Flu Scan for May 01, 2018

Influenza attack rates
Flu spray vaccine and asthma

New review finds flu infects 1 in 5 unvaccinated kids, 1 in 10 adults

An updated analysis of the seasonal flu attack rate in unvaccinated people found that the virus infects 1 in 5 children each year and 1 in 10 adults, with symptomatic illness seen in about half of the infections. A team from Australia and New Zealand reported its findings yesterday in Vaccine.

The investigators noted that there's a lot of uncertainly and lack of data to guide estimates on the annual flu attack rate, which makes it difficult to plan vaccination programs and gauge the impact of future interventions. For their new analysis, they looked at 32 randomized, controlled vaccine trials containing 13,329 participants that reported on lab-confirmed flu in the placebo groups. Six were conducted before 2000, 3 covered the 2009 H1N1 pandemic period but only reported on rates for seasonal flu, and 8 reported on multiple flu seasons.

Overall, rates of symptomatic infection were highest in children (12.7%), followed by the elderly (7.2%) and all adults (4.4%). For both symptomatic and asymptomatic flu combined, the attack rates were 22.5% for children and 10.7% for adults. Older people had similar rates of symptomatic and asymptomatic infection.

The team found large variability among the studies, such as symptomatic attack rates in kids that varied from 5.3% to 29.8%. They also found differences in studies conducted before and after 2000, with attack rates for symptomatic flu lower in the more recent studies, which they said might reflect a real decline in attack rates, perhaps to changes in population immunity, improved prevention, or changes in testing.

The authors concluded that the estimates will allow more accurate modeling of flu prevention tactics, and they added that future studies might someday include high-quality observational studies that allow researchers to assess attack rates for different vaccination levels.
Apr 30 Vaccine abstract


Study finds no evidence of asthma long-term after nasal spray flu vaccine

Kaiser Permanente researchers found no evidence of increased risk of subsequent asthma diagnosis years later among children younger than 3 years of age who received live attenuated influenza vaccines, according to a study today in the Pediatric Infectious Disease Journal.

The researchers write, "Live-attenuated influenza vaccines (LAIVs) are not licensed in children younger than 2 years of age because of a wheezing safety signal that has not been fully elucidated." LAIV is administered as a nasal spray.

In 2000, Kaiser Permanente scientists conducted a placebo-controlled randomized clinical trial of LAIV in children. Because many of these children were still enrolled in Kaiser Permanente in 2014, the researchers involved in today's study could assess the long-term association between LAIV and asthma.

The team identified 1,151 children who were 12 to 35 months old at the time of the first study and had received two LAIV doses or a placebo. Of these, 767 were still Kaiser Permanents patients and were enrolled in the new study, and the investigators found no evidence of an increase in asthma diagnosis among those who had received LAIV at an early age.
May Pediatr Infect Dis J study

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