poliovirus during the three months in 1963 were very markedly less than in previous year. Other enterovirus excretion rates were also lower.
240. Three serological surveys for polio-antibodies were carried out. The first, in April, 1963 was on sera obtained in Maternal and Child Health Centres from children aged 6-12 months who had received two doses of gral Sabin trivalent vaccine. Presence of antibodies was assumed at a titre of 1:4. The conversion rates obtained from this group, known to be "triple negative' before vaccination, are shown in Table 33. One of the factors in the relatively low conversion rate for Type I antibodies may have been interference from other enteroviruses in March.
TABLE 33
POLIOMYELITIS CONVERSION RATES
by Type III. There was also a general marked correlation between the type of vaccine virus isolated from the faeces and the subsequent antibody response. Overall excretion rates of the vaccine types after feeding were 34% for Poliovirus Type I. 93% for Poliovirus Type II and 87% for Poliovirus Type III.
244.
From the 53 cases reported in 1963 none of the isolates were Type I, which in the previous year had caused 90% of the cases. The results of routine diagnostic examinations carried out by the Virus Laboratory on specimens received for virus isolations and serological studies are summarized in Table 34.
TABLE 34
Antibody Type
Type I
Type II
Type III
Kid
Total
r
+4
ISOLATION OF POLIOVIKUS
No, showing presence
of antibodies
Serological conversion rate
Fueces
89
Number Positive poliovirus examined
Type 1 Type JF Ope IF
30 12
Negative
46
3333
42
66%
Clinical caseS
Throat swabs
100
63 61
98.5% 95%
C.S.F.
17
27
Contact cases Convalescent cases
Facces
345
Faeces
34
29 3
311
79
241. Sera was also received from 50 unvaccinated children aged three months to five years who had been in reasonably close contact with vaccinated children. In the age-group 7-12 months ie. that most at risk, comparison of antibody levels found in April, 1963, with those found in unvaccinated children of the same age in December, 1962. showed a general increase of polio-antibody levels. This can be attributed to the spread of the vaccine virus in the community.
242. In December, sera were received from unvaccinated children aged three to twelve months to detect "triple-negative" children for further follow-up. Of these. 37 were from the age-group 7-12 months, and a comparison with the April survey showed a general percentage increase of 'triple negative' children-65% in December and 25% in April. Most noteworthy was the complete absence of antibody to Type I poliovirus in all 37 children tested; it can be presumed that these children had not been exposed to either the 'wild' or the 'vaccine' virus.
243. During the mass campaign in the first quarter of 1963, a control group of 79 'Triple-negative' children was surveyed by weekly rectal swabs for twelve weeks, poliovirus isolation and marker tests being carried out in cach case. After feeding of the virus, the results showed that the average duration of excretion was approximately five weeks and that Type fl was the dominant type after the first feeding followed
56
245. Commencing in December, samples of nightsoil from Kowloon and of Moore's swabs in sewage from Hong Kong were taken to obtain data on the prevalence of 'wild' and 'vaccine' strains of poliovirus. Two out of eight samples of nightsoil from Kowloon showed the presence of 'vaccine' poliovirus.
Respiratory Virus Identification
246. In March, 1963, the Virus Laboratory was designated a National Influenza Centre by the World Health Organization who supplied reagents for influenza virus studies.
247. Throat swabs were received from cases of respiratory infection in children and babies from the Paediatric Unit, Queen Mary Hospital. together with paired sera. Respiratory syncytial virus (R.S. virus) was isolated from four of these cases who were all under one year of age. All sera were tested for antibodies by complement-fixation technique and a more than four-fold antibody rise to the R.S. virus isolated was obtained in some of the cases. It is therefore evident that the virus does occur in Hong Kong and is likely to be an important cause of respiratory infection in children under the age of twelve months.
248. All sera received were also tested for complement-fixation antibodies to Influenza A, Influenza B. Adenovirus, Q-fever, and psit- tacosis. Results are shown in Table 35.
57