COVID-19 vaccination plans in Latin America and the Caribbean: a multi-country comparative analysis of prioritization strategies.

OBJECTIVES: This study aimed to synthesize and compare the prioritization strategies outlined in the national vaccination plans (NVPs) against Coronavirus Disease 2019 (COVID-19) developed by countries in the Latin America and Caribbean (LAC) region. STUDY DESIGN: We conducted a comparative policy analysis based on COVID-19 NVPs. METHODS: We conducted a search strategy in three stages to identify NVPs for COVID-19 across 41 countries/territories in the LAC region. Sources included official governmental repositories, complementary Google searches, and less formal documentation. We extracted key variables and conducted a comparative policy analysis based on the prioritization criteria and specific prioritization groups. RESULTS: The study identified 52 NVPs for COVID-19, corresponding to 27 (65.8 %) out of 41 countries/territories in the LAC region. Official national websites yielded documents for 12 countries. All NVPs included frontline healthcare personnel in the first prioritization phase/stage, whilst some included residents of long-term healthcare facilities, adults aged 60 years or more, and people with disabilities. The decision criteria for prioritization were declared in 14 countries/territories. Ethical considerations declared in five NVPs included human welfare, equality, solidarity, equity, and social justice as values. CONCLUSION: The early stages of vaccination rollout in LAC countries prioritized protection of the healthcare system and epidemiological risk for severe disease. Few countries included ethical considerations in their NVPs, and global inequities in vaccine access and distribution led to varied protections for vulnerable populations across LAC. This analysis highlights the need for improved emergency-response capacity, planning, and enhanced multilateral cooperation in the LAC region for future public health emergencies.

Intra-cellular and extra-cellular growth of L. monocytogenes in chick embryo fibroblast cell culture.

The growth of L. monocytogenes in isolated chick embryo fibroblast cell culture was studied. Hanks balanced salt solution and Eagles minimal essential medium were shown to support a limited growth of L. monocytogenes. Extra-cellular growth on the maintenance medium occurs for 48 h prior to the establishment of intra-cellular organisms. As the uptake of the parasite by the cell culture takes place, intra-cellular replication begins with subsequent release of the organisms into the surrounding medium. The organism continues to replicate intra-cellularly until all the cell culture is destroyed.

The effect of progesterone on the growth and virulence of Listeria monocytogenes.

Progesterone was examined for action on the virulence of Listeria monocytogenes and the toxicity of its haemolysin. Progesterone at concentrations between 5 and 20 micrograms/ml reduced the numbers of L. monocytogenes over the first two hours of growth. Virulence and haemolysin toxicity were assessed using the allantoic sac route of inoculation into embryonated hens eggs. Increasing the concentrations of progesterone in the culture medium resulted in a decrease in the mortality of chick embryos inoculated with either organisms, or cell-free extracts or purified haemolysin. Progesterone had no effect on the lethality of pre-formed haemolysin.

Role of haemolysin and temperature in the pathogenesis of Listeria monocytogenes in fertile hens' eggs.

The haemolysin produced by Listeria monocytogenes at 37 degrees C and 4 degrees C was examined in fertile hens' eggs. Organisms, cell free extracts and purified haemolysin derived from broth cultures grown at the lower temperature were more pathogenic for chick embryos, induced higher mortality with toxic changes in the embryos. These effects were most pronounced with the purified haemolysin as shown by LD50 determinations and following inoculation of constant haemolytic doses. Pathological changes induced by the haemolysin included sub-cutaneous haemorrhage due to endothelial damage, hepatosplenomegaly with macroscopic and histological lesions in heart, spleen and liver in the absence of an inflammatory response. At the cellular level, the myocardial tissue, and hepatocyte structure were destroyed with intravascular haemolysis, fatty degeneration of mitochondria, dilation of endoplasmic reticulum and distortion of liver cell nuclear membranes evident. The mortality and morphological data showed an increase in virulence for Listeria after culture at 4 degrees C compared with 37 degrees C and suggested a more cytotoxic component of the haemolysin which was activated at lower temperatures.

Role of lipid in butylatedhydroxyanisole (BHA) resistance of Listeria monocytogenes.

The lipid content of Listeria monocytogenes 5214m was increased by successive subculturing in a glycerol medium. Fattened cells showed considerably greater resistance to Butylatedhydroxyanisole (BHA). Polar lipids and fatty acid composition of four cultures with different BHA sensitivity were analysed. They are basically similar but the resistant cultures had a lower percentage of unsaturated and anteiso to saturated and iso fatty acids.

Pathogenesis and growth of Listeria monocytogenes in fertile hens' eggs.

The LD50 for 15-day old chicken embryos inoculated with Listeria monocytogenes into the allantoic sac was determined. The growth cycle of the organism was investigated in different tissues and fluids derived from embryonated eggs following inoculation with a suspension of L. monocytogenes equivalent to the LD50. Eggs receiving doses of 100 and 1000 times the LD50 were used to examine the effect of high doses on the pathogenesis and growth of Listeria in ovo. The pattern of growth of the organism in embryonic blood showed two distinct peaks and correlated with these was the development of large and small pock lesions on the chorioallantoic membrane. Bacterial growth in the internal organs exhibited a single peak. Histological and electron microscopic evidence indicated that the primary cellular damage was due to a soluble haemolysin present prior to the establishment of the organism within the tissues.

Pathogenicity of natural and experimental listeriosis in newly hatched chicks.

The pathogenicity of Listeria monocytogenes for newly hatched chickens exposed to natural infection was examined. Organisms entered through the alimentary tract and dissemination followed bacteraemia. Among a number of symptoms recorded were unilateral and bilateral toe paralysis. In addition to gross abnormalities in the following tissues, histological lesions were seen in the liver, spleen, heart and kidneys of all infected chicks but brain lesions were observed only in birds with central nervous system involvement. The organism was recovered from some tissues derived from apparently healthy chicks as well as those with listeriosis. The use of trypsin in the isolation process increased the probability of a positive result from tissues, reduced the storage time needed and had no adverse effect on the rate of organism growth.

Infection, haemorrhagia and death of chick embryos experimentally inoculated with Listeria monocytogenes by the intra-allantoic route.

When allantoic sacs of embryonated (SPF) chicken eggs were inoculated with different doses to investigate the pathogenicity of two strains of Listeria monocytogens (4379 and NCTC 5214), infection resulted which spread rapidly throughout the embryonated eggs. When low doses were used small pock lesions on the chorio-allantoic membrane (CAM), generalized haemorrhage (especially on the head region) and deaths of the embryos with necrotic foci on the liver and heart were observed. Neither the pock lesions nor the haemorrhage were detected in embryos dying from high doses of the bacterium. Bacteria were recovered from the CAM's, allantoic fluids, amniotic fluids and selected organs of the dead embryos. The pathogenicity was shown to be strain dependent, strain 4379 being more pathogenic than strain NCTC 5214. In vitro studies indicated that brain homogenates of uninoculated chicken embryos are not inhibitory to Listeria monocytogenes at 37 degrees C and will increase the viable count.

Survival of Listeria monocytogenes in high salt concentrations.

The bactericidal effects of high concentrations of common salt has been determined in a laboratory medium for Listeria monocytogenes strain (1, 2a, No. 18). The survival time for the organism was followed at three different incubation temperatures (4, 22, 37 degrees C). The influence of temperature on the action of salt is discussed.

Low temperature virulence of Listeria monocytogenes in the avian embryo.

The chick embryo was used to investigate the pathogenicity of Listeria monocytogenes when inoculated into the air sac. One strain (NCTC 5214) of L. monocytogenes was found to be more virulent for chick embryos when grown at low temperatures, while another strain (NCTC 5105) did not produce this effect. This method was found to be reliable and reproducible and the chick embryo was found to be a more sensitive in vivo assay for virulence than the mouse.

Immunofluorescent identification of Listeria monocytogenes.

A fluorescent antibody technique for the rapid diagnosis and identification of L. monocytogenes in smears, impression smears from tissues of animals dead from listeriosis, and in meat and milk is described. The technique could well be exploited for detecting L. monocytogenes in meat and meat products, animal tissues, and in milk provided that it is supplemented with adequate controls. The technique has been compared with conventional cultural technique and found to be superior as far as the time factor is concerned. The use of the technique also demonstrates the possibility of actually determining the serological type concurrently.

Further data on the characters of Listeria strains.

The composition of a minimal medium suitable for the demands of modern genetical work is described. The nutritional requirements of some 15 strains of L. monocytogenes were studied on this medium. DL-6,8-thioctic acid was not essential. The organisms also grew without thiamine but for a convenient colony size this vitamin had to be used. The presence of Fe++, Mg++, and Ca++ ions as well as a low redox potential supplied by thioglycollate was necessary. There was some difference in the amino acid requirements of the strains. The most common demand was for leucine, iso-leucine, valine, and cysteine. The serotype, agglutinability, hemolytic effect, virulence, and nutritional requirements of the Listeria were compared. It seems that these properties are not consistently linked. Two 'EMS' mutants were also studied. The arginine, glutamine, and methionine metabolism of the auxotrophic mutant 025/4/4 was damaged and its virulence was lost. Data connected with the virulence markers of Listeria are discussed.