Biological properties of the Hong Kong influenza variants are described in relation to the isolation and identification of strains, sensitivity to nonspecific inhibitors, and serological diagnosis. Hong Kong virus strains were readily isolated in both eggs and monkey-kidney tissue cultures and were identified by haemagglutination-inhibition (HI) with chicken erythrocytes. The morphology, soluble antigen, and neuraminidase of Hong Kong isolates were similar to those of earlier A2 Asian influenza strains. Hong Kong haemagglutinins were related in varying degrees to previous human A2 and animal influenza viruses.The sensitivity of Hong Kong isolates to nonspecific haemagglutination inhibitors in serum varied widely. From least to most inhibitory, the ranking of sera of 8 animal species tested was: monkey, goat, chicken, human, rabbit, ferret, guinea-pig and horse. The same sera were treated with heat, trypsin, periodate, receptor-destroying enzyme and kaolin to determine the most effective way of removing nonspecific inhibitors. The results varied with the animal species involved.The A2 Asian antigen was nearly as effective as Hong Kong antigen in detecting antibody rises by HI tests. HI tests with either antigen were more efficient than complement-fixation tests for serodiagnosis of Hong Kong influenza, but for maximum efficiency both tests were required.

Animals↗

PubMed1969

Properties of the Hong Kong influenza virus. Antigenic relationship of the Hong Kong virus haemagglutinin to that of other human influenza A viruses.

The magnitude of antigenic change of the Hong Kong strains from the earlier influenza A2 strains was compared with previous antigenic changes among the type A viruses. Representative type A strains recovered from man during the years 1933 through 1969 were examined by reciprocal haemagglutination-inhibition, neutralization and neuraminidase-inhibition tests, using antisera produced in chickens. Phenograms or "family trees" were constructed, using numerical taxonomic methods based on cluster analysis of similarity coefficients. By the use of numerical taxonomic methods the inequality of the antigenic relationships among presently recognized classes becomes evident. Antigenic dissimilarities between A0 and A1 strains seen in phenograms constructed from reciprocal haemagglutination-inhibition and neutralization tests were of lower magnitude than dissimilarities between A1 and A2 strains and should not be given equal emphasis. The degree of antigenic dissimilarity between the Hong Kong-like strains and the early A2 strains was even less than that between A0 and A1.The authors stress the need for a new system for identifying and classifying human influenza A strains.

Animals↗

PubMed1969

Studies with inactivated influenza vaccines purified by zonal centrifugation. 1. Adverse reactions and serological responses.

High (3000 CCA units) and standard low (300 CCA units) doses of formalin-inactivated influenza vaccines purified by zonal ultracentrifugation were evaluated in a double-blind manner for adverse reactions and antibody responses in a high school population and in 2 adult populations.The fewest local and systemic reactions were produced by subcutaneous administration of the low doses of purified monovalent A2/Aichi/2/68, A2/Japan/170/62, and B/Massachusetts/3/66 vaccines. The high doses of A2/Japan and A2/Aichi vaccines produced 2-3-fold greater incidence of adverse reactions but did not exceed that observed with the commercial vaccines. The 3000 CCA units of B/Mass. vaccine produced more frequent and more severe systemic reactions than the polyvalent vaccine.Neither the A2/Japan vaccine nor the commercial vaccines stimulated a significant serum antibody response to A2/Aichi.The homologous serum antibody response to an Aichi vaccine was excellent in all 3 populations. A2/Aichi vaccines produced higher heterologous A2/Japan titres than did the A2/Japan vaccines. It was demonstrated that high doses of purified influenza vaccine can be given safely, and that 10-fold increases in vaccine concentration produce 2-3-fold increases in antibody titre.

Adolescent↗

PubMed1969

Studies with inactivated influenza vaccines purified by zonal centrifugation. 2. Efficacy.

High (3000 CCA units) and standard low (300 CCA units) doses of the monovalent purified vaccines described in an earlier paper were evaluated in a double-blind manner in 2 adult populations for protective effectiveness against illness caused by the Hong Kong influenza virus. Epidemics in both populations occurred 4-6 weeks after single injections of vaccine were given.The attack rates among recipients of low or high doses of A2/Japan vaccines in a prison were virtually identical to those among the control groups receiving B/Massachusetts vaccines. The attack rate among those receiving 3000 CCA units of Aichi vaccine was nearly 70% less than the rate among recipients of A2/Japan or B/Mass. vaccines. Similarly, in a retirement community the attack rate among the recipients of 3000 CCA units of Aichi vaccine was 50%-70% lower than the attack rate among the recipients of the A2/Japan vaccine. In both populations, recipients of high doses of Aichi vaccine who later became ill tended to have less morbidity, fewer and lower fevers, and shorter stays in bed. Attack rates among the groups receiving low doses of Aichi vaccine were somewhat lower than rates among those receiving A2/Japan or B/Mass. vaccines, but the effect was not statistically significant. Divalent and polyvalent commercial vaccines were also without protective effect.The results indicate that optimally constituted influenza vaccines at standard dosage levels have little, if any, effectiveness and that even very large doses of vaccine do not approach the high degrees of effectiveness that have been achieved with other virus vaccines.

Adult↗

PubMed1968