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The 17D-derived yellow fever (YF) vaccines have had an excellent record of their safety among millions of recipients. Recently, extensive viral dissemination in seven vaccinees, aged 5-79 years, with just one survivor posed a serious challenge for vaccine manufacturers. Prospective evaluations of yellow fever vaccine bulk suspensions for their viscerotropism and neurovirulence in primates or an alternate animal should minimize identical viral dissemination among prospective recipients of YF vaccines.

While measles, pertussis and tetanus were responsible during the early 1990s for nearly two million deaths in developing countries, no deaths were attributable to them in industrialized countries. More than 96% of global deaths by communicable diseases were also from developing countries. Respiratory infections ranked first in communicable morbidity at all ages. Even though vaccines of bacterial or viral origin or a prophylactic for passive immunization are produced in 24, 16 and 15 developing countries, respectively, none of the developing countries manufactures a plasma-derived prophylactic or biological response modifier. Nearly every country relies on import of one or more vaccines. The suboptimal performance of otherwise meritorious products has been due to faulty vaccine administration practices. Expanding populations, poverty and lack of education, cold-chain defects, and inadequate facilities for transport of vaccines to target populations in remote areas have been responsible for the poor performance of vaccines in the community. Mounting foreign debts and budgetary strains resulting from the care and prevention of AIDS/HIV have considerably strained national and international efforts to offer routine vaccinations in childhood and pregnancy. This dismal situation could be tackled through research to obtain environmentally stable products for prophylactic use and monoclonal antibody formulations for passive immunization, and through international financial and technical support. All countries should exercise some technical control of the quality of imported and indigenous vaccines during their use for curative or prophylactic purposes. The involvement of private clinicians in immunizations would strengthen national efforts for control of communicable diseases including AIDS, but this is not enough if the local factors cited above are not improved.

Failures of oral poliovirus vaccine lots in developing countries are explained by interference during their 'take' by other enteroviruses colonizing the host intestinal system. Oral poliovirus vaccines, on their part, have also exerted an interfering effect on multiplication of other enteroviruses. Apart from the intrafamilial enterovirus interference, oral poliovirus vaccine has not spared rotaviruses.

A substantial rise in the number of AIDS cases has been observed during the past year in many African countries, and HIV-2 indigenous transmission and increased disease have since gained importance in Senegal. Both for HIV-1 and HIV-2 diagnosis, ELISA positivity is followed by a Western blot test for specific antibodies. The serum samples are stored at sub-zero temperatures both during shipment and storage while awaiting serological testing. Attempts have been made to use dried blood on filter papers for AIDS diagnosis, in 35 samples from Africa and 10 from USA, along with corresponding serum samples. The concordance has been good with an almost invariable ELISA confirmation on Western blot, no selective loss in any of the bands in Western blot and the Pearson coefficient value for ELISA testing on serum and dried blood lots of 0.85. Based on the data obtained during the intentional exposure of blood-impregnated filter papers, from nine HIV-positive and one HIV-negative patient from the USA, to varying temperatures and humidity for different intervals, blood collection on filter paper would appear to have emerged as a satisfactory procedure for HIV seroepidemiological studies.

The scepticism about the future utility of newer biologicals towards reducing disease morbidity or mortality at the public health or application level can be regarded as appropriate. The financial or research inputs into producing anti-idiotypic, subunit, cloned or genetically engineered products may not be transcribed to the field level due to political or economic impediments and the putative breakdown of any specific activity at the application level, as with the conventional immunobiologicals, may also negate the utility of the newer products. Such an eventuality should be overcome by planning, during the pre-licensure phase, appropriate accelerated degradation tests on newer biologicals.