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.
1976:
Swine Flu Scare
When a novel virus was first identified at Fort Dix, it was labeled
the "killer flu." Experts were extremely concerned because
the virus was thought to be related to the Spanish flu virus of
1918. The concern that a major pandemic could sweep across the
world led to a mass vaccination campaign in the United States.
In fact, the virus--later named "swine flu"--never moved
outside the Fort Dix area. Research on the virus later showed
that if it had spread, it would probably have been much less deadly
than the Spanish flu.
1977:
Russian Flu Scare
In May 1977, influenza A/H1N1 viruses isolated in northern China,
spread rapidly, and caused epidemic disease in children and young
adults (< 23 years) worldwide. The 1977 virus was similar to
other A/H1N1 viruses that had circulated prior to 1957. (In 1957,
the A/H1N1 virus was replaced by the new A/H2N2 viruses). Because
of the timing of the appearance of these viruses, persons born
before 1957 were likely to have been exposed to A/H1N1 viruses
and to have developed immunity against A/H1N1 viruses. Therefore,
when the A/H1N1 reappeared in 1977, many people over the age of
23 had some protection against the virus and it was primarily
younger people who became ill from A/H1N1 infections. By January
1978, the virus had spread around the world, including the United
States. Because illness occurred primarily in children, this event
was not considered a true pandemic. Vaccine containing this virus
was not produced in time for the 1977-78 season, but the virus
was included in the 1978-79 vaccine.
1997:
Avian Flu Scare
The most recent pandemic "scares" occurred in 1997 and
1999. In 1997, at least a few hundred people became infected with
the avian A/H5N1 flu virus in Hong Kong and 18 people were hospitalized.
Six of the hospitalized persons died. This virus was different
because it moved directly from chickens to people, rather than
having been altered by infecting pigs as an intermediate host.
In addition, many of the most severe illnesses occurred in young
adults similar to illnesses caused by the 1918 Spanish flu virus.
To prevent the spread of this virus, all chickens (approximately
1.5 million) in Hong Kong were slaughtered. The avian flu did
not easily spread from one person to another, and after the poultry
slaughter, no new human infections were found.
In
1999, another novel avian flu virus – A/H9N2 – was found that
caused illnesses in two children in Hong Kong. Although both of
these viruses have not gone on to start pandemics, their continued
presence in birds, their ability to infect humans, and the ability
of influenza viruses to change and become more transmissible among
people is an ongoing concern.