CDC: Too early to predict future of H7N9 outbreak

It is still too early to make any predictions about what will happen with the novel influenza A(H7N9) virus this fall, according to Michael Shaw, PhD, associate director of Laboratory Science for the CDC’s Influenza Division.

“The big question right now is what will happen in the Southern Hemisphere because they are just heading into their flu season now,” Shaw told Infectious Diseases in Children. “Although we haven’t seen human-to-human transmission yet, we are not expecting any immunity to H7N9 if it does happen, which is why we are concerned. We are not hitting the panic button yet, but we are watching very closely.”

Michael Shaw

As of April 9, the virus has infected 28 people and killed eight in China, Shaw said. There has been no human-to-human transmission documented thus far, but the virus has been found is pigeons, chickens and quail, all farm-raised animals grown for commercial purposes.

Compared with the 1997 avian influenza outbreak of H5N1 — the first time an avian virus was seen in humans — the H7N9 outbreak is different because the virus does not seem to be noticeably pathogenic among birds, Shaw said. The virus that appeared in 1997 and reappeared in 2003 was causing birds to die, which made it obvious that there was a problem.

Vaccine development

CDC is working on a vaccine for H7N9, Shaw said. The plan is to follow every possible avenue to develop a vaccine. In addition to egg-based vaccine manufacturers, Novartis is currently working on a cell-based vaccine.

“We’re not going to leave anything to chance,” Shaw said. “We are going to try everything we can think of.”

A definite alarm to begin manufacturing the vaccine will be when there is evidence of human-to-human transmission, Shaw said. However, the process toward manufacturing a vaccine happens in stages. Currently, there are isolated cases of H7N9, and most of them probably had some bird exposure at some point. There has not yet been any evidence of human-to-human transmission, even among close contacts. Chinese health authorities have increased surveillance among health care workers.

“We saw limited human-to-human transmission with H5N1,” Shaw said. “Parents taking care of a sick child will get sick, but they had very intimate contact for long periods of time. What we worry about is when the virus doesn’t follow that chain of transmission. When we can’t find an epidemiologic link, and cases are popping up all over, that indicates that transmission is going a lot more easily.”

Advising physicians

The virus has been sensitive to the neuraminidase inhibitors zanamivir (Relenza, GlaxoSmithKline) and oseltamivir (Tamiflu, Genentech). There has been resistance to adamantines, so they should not be considered, Shaw said.

In the past, human cases of H7 strains have presented with conjunctivitis as the primary symptom, but this strain appears to be different. Special attention should be paid to patients with elevated temperature. Shaw advises that avian influenza infections in humans, especially in children, often do not manifest as classical influenza-like illness. In addition, sometimes there are neurological symptoms associated with avian influenza.

Most of the cases have been in adults, primarily the elderly. There has been just one pediatric case in a 4-year-old.

“We have no idea why there has been [only one] pediatric case to date, but it’s possible that the infection is mild in children, and therefore they are not seeking medical attention,” Shaw said. “The Chinese health authorities have tested more than 500 contacts and all have come out negative. It’s hard to say what’s going on. It may be that we are only seeing the serious cases because they are hospitalized.”

So far, there are no travel restrictions to China, but the CDC has issued a health advisory asking physicians to be alert for influenza-like illness among those who recently traveled to China.

Officials in Taiwan and Hong Kong have ramped up their screening efforts and screened recent travelers, but have not had any positive cases, Shaw said. Any influenza type A isolates that do not react to H1N1 or H3N2 are forwarded to the CDC for investigation. None of the isolates received so far have been positive, he added.

Physicians can obtain more information about interim recommendations for case investigation and testing, infection control measures and treatment by visiting http://emergency.cdc.gov/HAN/han00344.asp.

Disclosure: Shaw reports no relevant financial disclosures.