Smallpox eradication in Brazil, 1967-69*

Bull. Org. mond. Sante 1970, 43. 797-808 Bull. Wld Hlth Org. | Smallpox Eradication in Brazil, 1967-69 * EURICO SUZART DE CARVALHO FILHO, M.D.,1 LEO MORRIS, M.P.H.,' ARLINDO LAVIGNE DE LEMOS, M.D., JUAN PONCE DE LEON, M.D.,4 ALBERTO ESCOBAR, M.D.5 & OSWALDO JOS1i DA SILVA, M.D.6 The Campanha de Erradicacao da Variola (CEV) was established in 1966 by the Brazilian Ministry of Health to eradicate smallpox. By October 1970 more than 75 mil- lion people had been vaccinated through this programme of systematic vaccination. In the 12 states where the attack phase had been completed by June 1969, there was an 80 % decrease in reported cases in 1969 compared with theprevious year. This decline in incidence contrasts sharply with the 99 % increase in cases recorded in the other 15 states due to the increased level of surveillance. In 1969, 74 % of cases occurred in persons under 15 years of age, while almost 93 % of the persons infected were less than 30 years ofage. The annual case-fatality rate, which has varied from 0.5 % to 3.3 % since 1956, indicates the disease to be variola minor. This has been confirmed by laboratory study. Careful investigation of reported cases has shown that in past years case reporting has been at a very low level, about 2.5 % of the actual incidence. Data from epidemiological investigations of 22 outbreaks comprising more than 2000 cases and contacts indicate that the efficacy ofsmallpox vaccination was approximately 94 %. The Brazilian Smallpox Eradication Programme- Campanha de Erradicagao da Variola (CEV)-was created on 31 August 1966 and was given the task of developing a nation-wide systematic vaccination campaign and of collecting, analysing, and dissemin- ating pertinent epidemiological information on small- pox in Brazil. Surveillance of the disease and evaluation of the coverage and effectiveness of the vaccination programme are continuing activities, and analyses of epidemiological data have been published since May 1967 in weekly surveillance reports. The present report summarizes the principal * From the Smallpox Eradication Programme (Campanha de Erradicaqao da Variola), Ministry of Health, Av. Beira Mar 216/803, Rio de Janeiro, Brazil. 1 Superintendent, Campanha de Erradicacao da Variola (CEV), 1968-69. 2 Pan American Health Organization Statistical Advisor to CEV, 1967-69; Present address: Epidemiology Program, Center for Disease Control, Atlanta, Ga. 30333, USA. 3Chief, Statistics Section, CEV, 1967-69. ' Pan American Health Organization Medical Advisor to CEV, 1967-69. ' Pan American Health Organization Medical Advisor to CEV, 1967-68; Present address: Departamento de Medi- cina Preventiva, Faculdade de Medicina, Bogoti, Colombia. ' Formerly Superintendent, CEV; Present address: Centro de Investigaq6es Epidemi6logicas, FSESP, Minist6rio da Sauide, Rio de Janeiro, Brazil. features of the Brazilian smallpox eradication pro- gramme in 1967, 1968 and 1969, and shows trends of the disease during this period. PAST OCCURRENCE OF SMALLPOX IN BRAZIL Although smallpox was first recorded in Brazil in 1563, outbreaks have been documented and de- scribed only since 1830 (Scorzelli, 1965). In this century, outbreaks were first recorded in 1904 and then in 1908 when over 9000 deaths were registered. In 1911, an estimated 250 000 cases occurred (Beau- repaire-Aragao, 1911). Historical data from one State, Guanabara, reveal a 3-6-year epidemic cycle since 1922 with a signifi- cant decrease in case-fatality ratios beginning in 1927 (Thibau, 1959). Sao Paulo has experienced 5-6-year epidemic cycles since 1950. During the past 25 years, nation-wide outbreaks occurred in 1944-45, 1955-56 and 1959-62. The number of smallpox cases and deaths reported for the period from 1956 to 1969 is presented in Table 1. Incidence rates, calculated from the estimated population in areas from which reports were received, better reflect the long-term trend in 2601 -797- 3 798 E. S. DE CARVALHO FILHO AND OTHERS TABLE I REPORTED SMALLPOX CASES AND DEATHS IN BRAZIL, 1958-80 Year 1 Population | No. of cases Incidencerate No. of deaths Case-fatality 4rate 1956 28 646 000 4 718 17.7 55 1.2 1957 27 313000 2651 9.7 36 1.4 1958 30 694000 2190 7.1 72 3.3 1959 29 467000 4 840 16.4 93 1.9 1960 45 371 000 6581 14.5 173 2.6 1961 67 952 000 8526 12.5 143 1.7 1962 73 087000 9 763 13.4 165 1.7 1963 76409000 6467 8.5 163 2.5 1964 76 211 000 3168 4.2 69 2.2 1965 78 587 000 3 417 4.3 45 1.3 1966 77 492 000 3623 4.7 29 0.8 1967 86 580 000 4 514 5.2 70 1.6 1968 89 376000 4 372 4.9 38 0.9 1969 92 282000 7 407 8.0 37 0.5 a Estimated population of areas covered by notification system (see text). b Per 100 000 estimated population. Brazil, since before 1961 cases were reported only from the state capitals and areas of the interior covered by FSESP (Fundacao Servi9o Especial de Saide Pfiblica) rural health units in 12 ofthe 21 states. Following the 1955-56 epidemic, a low point in incidence was reached in 1958 followed by another epidemic period that lasted from 1959 until 1962. Another low point in incidence occurred in 1964 followed by slight increases in each of the next 3 years. In 1969, the abrupt increase in reported cases of smallpox coincided with an intensified programme to improve the reporting system and surveillance in the more populous states. VACCINATION PROGRAMME A special programme of systematic vaccination was launched in the north-east region in 1962. Sub- sequently, in the latter part of 1966, the eradication programme expanded and intensified under the newly created CEV. In 1967, vaccination pro- grammes continued in the north-east region and were also started in the Federal District (Brasilia) and the States of Goias and Rio de Janeiro. As the systematic vaccination programme was completed in the north- eastern states, field operations were progressively extended to the more populous south-eastern and southern states. In the period from 1962 to 1966, a total of 6.4 million vaccinations was registered (Table 2). In 1967, the first full year of CEV's operation, 6.6 million vaccinations were given. This total was almost doubled in 1968, and in 1969 almost 21 million persons were vaccinated-an increase of 71 % over the number of persons vaccinated in 1968. The aver- age number of vaccinations administered weekly1 during 1969 was 394 093 and this average rose to 610 513 vaccinations each week during the final 11 weeks of the year (Fig. 1). By the end of 1969, a total of46 144 349 persons half the estimated Brazilian population-had been registered as vaccinated in the systematic vaccination programme. The programme had been completed in 8 of the 9 states of the north-eastern region, as well as the States of Espfrito Santo, Rio de Janeiro, Goias, and the Federal District. In January 1970, vaccination programmes were in progress in Bahia, Minas Gerais, Sao Paulo, Parana, and Rio Grande do Sul, and residents of most of the more densely populated urban areas had been vaccinated (Fig. 2). Vaccination programmes are scheduled to be con- ducted in Santa Catarina and Mato Grosso in 1970, and in the northern region (Amazonia) in 1971.2 1 For the statistical calculations of the Smallpox Eradi- cation Programme, 1969 was considered as a 53-week year. ' After this article had been set in print, it became known that up to October 1970, an additional 29 million vaccina- tions had been given, bringing the cumulative total of vac- cinations, since the start of the programme, to 75 069 871. The attack phase had been completed in all states with the exception of Rio Grande do Sul, Mato Grosso and the states of the northern region (Amazonia). SMALLPOX ERADICATION IN BRAZIL, 1967-69 NUMBER OF VACCINATIONS RECORDED TABLE 2 IN THE SYSTEMATIC VACCINATION PROGRAMME BY STATE AND YEAR, 196246,1967,1968 AND 1969 Estimated No. of vaccinations recordedRegion and state population a 1962- 197 1968 1969 Total North-east MaranAhob 3 615 000 c - - 1 106 633 1 186 059 2 292 692 Piauib 1 438 000 980 044 326 170 - - 1 306 214 Ceara b 3 914 000 - 2 528 610 1 180 433 - 3 709 043 Rio Grande do Norte b 1 312 000 954 812 - - - 954 812 Paralba b 2 287 000 - 1 525 083 794 501 - 2 319 584 Pernambuco b 4 817 000 3 837 202 - - - 3 837 202 Alagoas b 1 420 000 - 1 263293 - - 1 263 293 Fernando de Noronhab 2 000 _ - 1 240 - 1 240 Serglpe b 864 000 665776 - - - 665 776 Bahia 7 054 000 _ - 1 355 157 2 193 609 3 548 766 South-east Minas Gerals b 11 735 000 _ - 995 926 5 241 195 6 237 121 Espirito Santo b 1 537 000 _- - 1 455 393 1 455 393 Rio de Janeiro b 4 678 000 - 69 698 3 483 458 396 595 3 949 751 Sao Paulo 17186 000 - - 1 693 341 5 943 675 7 637 016 South ParanA 7 723 000 _ - - 3 338199 3 338 199 Rio Grande do Sul 6 728 000 - - - 1 132 218 1 132 218 West-central Golds b 2 865 000 - 507 878 1 613 237 2 121 115 Federal District b 410 000 - 374 914 - - 374 914 Total - 6 437 834 6 595 646 12 223 926 20 886 943 46144 349 a Mid-1969; Anuarlo Esfatistico Do BrasHl, Instituto Brasileiro De Estatistica, 1969. b Vaccination programme completed c CEV fleld records show that the population may have been overestimated as much as 30%. An assessment survey method was developed and field-tested in February 1968 and has been in opera- tion since April of that year (Lavigne & Morris, 1969). Two assessors visit each urban area and a sample of rural localities 7-14 days after completion of the vaccination campaign. In a random sample of households, vaccination coverage is ascertained for all residents, and primary vaccinees under 5 years of age are examined to determine the primary vaccina- tion take-rate. Primary take-rates have consistently been above 90%. Vaccination coverage has varied from 75% to 90% for children less than 5 years of age, from 90% to 100% for school-age children (5-14 years of age), and from 70% to 85% for persons 15-44 years of age. SURVEILLANCE PROGRAMME Sources of data The Epidemiology and Statistics Unit of CEV receives data from state and territorial health de- partments through a weekly reporting system. Basic data from this source have been supplemented by 799 E. S. DE CARVALHO FILHO AND OTHERS FIG. I ATTACK-PHASE VACCINATIONS BY QUARTER IN THE SMALLPOX ERADICATION CAMPAIGN IN BRAZIL I s aI I s2 4 i 3 1.S1. information received from other federal health agencies, diagnostic and research laboratories, and others with responsibility for and interest in smallpox control. At the beginning of the programme in 1966, there was no national morbidity reporting system in Brazil by which cases were reported regularly on a weekly basis. Reports were received on an irregular, often annual basis, and usually pertained to cases occurring in the state capitals only. As one of its first steps, a notification system was developed by CEV, and by the end of 1967, weekly morbidity reports were being received from 19 of the 27 " federation units " (22 states, 4 federal territories, and 1 federal district), while 6 other units submitted monthly reports. By the end of 1968, weekly reports were being sent by all but 4 federation units, and by the end of 1969, from all but 2, the States of Acre and Mato Grosso. Detailed data on cases of smallpox are collected on a national smallpox surveillance case record form. The preliminary report includes epidemiological information such as age, sex, residence, date of onset of illness, and outcome of illness. Beginning in 1968, a supplementary epidemiological form came into use which requested information regarding vaccina- tion history, contact history, information on travel within 3 weeks prior to onset of illness, laboratory information, and the age, sex, vaccination status, and smallpox history of all household contacts. The progressive improvement in the collection of basic epidemiological information is evident from Table 3. In 1966, annual reports included informa- 800 SMALLPOX ERADICATION IN BRAZIL, 1967-69 FIG. 2 STATUS OF THE SMALLPOX VACCINATION PROGRAMME IN BRAZIL, 31 DECEMBER 1969 SystematIc vaccination comploteq! Ssemtic9 vaccination programme In progress = Systematic vaccination to beoln In 1970 sSystematic vaccinaton to begin In 1071 TABLE 3 BASIC EPIDEMIOLOGIC INFORMATION RECEIVED ON REPORTED CASES, 1966-69 Cases with identifying data Total no. Daeo ne rmnh Total no. wtideathsin dtYear of cases Age and sex Date of onset or month of deaths with identifying data reported of report reported ____________ No. % No. % No. % 1966 3623 1547 42.7 3136 86.6 29 11 37.9 1967 4 514 2 561 56.7 4 438 98.3 70 29 41.4 1968 4 372 3 059 70.0 4 372 100.0 28 30 78.9 1969 7 407 6 795 91.7 7 407 100.0 37 37 100.0 801 802 E. S. DE CARVALHO FILHO AND OTHERS tion regarding age and sex of cases for less than half of those reported, and identifying data were available for only one-third of the deaths recorded. As the programme developed, the proportion of cases for which age and sex were known increased to 70% in 1968, and to 92% in 1969. By 1968, the date of onset or date of report was known for all notified cases; and by 1969, identifying data were available for all deaths. Surveillance activities The principal activity of CEV from 1966 to 1968 was field training and organization of the vaccina- tion programme. In 1969, a greater emphasis was placed on surveillance activities and epidemic inves- tigation. Physicians responsible for surveillance ac- tivities in the north-eastern region, GoiAs, Rio de Janeiro, Bahia, Minas Gerais, and ParanA were trained and assigned, and in late 1969, another surveillance-containment unit was established in Rio Grande do Sul. Their responsibilities included both the investigation of reported cases and outbreak control, and the further extension and development of the reporting network. The role of these containment operations in detect- ing additional cases of smallpox is well illustrated by the experience in Paran&. In that state, careful investigation of 16 reported cases from 15 different municipios uncovered 637 more cases, suggesting that, at best, 2.5% of cases were being reported. This represents much less complete reporting than has been observed in other countries. However, it should be noted that only variola minor infections are present in Brazil, and many persons are not sufficiently ill to require medical attention. This greater emphasis on surveillance and epidemic investigation contributed to a marked increase in the number of cases reported in 1969. However, it is important to note that this increase was confined to the States in which the vaccination campaign had not yet been completed or initiated, as shown below: Campaign status No. of No. ofcases reported 1969 States e 1969 1968 D(fference(%) Completed 12 146 715 -79.6 Not completed 15 7 261 3 657 +98.6 Total 27 7 407 4 372 +69.4 * Including the 4 territories and the Federal District. In the 12 states where the attack phase had been completed by June 1969, there was an 80% decrease in the number of cases reported compared with the previous year. This decrease contrasts sharply with the 99% increase in notified cases in the other 15 states in 1969.1 Seasonal and geographical distribution Fig. 3 shows reported smallpox cases, by 4-week periods, for 1967, 1968 and 1969. An early spring increase with peak incidence in September, October and November is seen each year, while the lowest incidence normally occurs between March and May. In 1969, both the seasonal increase and seasonal decline would appear to have occurred 4 weeks earlier than in previous years. This is believed to reflect a shorter period elapsing between onset of illness and the reporting of cases as a result of the intensification of surveillance and containment activities in March of that year. Smallpox was endemic in the whole of Brazil in the early 1960s. The average annual incidence for 1961- 65 ranged from 4.1 (per 100 000 population) in the northern region and Mato Grosso to 10.2 in the southern region (Table 4, Fig. 4). In 8 of the 9 north- eastern states where vaccination programmes have now been completed, annual case rates have pro- gressively declined from 5.3 per 100 000 in 1966 to 0.5 in 1969. In the States of Goias and Rio de Janeiro and in the Federal District, smallpox in- cidence in 1969 was 95% lower than the average annual rate recorded between 1961 and 1965. Although systematic vaccination programmes have not yet been initiated in the northern region or in Mato Grosso, a decline in smallpox is also seen there. State-sponsored programmes in Bel6m (Para) in 1964 (Silva, 1965) and Manaus (Amazonas) in 1967 pro- bably contributed to this decrease, as approximately 20% of the estimated population in this area live in one or other of the two capital cities. In the south-eastern and southern regions, small- pox has remained endemic in those areas not yet reached by the vaccination programme, The most severe urban outbreak of smallpox in 1967 occurred in the capital and surrounding municipios of S&o Paulo City. In 1968, severe outbreaks occurred in the interior of Ceara, Paraiba, Sao Paulo, GoiUs and Bahia. The largest outbreaks in the period 1967-69 occurred in 1969; over 500 cases were recorded in 1 After this article had been set in print, it became known that up to the week ending 28 November 1970, a total of 1769 cases of smallpox had been reported. This figure may be compared with the 6524 cases reported during the same period in 1969-a 73% decline in the number of cases. SMALLPOX ERADICATION IN BRAZIL, 1967-69 803 FIG.3 REPORTED SMALLPOX CASES IN BRAZIL BY 4-WEEK PERIOD DURING 196749 1,600 1,200 8 W1,000 Io 0 0600 400 200 0 WHO 0o661 1967 196s 19 TABLE 4 SMALLPOX INCIDENCE BY AREA IN BRAZIL: AVERAGE ANNUAL RATE FOR 196145 AND ANNUAL RATES FOR 1966-69 TEstimated Average Area populationmannual Annual Incidence a number Regions included (thousands) incldence a1969 1961465 IM96 1967 1968 1969 I North-eastern states with vaccination programme completed b 1966 5.8 5.3 2.6 1.6 0.5 2 Other states with vaccination programme completed c 7 953 10.0 7.2 6.2 5.5 0.5 3 Northern region b and Mato Grosso 4 842 4.1 2.3 1.3 1.3 0.8 4 South-eastern region b (excluding the State of Rio de Janeiro) and Bahla 42 577 8.8 5.1 7.0 6.8 12.7 5 Southern region b 17 241 10.2 2.6 4.3 4.7 10.6 a per 100000 population. b See Fig. 4 for states Included. Area no. 4 includes the State of Guanabara and the area comprised by Serra dos Almor6s although they are not shown on Fig. 4. c Goias, Rio de Janeiro, and the Federal District. E. S. DE CARVALHO FILHO AND OTHERS FIG. 4 MAP OF AREAS DEFINED IN TABLE 4 0 0 0 North-eastern states with vaccination programme completed Other states with programme completed Northern region and Mato Grosso O South-eastern region (excluding Rio de Janeiro) and Bahia O Southern region both Utinga (Bahia) and Uberaba (Minas Gerais). Extensive outbreaks also occurred throughout the interior of the State of Parana. Age and sex Information regarding the age and sex of cases is available for 70% and 92% of the cases reported in 1968 and 1969, respectively. In 1969, about 74% of these cases occurred in individuals under 15 years of age, and almost 93% in persons less than 30 years of age. The figures for 1968 were 69% and 88%, respectively (Table 5). Of the 247 cases in infants in 1969, 112 occurred in children younger than 6 months old, and 52 of these were less than 3 months of age. In 1968, approximately 60% of patients in the 1-4-year and 30-44-year age-groups were males but, in 1969, the differences in distribution by sex were not appreciable. Mortality Total deaths each year due to smallpox are shown in Table 1 and by age-group for 1968 and 1969 in Table 5. The case-fatality rate between 1956 and 1969 ranged from 0.5% to 3.3% (Table 1). In 1966, 1968, and 1969 the case-fatality rate was below 1.0%. While the over-all case-fatality rate was 0.9% and 0.5% in 1968 and 1969, respectively, it was 5.7% and 4.8% for infants less than 1 year old. The higher case-fatality rates in infants are due primarily to the 804 SMALLPOX ERADICATION IN BRAZIL, 1967-69 805 TABLE 5 REPORTED SMALLPOX CASES IN BRAZIL BY AGE-GROUP AND SEX IN 1968-69 Age-group ~No. of cases % of No. ofAge-group Male Female Total total deaths 1968 <1 72 68 140 4.6 8 1-4 436 308 744 24.3 7 5-14 630 582 1 212 39.6 3 15-29 308 298 606 19.8 7 30-44 130 78 208 6.8 3 >45 65 54 119 3.9 2 Not known 12 18 30 1.0 8 Total 1 653 1406 3059 100.0 38 1969 <1 125 122 247 3.6 12 1-4 800 778 1 578 23.2 10 5-14 1 581 1 596 3 177 46.8 5 15-29 639 646 1 285 19.0 8 30-44 166 142 308 4.5 0 >45 88 69 157 2.3 2 Not known 20 23 43 0.6 0 Total 3 419 3 376 6 795 100.0 37 very high rates observed in those less than 3 months of age. During 1968-69, 20 of the 387 patients less than 1 year old died (5.2 %), while among those less than 3 months old, 14 of 84 died (16.7 %). Five of the 14 deaths were in children less than 15 days old, indicating that variola infection took place at or shortly before birth. Vaccine efficacy An appraisal of the efficacy of smallpox vaccine was based on surveillance data from 22 outbreaks in Parani, Bahia, Minas Gerais, and Rio Grande do Sul. Smallpox cases were recorded in 351 households during the 22 epidemiological investigations. In the households there were 1799 contacts who had never suffered from smallpox. Of these contacts, 1376 were unvaccinated, and cases occurred in 1010 of them, giving an attack rate of 73.4%. Of the 423 contacts who had previously been successfully vaccinated, only 18 (4.3 Y.) contracted smallpox. The reduction in expected cases among the vaccinated was 94/o. DISCUSSION Since 1966, the geographical distribution of small- pox in Brazil has largely reflected the geographical coverage of the systematic vaccination programme. The progressive reduction of smallpox in vaccinated areas is evident in Table 4. However, the difference between vaccinated and nonvaccinated areas is even more vivid when seen graphically. In Fig. 3, which shows notifications for the whole of Brazil, the seasonal increase in the second half of the year is seen every year, as well as the significant increase in cases in 1969. In contrast, the number of reported cases in the north-eastern region (excluding Bahia, where the programme was still in progress in 1970), shows an abrupt drop in 1967, although the annual seasonal increase was still evident (Fig. 5). However, in 1968 and 1969, the incidence declined further and no significant seasonal increase was observed. In the States of Rio de Janeiro and Goias and in the Federal District, smallpox incidence decreased in 1968, although a seasonal increase occurred as in previous years (Fig. 6). However, in 1969, with the exception of 21 imported cases, indigenous smallpox had disappeared. The traditional spring increase in smallpox, with a peak incidence between September and November, corresponds to the dry season in most of Brazil. Before the eradication of smallpox in Venezuela, the cases there were concentrated in the first half of the year, which is their dry season." This association of peak smallpox incidence with the dry season is not limited to South America and has been also reported in Asia and Africa (National Communicable Disease Center, 1968). The majority of smallpox cases in Brazil have been in persons less than 15 years of age and as the proportion of cases that come to the attention of local health authorities is greater for adults than for children, smallpox is clearly a disease of the younger age-groups in Brazil. Low case-fatality rates, indicative of variola minor, did not always predominate in Brazil. Although variola minor, then described as alastrim, was first reported in 1910 in Bahia with subsequent spread to 1 Halbrohr, J. G. (1965) Caracteristicas epidemiologicas de la viruela (alastrim) en Venezuela durante el periodo 1935-1964. Paper presented at the Twelfth General Assembly of the Venezuelan Society of Public Health, Maracaibo. E. S. DE CARVALHO FILHO AND OTHERS FIG. 5 SMALLPOX CASES BY MONTH OF REPORT IN THE NORTH-EAST REGION OF BRAZIL DURING 1965-69a 400. 360 320 280 240-U) 0 200. D 160- 120 80. 40 . ATTACK PHASE -CEV\ I I t 965 1966 a Excluding the State of Bahia. FIG. 6 SMALLPOX CASES BY MONTH OF REPORT IN THE STATES OF RIO DE JANEIRO AND GOIAS AND THE FEDERAL DISTRICT OF BRAZIL DURING 1966-69 ATTACK PHASE - CEV ISO 1401 120 100o u 1 11 IMPORTED c Il CASES 806 SMALLPOX ERADICATION IN BRAZIL, 1967-69 807 SRo Paulo and other southern states (Ribas, 1910) case-fatality rates as high as 40% to 50% were still reported for some areas in the late 1920s (Thibau, 1959; Jorge, 1924). Since 1930, case-fatality rates in Brazil have been comparable with those seen in the USA from 1913 to 1933, which ranged from 0.3% to 2.2% (Hedrich, 1936). These epidemiological data, as well as laboratory studies, confirm that variola minor has been the only form of variola in Brazil in recent years (Downie et al., 1963; Bri9eno Rossi, 1963).1 The relatively high case-fatality rate seen in infants less than 3 months of age is to be particularly noted. Children from the time of birth should be eligible for vaccination in endemic areas since vaccination before the age of 3 months has been shown to be both safe and effective (Moodie & Cheeng, 1959; Lin, 1965; Lakhanpal, 1968). 1 Noble, J. & Salles-Gomes, L. F. (1968) A laboratory study of Brazilian smallpox. Paper presented at the Seminar on Laboratory Diagnosis of Smallpox in the Americas,, 9-13 September 1968, Instituto Oswaldo Cruz, Rio de Janeiro. R]ASUMt L'ERADICATION DE LA VARIOLE AU BRtSIL (1967-1969) La campagne bresilienne d'6radication de la variole a ete mise sur pied en ao(kt 1966. Ses objectifs 6taient de mener des op6rations de vaccination a l'6chelle natio- nale et de recueillir, analyser et diffuser toutes les infor- mations 6pidemiologiques relatives a la variole au Bresil. Entre 1962 et 1966, 6,4 millions de vaccinations ont et6 pratiqu6es dans les 6tats du nord-est, et en 1967, ann6e de plein d6veloppement du programme, 6,6 mil- lions. Les operations ont 6t6 progressivement 6tendues aux regions plus peupl6es du sud; 12,2 millions de personnes ont ete vaccin6es en 1968 et pres de 21 millions en 1969. A la fin de 1970, 75 millions de personnes avaient 6te immunis6es. Dans les 12 etats oiu la phase d'attaque etait arriv6e a son terme en juin 1969, on a note cette meme ann6e une diminution de 80% du nombre des cas notifiSs par rapport a 1968. Ce d6clin est i mettre en regard de l'augmentation de 99% du total des cas enregistr6s dans les 15 autres 6tats durant la meme periode, compte tenu des progres effectu6s en matiere de surveillance 6pid6miologique. Au Bresil, l'incidence de la variole presente un clocher annuel au printemps (septembre, octobre et novembre); la fr6quence de l'infection est minimale entre mars et mai. En 1969, 74% des cas ont ete observ6s chez des sujets ages de moins de 15 ans, et 93% au-dessous de 30 ans. Depuis 1956, les taux de l6talit6 annuels fluctuent entre 0,5 et 3,3%, attestant que la maladie rev8t uniquement la forme de la variole mineure, comme le confirment les etudes de laboratoire. On a accord6 de plus en plus d'importance aux acti- vit6s de surveillance, ce qui explique en grande partie la forte hausse de l'incidence relev6e dans les regions oii la campagne de vaccination 6tait toujours en cours en 1969. Apres une enquete epid6miologique soigneuse, on est arriv6 a la conclusion que, dans les meilleures conditions, le nombre des cas notifi6s au cours des der- nieres ann6es ne repr6sentait guere que 2,5 % de l'inci- dence r6elle. D'apr6s des observations portant sur 22 6pidemies de variole au cours desquelles plus de 2000 personnes ont 6t6 exposees a l'infection, la vaccination antivariolique a confdr6 une protection de l'ordre de 94%. REFERENCES Beaurepaire-Aragao, H. de (1911) Mem. Inst. Osw. Cruz, 3, 3-39 Briceno Rossi, A. L. (1963) Bol Ofic. sanit. Panamer., 24, 419-423 Downie A. W., Dumbell, K. R., Ayrosa Galvao, P. A. & Zatz, I. (1963) Trop. geogr. Med., 15, 25-28 Hedrich, A. W.. (1936) Publ. Hlth Rep. (Wash.), 51, 363-392 Jorge, Ricardo (1924) Lancet, 2, p. 1317 and p. 1366 Lakhanpal, U. A. (1968) Indian J. med. Res., 56, 1034- 1039 Lavigne, A. & Morris, L. (1969) Rev. bras. Evtat., 30, 300-302 Lin, H. J. (1965) Bull. Wld Hlth Org., 33, 321 Moodie, A. S. & Cheng, G. K. K. (1959) Tubercle (Edinb.), 43, 155 National Communicable Disease Center (1968) Smallpox Eradication Program SEP Report, 2, No. 3, pp. 2-3 Ribas, E. (1910) Trans. roy. Soc. trop. Med. Hyg., 4, 224 Scorzelli, A., Jr (1965) Arch. de Hig. (Rio de J.), 21, 3-64 Silva, W. (1965) Arch. de Hig. (Rio de J.), 21, 141-164 Thibau, Jr (1959) Rev. bras. Med., 16, 503-308