A/PR/8/34-England/939/69 (H3N2), clone 64d (2, 10), another attenuated recombinant, was selected and cloned in eggs and in chorioallantoic membrane bits.A/PR/8/34-England/42/72 (H3N2), clones MRC 2 MRC 5, and MRC 7, A/PR/8/34 (HO-England/42/72 (N2), clone MRC 3, and A/England/42/72 (H3)-PR/8/34 (NI), clone MRC 8, were recombinants used for experimental studies of live vaccines (4). A/England/72/72 (H3N2) was antigenically equivalent to A/Hong Kong/68 and was used for recombination and for volunteer experiments (unpublished data). A/Port Chalmers/1/73 (H3N2), a wild virus, was recombined with A/PR/8/34 to give an H3N2 clone, MRC 9. This was recombined with A/PR/8/34 to give another H3N2 clone, MRC 11 (4). Four H3N2 recombinants produced from A/Okuda/57 (H2N2) and A/Finland/4/74 (H3N2), clones WRL 94, WRL 95, WRL 100, and WRL 105 322 on August 3, 2020 by guest http://iai.asm.org/ Downloaded from

Epidemiological studies in naturally infected persons have shown that there is a significant relation between antibody levels to the current circulating virus and morbidity. Serological findings and morbidity data suggest: (1) that the serological survey is a more sensitive indicator for influenza outbreaks than is the clinical diagnosis and (2) that the 5-14 age group is first affected when an epidemic of influenza starts off. Consequently, school children may be the major source of influenza into family units and, therefore, among older segments of the population. Exploring the relationships between influenza morbidity and natality, as well as influenza morbidity and mortality under 1 year of age, values of <0·001 (Student's t-test) were obtained. The linear regression analysis showed that both relationships were represented as straight lines. From the results it seems logical to utilize the available vaccine for the protection of infants, school children and pregnant women. The vaccine-induced protection can offer significant, although not total, protection of the whole population and prevent obstetrical accidents.