Evaluation of rotavirus vaccines in Asia—Are there lessons to be learnt?

Lymphoid tissue fibrosis is associated with impaired vaccine responses

Vaccine responses vary by geographic location. We have previously described how HIV-associated inflammation leads to fibrosis of secondary lymph nodes (LNs) and T cell depletion. We hypothesized that other infections may cause LN inflammation and fibrosis, in a process similar to that seen in HIV infection, which may lead to T cell depletion and affect vaccine responses. We studied LNs of individuals from Kampala, Uganda, before and after yellow fever vaccination (YFV) and found fibrosis in LNs that was similar to that seen in HIV infection. We found blunted antibody responses to YFV that correlated to the amount of LN fibrosis and loss of T cells, including T follicular helper cells. These data suggest that LN fibrosis is not limited to HIV infection and may be associated with impaired immunologic responses to vaccines. This may have an impact on vaccine development, especially for infectious diseases prevalent in the developing world.

Household catastrophic healthcare expenditure and impoverishment due to rotavirus gastroenteritis requiring hospitalization in Malaysia

BACKGROUND

While healthcare costs for rotavirus gastroenteritis requiring hospitalization may be burdensome on households in Malaysia, exploration on the distribution and catastrophic impact of these expenses on households are lacking.

OBJECTIVES

We assessed the economic burden, levels and distribution of catastrophic healthcare expenditure, the poverty impact on households and inequities related to healthcare payments for acute gastroenteritis requiring hospitalization in Malaysia.

METHODS

A two-year prospective, hospital-based study was conducted from 2008 to 2010 in an urban (Kuala Lumpur) and rural (Kuala Terengganu) setting in Malaysia. All children under the age of 5 years admitted for acute gastroenteritis were included. Patients were screened for rotavirus and information on healthcare expenditure was obtained.

RESULTS

Of the 658 stool samples collected at both centers, 248 (38%) were positive for rotavirus. Direct and indirect costs incurred were significantly higher in Kuala Lumpur compared with Kuala Terengganu (US$222 Vs. US$45; p<0.001). The mean direct and indirect costs for rotavirus gastroenteritis consisted 20% of monthly household income in Kuala Lumpur, as compared with only 5% in Kuala Terengganu. Direct medical costs paid out-of-pocket caused 141 (33%) households in Kuala Lumpur to experience catastrophic expenditure and 11 (3%) households to incur poverty. However in Kuala Terengganu, only one household (0.5%) experienced catastrophic healthcare expenditure and none were impoverished. The lowest income quintile in Kuala Lumpur was more likely to experience catastrophic payments compared to the highest quintile (87% vs 8%). The concentration index for out-of-pocket healthcare payments was closer to zero at Kuala Lumpur (0.03) than at Kuala Terengganu (0.24).

CONCLUSIONS

While urban households were wealthier, healthcare expenditure due to gastroenteritis had more catastrophic and poverty impact on the urban poor. Universal rotavirus vaccination would reduce both disease burden and health inequities in Malaysia.

Immunology of gut mucosal vaccines

Understanding the mechanisms underlying the induction of immunity in the gastrointestinal mucosa following oral immunization and the cross-talk between mucosal and systemic immunity should expedite the development of vaccines to diminish the global burden caused by enteric pathogens. Identifying an immunological correlate of protection in the course of field trials of efficacy, animal models (when available), or human challenge studies is also invaluable. In industrialized country populations, live attenuated vaccines (e.g. polio, typhoid, and rotavirus) mimic natural infection and generate robust protective immune responses. In contrast, a major challenge is to understand and overcome the barriers responsible for the diminished immunogenicity and efficacy of the same enteric vaccines in underprivileged populations in developing countries. Success in developing vaccines against some enteric pathogens has heretofore been elusive (e.g. Shigella). Different types of oral vaccines can selectively or inclusively elicit mucosal secretory immunoglobulin A and serum immunoglobulin G antibodies and a variety of cell-mediated immune responses. Areas of research that require acceleration include interaction between the gut innate immune system and the stimulation of adaptive immunity, development of safe yet effective mucosal adjuvants, better understanding of homing to the mucosa of immunologically relevant cells, and elicitation of mucosal immunologic memory. This review dissects the immune responses elicited in humans by enteric vaccines.

Co-dominance of G1 and emerging G3 rotaviruses in Hong Kong: a three-year surveillance in three major hospitals

BACKGROUND

The World Health Organization recommends rotavirus vaccines be included in all national immunization programs as part of a strategy to control diarrhoeal diseases. Sentinel surveillance is advised to monitor impact post-vaccine introduction and to document changes in genotype distribution.

OBJECTIVES

To determine the molecular epidemiology of circulating rotaviruses in Hong Kong prior to implementation of universal rotavirus vaccination.

STUDY DESIGN

From December 2004 through December 2007, 830 rotavirus-positive stool samples from subjects admitted for acute diarrhea to three major hospitals in Hong Kong were examined. The electropherotypes, and the G and P genotypes of these rotaviruses were determined. Phylogenetic analysis of the VP7 gene was performed.

RESULTS

G3P[8] was the dominant genotype (46.1%), followed by G1P[8] (36.5%) and G9P[8] (9.2%). A total of 35 electropherotypes were identified. The G3 and G1 strains had high sequence similarities among themselves and were clustered with strains from Asia particularly mainland China. The G9 strains were clustered with the globally spreading strains. G12 and G4 were not found. The prevalence of rotavirus infection peaked in winter season when temperature was low, atmospheric pressure was high, relative humidity was low and rainfall was negligible.

CONCLUSIONS

Genotype G3 and G1 were the dominant rotaviruses circulating in Hong Kong between 2004 and 2007. Strains were mainly related with those from mainland China. Ongoing surveillance of circulating genotypes should continue in anticipation of universal rotavirus vaccine introduction.

Immunogenicity and efficacy of oral vaccines in developing countries: lessons from a live cholera vaccine

Oral vaccines, whether living or non-living, viral or bacterial, elicit diminished immune responses or have lower efficacy in developing countries than in developed countries. Here I describe studies with a live oral cholera vaccine that include older children no longer deriving immune support from breast milk or maternal antibodies and that identify some of the factors accounting for the lower immunogenicity, as well as suggesting counter-measures that may enhance the effectiveness of oral immunization in developing countries. The fundamental breakthrough is likely to require reversing effects of the 'environmental enteropathy' that is often present in children living in fecally contaminated, impoverished environments.