But most (77%) of these infections showed no symptoms, and only around 17% of people with PCR-confirmed influenza visited their doctor. Compared with some seasonal flu strains, the 2009 pandemic strain caused substantially milder symptoms. The study indicates that primary-care surveillance greatly underestimates the extent of infection and illness in the community. The rate of influenza across all winter seasons was on average 22 times higher than rates of disease recorded by the Royal College of General Practitioners Sentinel Influenza-Like Illness Surveillance Scheme. According to Dr Hayward, “Despite its mild nature, the 2009 pandemic caused enormous international concern, expense, and disruption. We need to prepare for how to respond to both mild and severe pandemics. To do this we need more refined assessments of severity, including community studies to guide control measures early in the course of a pandemic and inform a proportionate response.” In a linked comment, Dr Peter William Horby from the Oxford University Clinical Research Unit in Vietnam says, “Surveillance of medically attended illnesses provides a partial and biased picture, and is vulnerable to changes in consulting, testing, or reporting practices. As such, it is clear that reliable estimates of the infection and clinical attack rates during the early stages of an influenza epidemic requires the collection of standardised data across the whole range of disease severity, from the community, primary care, and secondary care.”
Low 2012–13 Influenza Vaccine Effectiveness Associated with Mutation in the Egg-Adapted H3N2 Vaccine Strain Not Antigenic Drift in Circulating Viruses In summary, our findings underscore the need to monitor vaccine viruses as well as circulating strains to explain vaccine performance….a better understanding of specific mutations related to egg-adaptation and most influential upon vaccine protection is needed. We highlight the immuno-epidemiologic complexity that may further influence VE [vaccine effectiveness], including agent-host interactions and prior antigenic exposures. This complexity is daunting to consider but critical to confront in improving influenza prevention and control. Also see the news article, Flu study solves puzzle of vaccine’s ineffectiveness against H3N2 Most of the world’s flu vaccine supply is produced using a system where influenza viruses are grown in hen’s eggs. In the process, the viruses have to adapt — acquire some mutational changes — to grow in eggs. The process has the potential to introduce mutations that weaken the protection that vaccine virus can offer. Skowronski said many of the scientists and public health officials she has presented her data to have been shocked to realize mutations could be introduced in the production process.
A vaccine against serogroup B Neisseria meningitidis: dealing with uncertainty uncertainty remains about the breadth of protection the vaccine might induce against the diverse serogroup B meningococci strains that cause disease. We discuss drawbacks in the techniques used to estimate coverage and potential efficacy of the vaccine, and their effects on estimates of cost-effectiveness, both with and without herd immunity….future use of the vaccine must be followed by rigorous post-implementation surveillance to reassess its value to health systems with directly recorded epidemiological data.
those infected there were 69 respiratory illnesses per 100 person-influenza-seasons compared with 44 per 100 in those not infected with influenza. The age-adjusted attributable rate of illness if infected was 23 illnesses per 100 person-seasons (13—34), suggesting most influenza infections are asymptomatic. 25% (18—35) of all people with serologically confirmed infections had PCR-confirmed disease. 17% (10—26) of people with PCR-confirmed influenza had medically attended illness. These figures did not differ significantly when comparing pandemic with seasonal influenza. Of PCR-confirmed cases, people infected with the 2009 pandemic strain had markedly less severe symptoms than those infected with seasonal H3N2. Also see interpretation, Three-quarters of people with seasonal and pandemic flu have no symptoms. The results show that on average 18% of the unvaccinated community were infected with influenza each winter season—19% during prepandemic seasons and 18% during the 2009 pandemic.
