WORLD HEALTH ORGANIZATION ORGANISATION MONDIALE DE LA SANTÉ EXPERT COMMITTEE ON YELLOW FEVER Entebbe, 9-15 March 1971
VIR/YF/71,12
ORIGINAL:
FRENCH
VACCINATION PROGRAMMES IN EMERGENCIES by Dr P. Brès V i r u s Diseases u n i t INÙtXED
17D y e l l o w f e v e r v a c c i n e has l o n g proved t o be s a t i s f a c t o r i l y e f f e c t i v e and s a f e f o r i n d i v i d u a l v a c c i n a t i o n , b u t when t h i s v a c c i n e was used i n t h e p a s t f o r mass v a c c i n a t i o n , d i f f i c u l t i e s were caused by t h e l a r g e number o f s t e r i l e s y r i n g e s and n e e d l e s needed, making h i g h speed v a c c i n a t i o n d u r i n g an e p i d e m i c i m p o s s i b l e . The development o f i n j e c t i o n equipment w i t h o u t n e e d l e s , o f t h e Ped-O-Jet t y p e , was a c o n s i d e r a b l e s t e p f o r w a r d f o r mass v a c c i n a t i o n c a r r i e d out by m o b i l e teams. T h i s equipment, u n f o r t u n a t e l y , i s e x p e n s i v e and d i f f i c u l t t o s e r v i c e , but t h e o u t l a y i s j u s t i f i e d by i t s p e r f o r m a n c e . Operation o f a v a c c i n a t i o n team
D u r i n g an e p i d e m i c a m o b i l e v a c c i n a t i o n team may be l i m i t e d t o two p e r s o n s . A technician i s r e s p o n s i b l e f o r r e h y d r a t i n g t h e v a c c i n e and f o r k e e p i n g t h e i n j e c t i o n equipment i n good working order. H i s a s s i s t a n t , who may be a^ d r i v e r , a d m i n i s t e r s t h e v a c c i n e w h i l e t h e t e c h n i c i a n i s r e h y d r a t i n g t h e next f l a s k . F o r c o n t i n u o u s o p e r a t i o n , t h e team w i l l need s p a r e equipment i n c a s e t h e r e i s a m e c h a n i c a l breakdown. The number o f v a c c i n a t i o n s p<»r hour w i l l depend on e f f i c i e n t crowd c o n t r o l and w i l l vary between 500 and 3000 w i t h a Ped-O-Jot. Vaccination strategy V a c c i n a t i o n appears t o have been s t a r t e d e i t h e r i n t h e a r e a s on t h e peripho.-y o f t h e focui; o r i n t h e f o c u s i t s e l f depending on t h e e p i d e m i c . E p i d e m i o l o g i c a l d a t a may i n d i c a t e w h i c h i s t h e b e t t e r method. R e s u l t s o f p r e v i o u s s e r o l o g i c a l sample s u r v e y s may a l s o j u s t ' f y r e s t r i c t i o n o f v a c c i n a t i o n t o c e r t a i n age groups. I n l a r g e towns, p r i o r i t y may have t o be gi-'on t o h e a l t h p e r s o n n e l , t h e p o l i c e , t h e army, t r a n s p o r t s e r v i c e s , c i v i l s e r v i c e , i n d u s t r y and s c i o o l s . The p o p u l a t i o n o f urban c e n t r e s on l i n e s o f communication c o n n e c t e d w i t h t h e focus w i l l & j S o need ^ to be v a c c i n a t e d . A s i n g l e v a c c i n a t i o n i s c o n s i d e r e d t o g i v e p r o t e c t i o n f o r a t l e a s \ 17 y e a r s and i t i s v e r y l i k e l y t h a t two v a c c i n a t i o n s w i l l g i v e l i f e - l o n g p r o t e c t i o n . A n t i b o d i t t - appear i n t h e c i r c u l a t i o n on t h e a v e r a g e 10 days a f t e r v a c c i n a t i o n , but t h e p r o t e c t i v e e f f e c t i s thought to d e v e l o p e a r l i e r . The undue h a s t e and o r g a n i z a t i o n a l m i s t a k e s i n e v i t a b l e when a p a n i c i s touched o f f by t n e p i d e m i c s h o u l d n o t l e a d t o n e g l e c t o f t h e p r e c a u t i o n s needed t o e n s u r e s a f e and e f f e c t i v e vaccination. E f f e c t i v e n e s s depends p r i m a r i l y on t h e maintenance o f t h e v a c c i n e i n good c o n d i t i o n durings t o r a g e and t r a n s p o r t . 17D v a c c i n e may be k e p t up t o s e v e r a l months a t a t e m p e r a t u r e n o t e x c e e d i n g +4°C. However, i t i s f r e q u e n t l y d i f f i c u l t t o a v o i d e x p o s i n g t h e v a c c i n e t o h i g h e r t e m p e r a t u r e s when a m o b i l e team must o p e r a t e i n h o t c l i m a t e s a t s e v e r a l days j o u r n e y from i t s base. A s e r i e s o f c o l d s t o r a g e u n i t s w i l l o f t e n have t o be o r g a n i z e d t o p r e v e n t t h e v a c c i n e from d e t e r i o r a t i n g . Any l o w e r i n g o f v a c c i n e potency s h o u l d be a v o i d e d , p a r t i c u l a r l y as a h i g h e r The Issue of this document does not constitute formal publication. It should not be reviewed, abstracted or quoted without the agreement of the World Health Organization. Authors alone are responsible for views expressed in signed articles. 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/71.12 page 2 dilution of the vacc i n e is used in mass vaccination (Penna 1956) thus lowering the safety margin below the 1000 LD50 minimum dose laid down in the WHO recommendations. 3 The effectiveness of the rehydrated suspension also depends on its homogeneity, on shielding it from ultra violet radiation and heat when in use in the injector and on the correc t penetration of the vaccine dose under the skin. These factors are dependent on the personal qualities o f the vaccinator. As a rule, the vaccine is safe for subjects over six months of age. During mass vac c ina tion, especially in epidemics, insufficiently experienced technicians tend to neglec t asepsis when rehydrating the vac c ine. Sterility may also be overlooked when the inje c tor is di s mantled for unblocking. There should be a supervisor responsible for seeing that the personnel do not make this sort of mistake. Special risk of contamination by tetanus spores exists in savannah areas, where a great deal of dust is raised when crowds gather . Since the antigen substrate is composed of chick embryo proteins, allergic reactions to 17D vaccine may occur, generally appearing at once in sensitive subjects. Vaccinators should know how to deal with such accidents, which may be serious if anasarca or circulatory failure occurs. Evaluation of the effectiveness of the vaccination programme Pressure of events in an epidemic may lead to failure to follow up the effects of vaccination . A special team should conduct surveys of the vaccinated population to trace any local septic complications or neuro-meningeal reactions which may occur . A serological survey on a sample of the vaccinated population and on a random sample will enable vaccine potency and vaccination coverage to be evaluated. Many measures must of necessity be improvised during an epidemic. Nevertheless, it is essential to be prepared for immediate action so that valuable time is not lost in the first For this reason WHO has provided for the assembly of a permanently available stock few days. of two million vaccine doses and for a team ready to go into action i~ediately during the interval needed to get other teams together. 2
REFERENCES 1. 2. Groot , H. et al . (1962) Bull. Wld Hlth Org., ~,
699-707
World Health Organization (1956) Yellow Fever VaC Cination, Wld Hlth Org. Monogr. Ser., No. 30 World Health Organization (1959) Requirements for Biological Substances No. 3. Requirements for Yellow Fever Vaccine, Wld Hlth Org. techn . Rep. Ser., 179
3.