t , a y e a r t a k e s p l a c e by i m m i g r a t i o n the p e r c e n t a g e o f n o n - i m m u n e may r i s e t o a b o u t 20 p e r c e n t , i n a p e r i o d o f f o u r t o f i v e years T h i s p e r c e n t a g e o f n o n - i m m u n e s i n t o w n s h e a v i l y i n f e s t e d w i t h AeOes a e g y p t i w i l l permit t h e t r a n s m i s s i o n o f t h e d i s e a s e and t h o d e v e l o p m e n t o f an e p i d f m i c . Immigrants f r e q u e n t l y concentrate i n s p e c i a l s e c t i o n s of c i t i e s s p e c i a l v a c c i n a t i o n campaigns at s h o r t e r i n t e r v a l s . w h i c h may require
S e r o l o g i c a l s u r v e y s s h o u l d be c a r r i e d o u t a t p e r i o d i c i n t e r v a l s o f a b o u t f i v e y e a r s t o o b t a i n i n f o r m a t i o n of the immunity l e v e l s of the d i f f e r e n t groups of the p o p u l a t i o n . P a r t i c u l a r l y i n t e r e s t i n g i s t h e age g r o u p f i v e t o s i x y e a r s o l d w h i c h i s e a s i l y a v a i l a b l e at school entrance. The k n o w l e d g e o f t h e i m m u n i t y l e v e l o f t h e p o p u l a t i o n w i l l facilitate d e c i s i o n s about the f o l l o w i n g v a c c i n a t i o n campaign. The a v a i l a b i l i t y o f j e t - i n j e c t o r s p e r m i t s t h e r a p i d v a c c i n a t i o n o f l a r g e n u m b e r s o f p e o p l e w i t h a r e l a t i v e l y s h o r t n u m b e r o f teams and p e r s o n n e l . T h i s method r e q u i r e s howeve the c o n c e n t r a t i o n of the p o p u l a t i o n at f i x e d v a c c i n a t i o n p o i n t s . This i s not difficult d u r i n g e p i d e m i c s b u t i t may n o t be s o e a s i l y o b t a i n e d f o r r e g u l a r v a c c i n a t i o n p r o g r a m m e s e s p e c i a l l y t h e y o u n g e r age g r o u p s . I t may be e a s i e r t o v a c c i n a t e c h i l d r e n i n m a t e r n a l and c h i l d o r i n p a e d i a t r i c s e r v i c e s where s u c h e x i s t . The d i f f i c u l t y h e r e i s t h a t a l a r g e m a j o r i t y o f t h e c h i l d p o p u l a t i o n h a s t o a t t e n d t h e s e s e r v i c e s i f a g o o d c o v e r a g e i s t o be obtained. The m e t h o d t o be a d o p t e d t o e n s u r e t h e i m m u n i z a t i o n o f t h o p o p u l a t i o n may v a r y i n d i f f e r e n t c o u n t r i e s o r a r e a s and r e c o m m e n d a t i o n s , v a l i d i n a l l c i r c u m s t a n c e s , c a n n o t be given. The p r o b l e m s h o u l d be c o n s i d e r e d by t h e l o c a l h e a l t h a u t h o r i t i e s and d e c i s i o n s t a k e n a c c o r d i n g t o t h e f a c i l i t i e s a v a i l a b l e and t h e h a b i t s o f t h e p o p u l a t i o n .