Epidemiological data on Hong Kong influenza in France

402 DISCUSSION PAPERS-SESSION I TABLE 3 Hi TITRES OF VIRUSES ISOLATED AT THE NATIONAL INFLUENZA CENTRE, BANGKOK, 1968 Titre to the following hyperimmune ferret antisera irusisolated-A2/Singapore/ A2/England/ A2/Tokyo/ A2/Hong Kong/ 1/57 12/64 3/67 1/68 A2/Singapore/1/57 >2 560 240 80 160 A2/England/12/64 480 >2 560 64 80 A2/Tokyo/3/67 <20 30 160 <20 A2/Hong Kong/1/68 80 <20 <20 1 920 A2/Bangkok/2/68 60 <20 <20 1 920 rise in HI antibody titre was demonstrated in 52 cases. Based on inquiries made to 6630 families (1.7% of the total population) in Bangkok, the attack rate was estimated to be 47 per thousand and the total number of patients in this city was approximately 150000. However, since the influenza during this outbreak was mild and since analysis was based on clinical diagnosis only, the extent of the outbreak may have been underestimated. Epidemiological Data on Hong Kong Influenza in France by R. SOHIER a & M. HENRY b Hong Kong influenza was first observed in France in the last 2 weeks of January 1969, when sporadic cases occurred in the district of Paris, and developed progressively throughout the country. The peak was reached in March, the incidence began to decrease in April, and the last cases were observed in May. The incidence remained relatively low and the ex- tent moderate, and the disease was mild or of moder- ate severity. In many parts of the country, only spo- radic cases were observed. Some local outbreaks were reported in towns or villages. Generally, influ- enza (confirmed by virus isolation or by serological tests) was observed in all age-groups, but in some outbreaks the greatest incidence occurred in children aged 4 years or less; in other outbreaks it occurred among those aged 15-24 years. The disease occurred less frequently among the older age-groups. a Virology Department, National Public Health Labora- tory, Lyon, France. b Faculty of Medicine. University of Lyon, France. It was difficult to obtain comprehensive mortality data, since notification of influenza is not compulsory in France, but deaths from clinically diagnosed cases were reported by some practitioners. Data on such reported cases are collected every year in roughly the same manner, and the figures for the first 4 months of 1967, 1968, and 1969 can be compared. During thlIse past years, all but one of the influenza A2 outbreaks occurred in a period extending from January to April, with a peak in February-March, as we have been able to show by means of a conti- nuous survey performed by CF tests using soluble (nucleocapsidic) type-specific antigen. As shown in the accompanying figure, the number of deaths from influenza during the first 4 months of 1969 was 3186, less than the number for the comparable periods of 1968 and 1967 (7267 and 3472, respectively). The first positive CF test appeared in the course of our continuous surveillance some weeks before the 2381D EPIDEMIOLOGICAL DATA ON HONG KONG INFLUENZA IN FRANCE 403 TABLE I HAEMAGGLUTINATION-INHIBITING ANTIBODIES AGAINST INFLUENZA A2/Hong Kong/68 IN SERA COLLECTED BEFORE THE OUTBREAK OF HONG KONG INFLUENZA No. of sera showing the following Hi Proportion of sera Age No. antibody titres: showing HI(years) of sera antibody titre 1 10 20 [40 80 |160 320 Fraction _% 0-10 29 3 3 2 8/29 27 11-20 33 3 3 1 1 8/33 24 21-30 23 2 2 4/23 17 31-40 27 1 1 1 1 4/27 14 41-50 31 2 2 4 2 10/31 32 51-60 24 1 1 1 1 4/24 16 61-70 38 4 2 1 . I 1 9/38 23 71-88 5 1 3 4/5 Total ] 210 }17 [14 9 4 2 5 51/210 24 INFLUENZA MORTALITY IN FRANCE DURING THE FIRST FOUR MONTHS OF 1967, 1968, AND 1989 3344 2802 1459 911 802 672 545 300 1961 flU 19-61 -80 1967 68-09 1961-66-69 JANUARY FEBRUARY MARCH APRIL WHO 916391 first isolation. Viruses similar to the A2/Hong Kong/ 68 virus were isolated in primary monkey kidney cultures and in embryonated eggs, but in the latter the isolation was accomplished more easily than during epidemics that occurred in recent years. In order to explain the marked differences from country to country in the intensity and impact of Hong Kong influenza, and particularly the low incidence and the mildness of the disease in France, we undertook some serological studies using haemagglutination-inhibition and neutralization tests. The results are summarized in Tables 1 and 2. Table 1 shows that haemagglutination-inhibiting antibodies to the A2/Hong Kong/68 virus were present in 51 (24 %) of210 sera collected from persons in different age-groups more than 4 months before the outbreak. However, these results have yet to be confirmed.c Table 2 shows that HI antibodies were present in 33 of 49 sera, and neutralizing antibodies in c A co-operative study is now being undertaken by the WHO World Influenza Centre, London, England, the International Influenza Center for the Americas, Atlanta, Ga., USA, and the National Influenza Centre, Lyon, France, to compare the results obtained in different labora- tories and to obtain information on the presence or absence of antibodies to the A2/Hong Kong/68 influenza virus before the occurrence of outbreaks. 404 DISCUSSION PAPERS-SESSION I TABLE 2 HAEMAGGLUTINATION-INHIBITING ANTIBODIES AND NEUTRALIZING ANTIBODIES AGAINST INFLUENZA A2/Hong Kong/1/68 IN OLD PEOPLE BEFORE AND AFTER VACCINATION WITH INACTIVATED VACCINE PREPARED WITH INFLUENZA A2/Netherlands/65 AND B/Netherlands/66 I ~~~~~~~~~~~No.of prevaccinatlon T No. of post-vaccination sera showing: | sera showing the followingTest Virus No. rises in antibody titre: I~ ~~~~~ofcssAntibodies IAntibodiesINoe 2fl I>4od l opresent Inot present None | Haemagglutination inhibition A2/Hong Kong!1/68 49 33 16 21 18 10 A2/Singapore/4/57 16 5 11 4 5 9 Neutralization A2/Hong Kong/1/68 16 10 6 6 5 5 A/Equi-2/France/3/65 13 5 8 13 0 0 10 of 16 sera obtained from old people. Vaccination with an inactivated virus vaccine prepared from A2/Netherlands/65 and B/Netherlands/66 viruses induced an increase of antibodies against the A2/Hong Kong/68 virus (a 4-fold or greater rise in HI antibodies was found in 10 of 49 sera, and a similar rise in neutralizing antibodies was found in 5 of 16 sera). No case of A2/Hong Kong influenza occurred in this group. In spite of these observations, the discrepancies in epidemic prevalence in different countries remain unexplained. Experience with A2/Hong Kong Influenza Infections in US Military Personnel* by ROBERT 0. PECKINPAUGH, MAX J. ROSENBAUM & EARL A. EDWARDS The first sizeable outbreak of Hong Kong influ- enza in the USA occurred among marines at the Drill Instructor School, San Diego, Calif. during 2-6 September 1968.a Clinical data and specimens were collected by US Navy Preventive Medicine Unit No. 5. Of a group of 49 marines 22 reported mild symptoms of acute respiratory disease. Only 3 were febrile and none required hospitalization. All symptoms disappeared within 24-48 hours after the onset of illness. Nine strains of the Hong Kong influenza virus were isolated from 22 throat swab specimens. The antigenic relationship of 1 isolate (San Diego/249) * From Naval Medical Research Unit No. 4, Great Lakes, Ill., USA. a Morbidity and Mortality Weekly Report 1968, 17, 357. to other strains of influenza A2 virus is shown in Table 1. The data indicate that there has been considerable antigenic drift away from the 1957 strain (A2/Japan/305/57) during the past 11 years. The 1967 strain (A2/Ann Arbor/67) seems to occupy an intermediate position between those strains iso- lated prior to 1967 and the recent Hong Kong variety. However, these data do not suggest that the Hong Kong strain is sufficiently different from the antecedent strains to warrant its reclassification as a new subtype (A3). Table 2 shows the results of haemagglutination- inhibition (HI) tests on paired, acute and convalescent sera from 16 patients involved in the San Diego outbreak and in a later occurrence (26-30 September) of influenza-like disease in sailors aboard the air- craft carrier USS Kitty Hawk. Several strains of 2381E