Herd immunity from immunising children against influenza
There is circumstantial but insufficient high-level evidence that immunising schoolchildren against influenza protects their contacts, that is confers herd immunity. A Canadian study tested this hypothesis using a cluster randomised study design. Schoolchildren aged 3–15 years in Hutterite colonies (Anabaptist rural communities) were randomised to receive the standard inactivated trivalent influenza vaccine (intervention) or hepatitis A vaccine (control). Each colony consists of 60–120 people in a tight-knit community with its own school.
Overall, inactivated influenza vaccine was 59% effective in protecting all study participants, both those immunised and those not, against laboratory-confirmed influenza (PCR positive). It also reduced the incidence of proven influenza in non-recipients of influenza vaccine from 7.6% in control colonies to 3.1% in intervention colonies, giving a protective efficacy of 61% (95% confidence interval (CI) 8–83%) for contacts.
This important study provides the best proof to date that immunising schoolchildren against influenza confers significant herd immunity which protects their community contacts.
Reviewer: David Isaacs, firstname.lastname@example.org
Mixed handedness and mental health
There is some evidence that alterations in the right hemisphere of the brain are associated with both attention-deficit/hyperactivity disorder (ADHD) and dyslexia. The authors believe that non-right-handedness may be a risk factor for neurobehavioural difficulties and mixed-handedness may be more important than left-handedness. A Northern Finland birth cohort study collected questionnaire data on handedness of over 8000 children at 8 years of age. Parents were asked if their child was right-handed, left-handed or mixed-handed. The proportions were 90.9%, 8% and 1.1%, respectively. A follow-up questionnaire at age 15–16 years enquired about ADHD symptoms using the Strengths and Weakness of ADHD symptoms and Normal behaviour scale and was completed by almost 80% of adolescents.
At 8 years old, 16.6% of children had problems with speech and language, and mixed-handedness but not left-handedness was associated with about twice the risk of language problems and a trend towards more behaviour problems. At 16 years of age, 4.4% of right-handed children had inattention and/or hyperactivity–impulsivity, while in comparison 14% of mixed-handed children had inattention (odds ratio 2.96, 95% CI 1.38, 6.35), although they were not more hyperactive. This study suggests that it might be possible to target the 1% of children with mixed-handedness for early intervention.
Probiotics, necrotising enterocolitis and mortality
A meta-analysis of 11 randomised controlled trials of probiotics in over 2000 preterm (<34 weeks), very low birthweight (<1500g) neonates showed a 65% reduction in necrotising enterocolitis (NEC) (relative risk (RR) 0.35, 95% CI 0.23, 0.55) and a 58% reduction in all-cause mortality (RR 0.42, 95% CI 0.29, 0.62). Thus, only 20 babies need to be treated with probiotics to prevent one death.
This effect was not merely reducing deaths from NEC, and since probiotics had no effect on blood-culture positive sepsis, the mechanism for the reduction in mortality remains speculative.
The meta-analysis stimulated conflicting editorial comments. One by Soll argued caution, pointing out that the trials studied many different probiotic preparations and feeding regimes in relatively mature babies. The other by Tarnow-Mordi et al. argued that it was reasonable to combine studies if you were looking for a class effect of probiotics and urged a change in practice to routine use of probiotics, although access to quality-controlled, licensed products is problematic. Tarnow-Mordi et al. also discussed the ethics of continuing enrolment of babies in trials and the need for fully informed consent. A flurry of letters followed, mostly cautious about overinterpreting the meta-analysis and urging further studies.
No such thing as a free lunch: undeclared conflicts of interest
In 1998, a New England Journal of Medicine paper reported that authors with financial ties to drug manufacturers were more likely than those without ties to publish recommending use of calcium channel antagonists. Worryingly, only 2 of the 70 authors with financial ties declared them.
There is current controversy over whether or not the diabetes drug rosiglitazone increases the risk of myocardial infarction. Researchers from the Mayo Clinic performed a systematic review of authors' affiliations with industry (declared in the published papers and found elsewhere, e.g. online) and their written position on the controversy. Only 53% of published papers included a conflict of interest statement. Unsurprisingly, the 90 authors with financial conflicts of interest were three to seven times more likely to recommend use of rosiglitazone. Disclosure had improved since 1998, but still 21 (23%) of the 90 articles did not disclose financial links and 3 of the 21 articles published statements that there was no conflict of interest.