H7N9 Case Numbers Stalled, But Pandemic Potential Remains

Stay Vigilant, Initiate Treatment Early, CDC Urges

May 16, 2013 05:05 pm Matt Brown

Despite the fact that since May 7, no new human cases of avian influenza A (H7N9)(www.cdc.gov) infection have been reported in China -- the only country affected by the deadly virus to date -- the CDC continues to encourage medical professionals in the United States to maintain a high level of alert and be prepared for the virus because its global pandemic potential still is unknown.

The Center for Infectious Disease Research and Policy (CIDRAP) at the University of Minnesota, Minneapolis, reported that as of May 15(www.cidrap.umn.edu), 131 lab-confirmed cases have been reported, including 36 deaths. Although the number of new H7N9 infections hasn't increased, the death toll is rising as previously confirmed patients remain hospitalized, battling complications that include acute respiratory distress syndrome and organ failure.

Story Highlights

  • The number of reported cases of human infection from the avian influenza A (H7N9) virus in China has dropped off, but according to the CDC, a pandemic threat remains.
  • The United States currently is better prepared than any other country to respond to such a pandemic from a vaccine standpoint, but the H7N9 vaccines in the works face significant challenges in both availability and effectiveness.
  • If H7N9 does become a pandemic, people 65 or older may be at the highest risk.

According to the CDC, the drop-off in newly reported H7N9 cases may be the result of Chinese containment measures, changing seasons or a combination of both. Considering what the CDC learned from the influenza A (H5N1) pandemic, the agency has stated that H7N9 infections -- in birds and people -- may pick up again when the weather turns cooler. There still is no evidence of sustained person-to-person spread, and no cases have been reported outside China.

The CDC is asking physicians to consider the possibility of H7N9 infection in people who present with acute febrile respiratory illness and an appropriate recent travel or exposure history(www.cdc.gov). The agency is recommending that

  • patients with confirmed or probable H7N9, as well as those in whom illness remains under investigation, receive antiviral treatment with a neuraminidase inhibitor as early as possible in the disease course, even if it is more than 48 hours after onset of illness and/or for apparently uncomplicated illness;
  • laboratory testing and initiation of antiviral treatment occur simultaneously; and
  • health professionals reference Antiviral Drugs: Dosage (ACIP)(www.cdc.gov) for additional guidance on the use of influenza antiviral agents, including dosage recommendations for treatment by age group.

Still a Threat

Although the risk for H7N9 infection in the United States remains low, the virus still poses a considerable pandemic threat, so the CDC -- along with the World Health Organization (WHO) -- has been working since mid-April to develop candidate vaccine viruses from two different H7N9 isolates.

According to CIDRAP Director Michael Osterholm, Ph.D., M.P.H., the United States currently is better prepared than any other country to respond to such a pandemic from a vaccine standpoint. But even so, he told AAFP News Now, the H7N9 vaccines in the works face significant challenges(jama.jamanetwork.com) in both availability and effectiveness of the final formula.

CDC Already Taking Precautions Against H7N9

According to the CDC, selected laboratories have been using two different avian influenza A (H7N9) strains to

  • develop a test kit for detecting H7N9 infections in humans that is being shared with approved public health laboratories and distributed to most U.S. states and some international locations;
  • test for the presence of antibodies against the H7N9 virus in human blood samples;
  • test to see if existing antiviral drugs, such as oseltamivir (Tamiflu) and zanamivir (Relenza), are effective in treating H7N9; and
  • develop a candidate vaccine virus that could be used to make a vaccine if it is needed.

The CDC currently is not recommending that travel to China be restricted. Instead, the agency recommends that travelers to China practice hand hygiene, follow food safety practices (including eating only meats and poultry products, including eggs, that have been cooked thoroughly), and avoid contact with animals.

If a case were to be detected in the United States, the CDC indicates(www.cdc.gov) that it would not signal an increase in the potential risk to the public's health unless the transmission pattern of the virus changed. Any such case will be "isolated and cared for. In addition, a contact investigation will be done with people who may have been exposed to the sick person."

"For the family physician, the bottom line message is that vaccines for (seasonal) influenza and H7N9 will likely have some impact in the United States, but it could be extremely limited," said Osterholm. "If you look at the 1957, 1968 and 2009 pandemics, it was always too little, too late."

Osterholm said that there is no reason to believe that an H7N9 vaccine will perform any better than existing seasonal influenza vaccines or the avian influenza A (H1N1) vaccines used in 2009, especially in people ages 65 and older.

"Look at this last year's flu season," he said. "The CDC's own study showed that, for the influenza A vaccine, they could not find protective effectiveness in those persons 65 years of age and older."

Currently, the median age of H7N9 cases in China is 62, said Osterholm.

"We don't know that that will continue to be the median age, but the fact is we cannot show protection for that group," he said. "People say, 'Look at the pandemic vaccine in Europe; with adjuvants, it was 68-70 percent effective,' but all of those studies concentrated on the very young -- children and young adults. So you cannot extrapolate any data from the European vaccine work of 2009 to understand what (a vaccine against this new virus) might do for older people, should H7N9 emerge as a pandemic strain."

Global Challenge

On a global basis, access to any potential H7N9 vaccine will be very limited, and questions regarding its effectiveness will remain, said Osterholm. To protect its own interests, he added, it behooves the United States to help ensure the rest of the world is prepared.

"So many of the products that we use in this country that are critical to our everyday lives -- medications and other things we simply take for granted -- all come from developing countries where the manufacturing is done," Osterholm said. "If anything interrupts international trade and travel, that's going to cause a major crisis for us.

"Supply chains that we normally just think of as being intact won't be, and we already have that problem with generic drugs now, before we even get to the point of a pandemic. How many drugs are in short supply today because some foreign generic manufacturer cannot or does not keep up with demand? That will be magnified with a pandemic."

Osterholm said he and his colleagues have recognized this issue for some time, and there is no short-term solution.

"We need new and better flu vaccines," he said, "ones that can basically be injected days, months or years ahead of a pandemic and still have enough cross-protection to cover many different strains of the influenza virus."

If H7N9 does reach pandemic status, physicians will have to do the best they can with the vaccine supply made available to them and look for other, nonpharmaceutical interventions, as well, Osterholm said.

"By that I mean: How do you do social distancing?" he said. "How do you try to limit transmission between populations? Those are all going to be very real questions."

Osterholm said he thinks a pandemic scenario would quickly evolve into a 'stay tuned' situation, in which the CDC will have to give advice as events unfold.

"For the average family physician, if we have an H7N9 pandemic, it will be unlike any time they've ever known in their clinical practice," he said.