The 1918 pandemic is the reference point for measuring pandemic threats because it killed so many people world-wide, devastating the young adult population.

The history of pandemics looks like this, according to Flu.gov. This is the U.S. government’s website for public information about the pandemic, including information from many federal agencies.

“History suggests that influenza pandemics have probably happened during at least the last four centuries. Since 1900, three pandemics and several “pandemic threats” have occurred.

1918: Spanish Flu:

“The Spanish Influenza pandemic is the catastrophe against which all modern pandemics are measured. It is estimated that approximately 20 to 40 percent of the worldwide population became ill and that over 50 million people died. Between September 1918 and April 1919, approximately 675,000 deaths from the flu occurred in the U.S. alone. Many people died from this very quickly. Some people who felt well in the morning became sick by noon, and were dead by nightfall. Those who did not succumb to the disease within the first few days often died of complications from the flu (such as pneumonia) caused by bacteria.

“One of the most unusual aspects of the Spanish flu was its ability to kill young adults. The reasons for this remain uncertain. With the Spanish flu, mortality rates were high among healthy adults as well as the usual high-risk groups. The attack rate and mortality was highest among adults 20 to 50 years old. The severity of that virus has not been seen again.

1957: Asian Flu

“In February 1957, the Asian influenza pandemic was first identified in the Far East. Immunity to this strain was rare in people less than 65 years of age, and a pandemic was predicted. In preparation, vaccine production began in late May 1957, and health officials increased surveillance for flu outbreaks.

“Unlike the virus that caused the 1918 pandemic, the 1957 pandemic virus was quickly identified, due to advances in scientific technology. Vaccine was available in limited supply by August 1957. The virus came to the U.S. quietly, with a series of small outbreaks over the summer of 1957. When U.S. children went back to school in the fall, they spread the disease in classrooms and brought it home to their families. Infection rates were highest among school children, young adults, and pregnant women in October 1957. Most influenza-and pneumonia-related deaths occurred between September 1957 and March 1958. The elderly had the highest rates of death.

“By December 1957, the worst seemed to be over. However, during January and February 1958, there was another wave of illness among the elderly. This is an example of the potential “second wave” of infections that can develop during a pandemic. The disease infects one group of people first, infections appear to decrease and then infections increase in a different part of the population. Although the Asian flu pandemic was not as devastating as the Spanish flu, about 69,800 people in the U.S. died.

1968: Hong Kong Flu

“In early 1968, the Hong Kong influenza pandemic was first detected in Hong Kong. The first cases in the U.S. were detected as early as September of that year, but illness did not become widespread in the U.S. until December. Deaths from this virus peaked in December 1968 and January 1969. Those over the age of 65 were most likely to die. The same virus returned in 1970 and 1972. The number of deaths between September 1968 and March 1969 for this pandemic was 33,800, making it the mildest pandemic in the 20th century.

“There could be several reasons why fewer people in the U.S. died due to this virus. First, the Hong Kong flu virus was similar in some ways to the Asian flu virus that circulated between 1957 and 1968. Earlier infections by the Asian flu virus might have provided some immunity against the Hong Kong flu virus that may have helped to reduce the severity of illness during the Hong Kong pandemic. Second, instead of peaking in September or October, like pandemic influenza had in the previous two pandemics, this pandemic did not gain momentum until near the school holidays in December. Since children were at home and did not infect one another at school, the rate of influenza illness among schoolchildren and their families declined. Third, improved medical care and antibiotics that are more effective for secondary bacterial infections were available for those who became ill.”

What Next?

As this history of pandemics shows, there is science and art in managing pandemics, bearing in mind that many factors influence a strain’s spread—-such as the one in 1968 which peaked when school-children were out for holidays and therefore were not bringing it home to their families.

The science and art in this one will be figuring out, as best anyone can, which age groups are more likely to be affected by the flu strain predominant in the pandemic as we approach fall and winter, a time when seasonal and pandemic strains both are in circulation.

This pandemic may benefit from new technologies, such as emergency cell phone/e-mail alert systems, enabling officials to send advice more quickly, for example. Broadband access to online service is now the majority, making it possible for the U.S. government and governments world-wide in nations where Internet access is available to many, to provide instant information in a way not possible in the past. We don’t know if knowing more, sooner, can help protect people.

We may be about to find out.

A pandemic refers to how widespread the infection is. Yesterday, WHO announced that the pandemic H1N1) flu had been reported in the Pacific, Caribbean, Indian Ocean islands.

Acuity or severity refers to how seriously patients are affected in a pandemic.  There appears to be general agreement that, after a mild spring season, there will be a second round in the fall and winter months and that it will be more severe

What is not yet clear is who is at highest risk: Young adults or older ones.

It is clear that people of any age with underlying, serious medical problems are at higher risk. Many of the reported deaths have been in patients public health officials said had one or more major medical conditions before being infected.

This 2009 pandemic influenza, a combination of human, swine and bird viruses, is a new genetic combination in the history of pandemics. History can offer lessons. History cannot predict the course of the 2009 pandemic.

Work on the seasonal flu and the pandemic flu vaccines is underway in a race to develop and deliver vaccines in time for the fall-winter traditional flu season. It is expected that vaccinations will continue throughout the season. Normally, the emphasis is on getting the flu shots as soon as they are available. How effective these shots are depends on how closely the vaccine matches the strain sickening people.  Scientists have to make a judgment call as to what combination is most likely so vaccine can be produced. The influenza strain can change yet again in between decision time and shot time. This does not mean the shot is not valuable in any event. It does affect how much “coverage” patients get to reduce the likelihood of their getting the flu. In all countries, vaccination is preferred, with anti-viral drugs used to complement the shots.

The CDC has reported that only about 40% of Americans got flu shots last year. The goal this year is about 83%.  In addition to personal protection, the more people who get the shots in a common area, the more protection everyone will have.

Health care workers need to be first on the priority list so that they can be available to care for sick patients.

After that, says this new study, public health officials will need to set priorities for vaccinations based on whether this strain looks more like 1918 or 1969 to them.

Medpage Today

“If the current pandemic H1N1 flu acts like the 1918 pandemic, treatment with antiviral drugs should be aimed mainly at adults younger than 65, Italian researchers said.

On the other hand, if the expected fall wave of the H1N1 pandemic behaves like the flu seen in “1969 and 1970, those over 65 should get treatment priority, according to Stefano Merler, PhD, of the Bruno Kessler Foundation in Trento, Italy, and colleagues.

“Depending on how the flu acts in the fall, those scenarios would save lives, although they would have little effect on the clinical attack rate, or the needed stockpile of medications, Dr. Merler and colleagues said online in BMC Infectious Diseases.”

Source: Flu.gov, History of Pandemics

Source: Medpage Today, July 28, 2009

Citation: BMC Infectious Diseases 2009; DOI: 10.1186/1471-2334-9-117.