Pandemic influenza history

Pandemics over the last hundred years:

1. Pandemic (H1N1) 2009 Influenza, 2009–2010
2. Hong Kong influenza, 1968–69
3. Asian influenza, 1957–58
4. Spanish influenza, 1918–19

The Spanish influenza killed an estimated 30,000 to 50,000 people in Canada, and 20 to 40 million people worldwide. During the Spanish influenza the greatest number of deaths occurred in those 20–40 years old. In contrast, during the Asian and Hong Kong pandemics, the greatest death rates occurred in people less than 60 years old. 

2009: Pandemic (H1N1) 2009 Influenza

On June 11, 2009, in response to the global spread of a new strain of influenza, the World Health Organization (WHO) declared the outbreak to be an influenza pandemic, the first since 1968.

Officials believed the outbreak began in Mexico in March 2009, or earlier. The then called “H1N1 swine flu” was first identified in California in late April 2009. Health officials quickly linked the new virus to the outbreak in Mexico.

In Alberta, the pandemic occurred in two waves. The first wave peaked in June 2009, the second in October 2009. Overall, younger people were more at risk to get the virus, but with less severe symptoms compared to the seasonal influenza virus strains seen each year. Illness among school-aged children (aged 5–18 years) was particularly high.

The WHO declared the H1N1 pandemic over on August 10, 2010.

• Read more Pandemic (H1N1) 2009 history

1968: Hong Kong Influenza

In early 1968, the influenza pandemic was first detected in Hong Kong. The first cases in North America were detected in the United States in September of that year, but illness did not become widespread 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. This was the mildest pandemic in the 20th century.

There could be several reasons why fewer people died due to this virus –

1. The Hong Kong influenza virus was similar in some ways to the Asian influenza virus that circulated between 1957 and 1968. Earlier infections by the Asian influenza virus might have provided some immunity against the Hong Kong influenza virus.
2. The 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.
3. Improved medical care and antibiotics that are more effective for secondary bacterial infections were available for those who became ill.

1957: Asian Influenza

In February 1957, an influenza strain was identified in Asia that people less than 65 years of age were not immune to, and a pandemic was predicted. In preparation, vaccine production began in late May 1957, and health officials increased surveillance for influenza outbreaks.

Unlike the virus that caused the 1918 pandemic, the 1957 pandemic virus was quickly identified due to advances in scientific technology.

In October 1957, infection rates were highest among school children, young adults, and pregnant women. 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 in the United States, 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.

1918: Spanish Influenza

The Spanish influenza pandemic is the catastrophe against which all modern pandemics are measured. It was named the Spanish influenza because Spain was the first country to report a serious outbreak of the disease, with nearly 8 million killed by May 1918.

It is estimated that approximately 20–40 per cent of the worldwide population became ill and more than 20 million people died. 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 influenza (such as pneumonia) caused by bacteria.

One of the most unusual aspects of the Spanish influenza was its ability to kill young adults. The reasons for this remain uncertain. With the Spanish influenza, mortality rates were high among healthy adults as well as the usual high-risk groups. Mortality was highest among adults 20–40 years old. The severity of that virus has not been seen again.