The Chinese government has withheld samples of a virulent strain of avian flu from American researchers for over a year, the New York Times reports. And this strain of flu prevalent in birds, called H7N9, is particularly fatal, killing 40% of people who contract it. However, so far, it hasn’t spread readily from fowl to humans, affecting largely only people who work with live poultry, and even then just a small percentage relative to the number of infected birds. Human-to-human spread if this bird flu has also been extremely small, but Americans have essentially no immunity to the strain and seasonal vaccines would have no effect.
Researchers need access to samples taken from rapid, deadly, and unique outbreaks to study mutations to better understand the strain, and to formulate or be prepared to formulate vaccines against it. Researchers want to study H7N9 as closely as possible due to the risk of mutation. Individual strains of influenza quickly mutate to become more deadly and transmissible, and new strains emerge unpredictably.
The alleged refusal of China to provide samples for over a year has baffled and infuriated experts who spoke to the New York Times. The transfer of samples typically takes months and relies on World Health Organization (WHO) rules. The holdup may be tied to the trade war started by the Trump administration, which has imposed waves of tariffs against China.
A CDC spokesperson rebutted the Times article in part, however, in a statement to Fortune. “CDC has received a majority of the Influenza A H7N9 virus samples we have requested from China. In addition, Chinese researchers have consistently shared clinical and epidemiological data on H7N9 infections occurring in China,” the spokesperson said, as well as researchers sharing genetic sequences via an international program. The spokesperson called CDC’s partnership with China “strong and collaborative.” The Times article notes, citing anonymous sources, that a small set of samples from Taiwan and Hong Kong were provided to four research institutions, but that the CDC was waiting on several more.
A mutated H7N9 that leapt to humans easily and spread rapidly among people could lead to a global pandemic. Previous flu pandemics have killed hundreds of thousands to tens of millions of people, and led to millions or more hospitalizations. During the 1918-1919 “Spanish influenza” pandemic, around 50 million people died globally. While judged the worst in recorded history, there’s no consensus of how to blunt a similar new strain today. The more recent H1N1 pandemic in 2009 killed between 151,700 and 575,400 people worldwide, according to the Centers for Disease Control (CDC).
Nearly 1,600 people are known to have been infected across six epidemics in China from H7N9 when it emerged in 2013, although half were in the 2016-2017 flu season. Since October 1, 2017, the CDC says only a single case has appeared. The Chinese government claims to have eradicated the disease from fowl through a single vaccination campaign. The strain isn’t lethal to birds.
As many as 646,000 people die annually around the world from seasonal flus, outside of non-seasonal pandemics. Vaccines reduce the risk of flu by 40% to 60% in the general population in seasons when the vaccines closely match prevalent strains of influenza. It especially effective in reducing children dying from flu-related causes. The vaccines currently have to be manufactured months before flu season becomes, and manufacturers rely on outbreaks else in the world as one predictor.
During the 2017-2018 flu season, a 50-year-old strain, H3N2, appeared in a new virulent form against which the seasonal vaccine proved substantially less effective than in typical years—as little as 10% effective in some countries. This led to the most pediatric deaths (179) and the highest rate of hospitalization for pneumonia and secondary infections in the last decade—about 500 hospitalizations per 100,000 people, almost 50% higher than the most recent worst season, 2014-2015. (Adult fatalities are recorded differently than those of children, and an approximate count emerges long after each season is over.)
The Chinese Center For Disease Control and Prevention website appears to be offline at this writing, and Fortune was unable to request comment.
This article was updated with a comment from the CDC.