Influenza viruses belong to the family Orthomyxoviridae and have a single- stranded
segmented RNA genome. Viruses are different from bacteria. While scientists consider
bacteria as a kind of plant, viruses with strictly defined atomic structures, like influenza
virus, which poison the body of the organism they attack, are living organism themselves.
In addition, they can be considered as living body because they can multiply in unlimited
quantities.
The influenza viruses are classified into types A, B, and C on the basis of their core
proteins. Type A viruses are further subdivided according to their envelope glycoproteins
with haemagglutinin (HA) or neuraminidase (NA) activity. Characteristic of many RNA
genome viruses, influenza virus undergoes high mutation rates and frequent genetic
reassortment (combination and rearrangement of genetic material) leading to variability
in HA and NA antigens. Minor changes in the protein structure in influenza A strains
("antigenic drift") occur frequently, enabling the virus to cause repetitive influenza
outbreaks by evading immune recognition. Major changes in the influenza type A HA
antigen ("antigenic shift") are caused by reassortment from different influenza A
subtypes, such as between animal and human subtypes, and in rare events, such shifted
viruses can result in strains capable of causing large regional or global pandemic
outbreaks. Influenza B and C viruses mainly affect humans, whereas influenza A viruses
infect a range of mammalian and avian species. Only type A and B cause human disease
of any concern.
Influenza virus is transmitted primarily by droplets or respiratory secretions of infected
persons. Influenza occurs all over the world, with an annual global attack rate estimated
at 5 – 10% in adults and 20 – 30% in children. Influenza is associated with considerable
economic burden arising from health-care costs, lost days of work or education, and
general social disruption across all age groups. Secondary bacterial pneumonia is a
frequent complication of influenza infection, particularly in elderly people and
individuals with certain chronic diseases, resulting in a significant level of morbidity and
mortality. An influenza pandemic is a rare but recurrent event.
When a person is attacked by influenza virus, his body produces a temporary immunity,
but this protection is against only the type of virus that caused the influenza. Moreover,
this immunity persists for less than a year because a virus changes its characteristics
gradually. Therefore, it is necessary to have a specific vaccine to prevent the spread of
influenza virus.
The World Health Organization reviews the world epidemiological situation twice
annually and if necessary recommends new vaccine strain(s) in accordance with the
available evidence. In general, seasonal influenza vaccines are trivalent, containing a
mixture of influenza A and B strains thought most likely to circulate in the coming season.
Scientists have been developing different kinds of vaccines that have been found to be
from 75% to 90% effective for at least seven months against both A and B types of the
influenza virus, and even the new strains. Furthermore, they recommend that yearly
vaccination is necessary for those at the greatest risk of complications from influenza,
such as pregnant women and the elderly.
1. With what topic is the passage primarily concerned?
A. Immunity to disease
B. The influenza virus
C. Bacteria
2.
3.
4.
5.
6.
7.
8.
9.
D. RNA genome
The word “they” in the passage is closest in meaning to
A. bacteria
B. viruses
C. scientists
D. plant
Why does the author say that viruses are living bodies?
A. They have complicated structures.
B. They are able to poison other living organisms.
C. They are able to multiply.
D. They need to attack living organisms.
How do scientists classify types of viruses?
A. by classifying core viruses’ core protein.
B. by classifying viruses’ structures.
C. by classifying RNA genome
D. by classifying viruses’ activity.
The word “strains” in the passage refers to
A. plant
B. bacteria
C. virus
D. core proteins
According to the passage, how does the body react to the influenza virus?
A. It becomes immune to all types of vaccines.
B. It prevents further infection to other types of the virus.
C. It produces immunity to the type of virus that invaded it.
D. It becomes more susceptible to the type of virus that caused the influenza.
Why does the author mention “a virus changes its characteristics
gradually”?
A. To show the complicated activity of virus can make the disease worse
B. To show the mutation makes the infected body difficult to carry out a
successful immunization program
C. To show vaccines are ineffective against virus
D. To show virus can spread quickly
The word “recurrent” refers to
A. periodical
B. quick
C. regional
D. serious
It can be inferred from the passage that
A. Scientists carry out continuous research to figure out vaccines for influenza.
B. There are no effective vaccines against newly evolving strains.
10.
C. Vaccines are used widely to avoid influenza pandemic.
D. Scientists stopped studying influenza virus.
The tone of passage can be best described as
A. objective
B. persuasive
C. informative
D. narrative