Against the backdrop of four new H7N9 influenza illnesses reported from China today, a detailed look at the second wave of the outbreak reveals that cases are trending slightly younger, with a lower case fatality rate (CFR), though severe pneumonia is still one of the disease's hallmarks.
So far more than 80 new cases—the large majority from the first of the year—have been reported in the outbreak's second spike that began in October. Over the past few weeks China has often reported five to seven new cases each day, equaling the pace seen during last spring's first-wave peak.
Cases trending younger, less deadly?
World Health Organization (WHO) experts said today in their latest risk assessment that most cases in the first wave involved middle-aged or older men, but the age distribution in the new wave isn't as skewed toward older age-groups. The mean age in the new surge of cases is slightly lower than the first wave: 52 years compared with 58 years.
H7N9 is still striking males more frequently than females, and the CFR is not as high as the outbreak's first wave, the WHO said. It cautioned, however, that CFR patterns need to be monitored closely, because many of the recently infected patients are still hospitalized. Some milder cases have been reported, but it's clear that H7N9 infections are marked by rapidly progressing severe pneumonia, according to the risk assessment.
Lab analysis of H7N9 samples from patients, animals, and the environment collected during the second wave shows that the hemagglutinin (HA) and neuraminidase (NA) genes are similar to viruses from the first wave, the report said. It added that they are also similar to the influenza A/Anhui/1/2013 strain recommended for H7N9 vaccine development.
Tests on a subset of recent viruses to monitor for antiviral resistance have identified no markers linked to resistance to neuraminidase inhibitors, including oseltamivir (Tamiflu) and zanamivir (Relenza).
Resistance to frontline treatments such as oseltamivir and zanamivir has been a worry since the outbreak's early days, when an NA resistance marker was found in one of the first three lab-confirmed H7N9 cases. The resistant viruses have also been linked to treatment failures in some severely ill patients.