In April, President Donald Trump suspended U.S. funding for the World Health Organization and declined to support a global initiative at developing a COVID-19 vaccine. At the World Health Assembly held Monday, the United States also refrained from joining 122 countries calling for a "comprehensive evaluation" of the global response to the COVID-19 pandemic and a scientific investigation into the source of the virus. And late Monday night, Trump tweeted a letter he sent to the WHO threatening to make the funding suspension permanent and to reconsider American membership unless the organization committed to "major substantive improvements" in the next 30 days. Such actions are just the latest efforts by Trump's administration to shun traditional alliances and international cooperation in favor of an "America First" foreign policy.

But withdrawing from international engagement might leave the United States more — not less — vulnerable during the current pandemic. Indeed, as scientists and public health experts have long argued, combating pandemics require cooperation and scientific expertise cultivated across borders. As the world demonstrated over 50 years ago as it battled the "Hong Kong Flu," diseases know no borders and demand global responses that focus on cooperation, coordination and communication.

On July 13, 1968, in what was then the British colony of Hong Kong, government clinics reported a sudden upsurge of patients with flu-like symptoms. Within weeks, an influenza outbreak swept the city, and within months, the rest of the world. Scientists later classified the then-novel virus as H3N2, but history has termed it the "Hong Kong Flu." While not as lethal as the infamous 1918-1919 Influenza that killed 50 million worldwide or even the 1957-58 "Asian flu" that killed 1.1 million worldwide, the 1968-69 Hong Kong Flu still killed an estimated 1 million worldwide and infected millions more.

In Hong Kong, where the outbreak was first recorded, roughly 500,000 residents, or 15% of the city's population, became infected. At least here, the mortality rate was low and clinical symptoms like fever, chills, muscle pain and weakness were relatively mild. Nonetheless, the virus was highly contagious, inflicting widespread suffering, especially among front-line workers, and economic damage.

After battering Hong Kong in the sweltering summer, the virus began its relentless march across the globe. It first spread across Asia before penetrating the Iron Curtain in Europe. France estimated 35,000 deaths from the flu. Poland was the hardest hit among all European countries, with up to four million infected.

In the United States, veterans returning from the war in Vietnam in early September reported infections. It then spread to the civilian population in early October and grew exponentially across all 50 states by late December. Schools in at least 23 states closed and the pandemic placed enormous strains on health care and other social services. Small towns like Needles, California, reported influenza symptoms among 40% of the population. In Milwaukee, up to half the adult population did not show up for work in late 1968 at the height of the pandemic. The flu ultimately killed an estimated 100,000. It also stirred xenophobia as pretext for protectionism. In Des Moines, a roadside billboard declared: "Hong Kong Flu is Unamerican! Catch something made in the U.S.A."

Geopolitical divides threatened to exacerbate the global pandemic. In fact, despite its name, the flu originated not in Hong Kong but in China, where intensive farming with poultry and humans living in proximity created conditions that fostered the recombination of avian and human influenza viruses. But since the People's Republic at the time was not recognized as the legitimate government of mainland China by the United Nations and the United States, it was also excluded from the WHO and hence many international reporting networks. Moreover, as the country was in the throes of the Cultural Revolution, political and social upheaval complicated efforts in managing any outbreaks. The only hint that something was afoot came weeks before the early July outbreak when Hong Kong doctors reported flu-like symptoms among travelers returning from China.

Meanwhile, Cold War rivalries emboldened governments to weaponize news of the pandemic for political purposes. In Hong Kong, newspapers breathlessly reported on the ravages throughout the city and eventually around the world. But the slant of their coverage varied depending on which side they took in the ongoing contest between China under Mao Zedong and Taiwan under Chiang Kai-shek.

A pro-Taiwan newspaper reported on the virus's rumored origins in China early in the outbreak even before any official or scientific confirmation. Its pro-China counterpart liberally sprinkled revolutionary quotations from Chairman Mao in a story of convalescing patients and medical workers. When the pandemic finally hit Taiwan in early September, coverage shifted to embarrassing the rival regime by emphasizing how the Taiwanese government was left unprepared as thousands across the island succumbed to the virus with no vaccines or effective treatments. "The bandit Chiang says no way to prevent its outbreak," one headline gleefully blared.

But, scientists across the globe stepped up. In mid-July within two weeks after the first recorded cases, Dr. Wai-Kwan Chang, senior medical officer of the Hong Kong Government Virus Unit at Queen Mary Hospital, isolated and identified the virus strain. Upon discovering it was a novel virus, she sent samples to the World Influenza Centre in London and the International Influenza Center for the Americas in Atlanta. After more testing, both centers in turn distributed them to vaccine producers. By mid-August, the WHO alerted the world by warning of the virus's incipient spread. Quick action led to the development of a vaccine within six months. The first million doses were released in the United States in November 1968 with another nine million by January 1969.

To be effective, however, scientific expertise demanded international cooperation and coordination. Chang was able to act quickly precisely because the WHO designated her laboratory as an influenza center years before to provide up-to-date information as part of its Global Influenza Surveillance Network (GISN). Support for the WHO's program came from the international community, which still remembered the horrors wrought by the 1918-1919 flu. It also came from the United States itself, which realized its own influenza surveillance network was limited in value without any international reach.

While not frictionless, the dissemination of crucial information bridged ideological and geopolitical differences even at the height of the Cold War. The Soviet Union, for instance, received a sample strain of the virus from the World Influenza Centre as well as steady updates tracking its spread. In a report to the WHO on the flu's impact on their country, Soviet scientists concluded by "emphasiz[ing] the usefulness of international collaboration in the study of the epidemiology of influenza."

The Hong Kong Flu returned in subsequent years, but its threat subsided as vaccines became increasingly effective in protection and abundant in supply. Dr. Maurice Hilleman, whose leading efforts at developing the vaccine for the Hong Kong Flu and other diseases earned him the title "father of the modern vaccine," credited early detection by the WHO for success in this effort.

The global history of the Hong Kong Flu shares many parallels with the COVID-19 pandemic today. More importantly, it highlights the many elements of a successful response to a global pandemic. Expertise from scientists like Chang and Hilleman was undoubtedly critical to identifying the novel virus, understanding its epidemiology and developing a vaccine. But so too was the timely circulation of information that facilitated international cooperation and coordination. These lessons remain relevant for dealing with any pandemics, future or current.

Indeed, viruses pay little heed to national borders, national identities or geopolitics in their spread. Any effective response should accordingly embrace solutions that are also international in their scope. International organizations like the WHO have come under fire for being too deferential to their member states' demands. But whatever their merits, such critiques actually underscore the critical role of international cooperation. Global problems like pandemics are simply too important to be subordinated to parochial interests.

Philip Thai is an associate professor of history at Northeastern University and author of "China's War on Smuggling: Law, Economic Life, and the Making of the Modern State, 1842-1965."