Hong Kong flu of 1968: patterns of an epidemic

The Hong Kong flu of 1968 and later years was the last major virus epidemic in the United States before the ongoing Wuhan virus epidemic, caused by the Covid-2019 virus first described in Wuhan, Hubei, China during late 2019, also known as SARS-CoV-2. The Hong Kong flu caused at least 100,000 fatal illnesses in the United States, among more than one million worldwide.

There are major problems characterizing an epidemic caused by a new virus, even using technology of molecular biology that had not yet been invented when the Hong Kong flu of 1968 struck.
• How reliably do laboratory tests identify and classify infections?
• How large a fraction of the population has been tested for infection?
• What fraction of infections have been missed or misclassified?
How often or seldom do infected people transmit infection?
• How often is death resulting from infection missed or misclassified?
• How long do virus deposits remain infectious in typical environments?
• How much viral dose is needed to cause an infection?
How much individual variation occurs in resistance to infection?
• Can infection and contagion occur without clinical symptoms?
• How much individual variation appears in severity of infection?
• Are infections or severe illness resulting from them seasonal?
• How reliable are antibodies as indicators of prior infections?
• Do infection and recovery confer immunity, or can disease reoccur?

Accurate answers to such questions often take years of research. Without answers, social measures to control an epidemic may misfire: costly but ineffective steps taken or simple and effective steps missed. Medical measures often take years of research as well. Vaccines against virus diseases can be highly effective, but they are usually difficult to develop. The first successful, strategically developed vaccine–against yellow fever–took more than 35 years after the classificatiobn of yellow fever as a viral disease in 1901. About 35 years after identification of HIV as the virus causing AIDS in 1985, there is still no safe and effective vaccine licensed by the U.S. government.

Contemporary news: Although the Hong Kong flu turned out to be about as deadly in the United States as the Wuhan virus is often predicted to become, in 1968 the Hong Kong flu did not draw a comparable public response. Writing in the New York Times, Jane E. Brody–then and now a featured writer on personal health–reported in 1968 that “Hong Kong flu gained a foothold…last week. To date, 28 states have reported attacks….” She did not cite case counts or express alarm. Currently Mrs. Brody, now a mother of two and a grandmother, is counseling readers about “managing coronavirus fears” although competing for today’s readers with thousands of other news writers who are stimulating fears. In 2020, she writes, “…it’s the bad news that gets the most attention….”

As Times reporter Brody noted in late 1968, U.S. labs produced about 5 million doses of a late-season vaccine for seasonal flu incorporating activity against the Hong Kong flu. Such a vaccine was possible because of more than 30 years of U.S. experience producing, testing and using flu vaccines. Around 1970, the United States typically produced about 30 million doses of flu vaccine per year, versus about 150 million doses per year recently. There is no comparable experience producing vaccines against a coronavirus, so that recent efforts toward such a vaccine start with a largely blank slate.

Following the patterns of other influenza strains, Hong Kong flu epidemics starting in 1968 and 1969 were seasonal: beginning in late fall and ending before the start of spring. The chart shows deaths in thousands per month from Hong Kong flu during its first two seasons in the United States.

Hong Kong flu deaths, U.S. 1968 and 1969 seasons

HongKongFlu1968-1969SeasonsUnitedStates

Source: Viboud et al., 2005

So far, disease caused by the Covid-2019 virus does not clearly appear seasonal, although the less than four months experience is too limited to be sure of that. In the United States, counts of cases were still rising in most places though the middle of April, 2020, when all records of the Hong Kong flu in the northern hemisphere show cases beginning to fall no later than February.

Contrasts: While the Wuhan virus epidemic seems to be following a similar pattern of surges and responses to controls worldwide, the Hong Kong flu did not. As Viboud and colleagues documented in 2005, Hong Kong flu epidemics followed different patterns in North America and in Europe and the Far East. In North America the first season was the stronger, while elsewhere the second season dominated. A factor these authors did not consider was U.S. vaccines targeting Hong Kong flu. It looks highly unlikely that vaccines targeting the Covid-2019 virus will be produced in time to arrest the first epidemics outside China, still accelerating as of mid-April, 2020. More likely, these epidemics will be controlled by social measures and by intensive testing to identify contagious carriers.

– Craig Bolon, Brookline, MA, April 15, 2020


Marc Lipsitch, Who is immune to the Covid-2019 virus?, New York Times, April 13, 2020

Jane E. Brody, Managing coronavirus fears, New York Times,April 13, 2020

Gina Kolata, Why are some people so much more infectious than others?, New York Times, April 12, 2020

Matthew Perrone, Fears of ‘Wild West’ as Covid-2019 blood tests hit the market, Associated Press, April 12, 2020

Christopher Murray, Forecasting Covid-2019 impact on hospital bed-days, ICU-days, ventilator days and deaths by U.S. state in the next four months, Medrxiv (Cold Spring Harbor Laboratory), submitted March 26, 2020

Xinguang Chen and Bin Yu, Coronavirus disease epidemic in China: real-time surveillance and evaluation with a second derivative model, Global Health Research and Policy 5(7), March 7, 2020

Seasonal influenza vaccine supply for the U.S. 2019-2020 influenza season, U.S. Centers for Disease Control and Prevention, September 24, 2019

Douglas Jordan, Terrence Tumpey and Barbara Jester, Discovery and reconstruction of the 1918 pandemic virus, U.S. Centers for Disease Control and Prevention, December 17, 2019

Timeline of HIV and AIDS, U.S. Department of Health and Human Services, 2019

I. Barberis, P. Myles, S.K. Ault, N.L. Bragazzi and M. Martini, History and evolution of influenza control through vaccination: from the first monovalent vaccine to universal vaccines, Journal of Preventative Medicine and Hygeine 57(3):E115-E120, 2016

Errling Norby, Yellow fever and Max Theiler: the only Nobel Prize for a virus vaccine, Journal of Experimental Medicine 204(12):2779-2784, 2007

Cecile Viboud, Rebecca F. Grais, Bernard A. P. Lafont, Mark A. Miller and Lone Simonsen, Multinational impact of the 1968 Hong Kong influenza pandemic: evidence for a smoldering pandemic, Journal of Infectious Diseases 192(2):233-248, 2005

Jane E. Brody, Hong Kong flu attacks thousands here swiftly, New York Times, December 11, 1968

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