Influenza Epidemiology

Question 1

when are epidemics seen?

Answer 1

Winter epidemics

in the tropics it may be less seasonal or higher prevalence in the rainy season

Question 2

what are epidemics seen in association with?

Answer 2

minor mutations in the surface proteins of the virus

Question 3

what is this minor mutation known as?

Answer 3

antigenic drift

Question 4

what causes a pandemic ?

Answer 4

Influenza A

they are rare and unpredictable

Question 5

what happens to the influenza aA and how

Answer 5

influenza A have a segmented genome and get antigenic shift

Question 6

what is antigenic drift?

Answer 6

changes in the principal surface antigens of influenza A - haemagglutinin and neuramidase - make these viruses antigenically labile

Minor changes described as antigenic drift occur progressively from season to season.

Question 7

when does antigenic shift occur?

Answer 7

periodically, resulting in major changes and the emergence of a new subtype with a different haemagglutinin protein

Question 8

why is it such a panic when there is antigenic shift?

Answer 8

Because immunity from the previous virus may not protect completely against the new subtype, the population may have little or no immunity, and this may therefore lead to widespread epidemics or even a pandemic.

Question 9

give an example of the process of antigenic shift?

Answer 9

human is infected by a human adapted flu A and a duck is infected with a duck adapted flu A

imagine both of these viruses simultaneously infect another animal- the mixing vessel . This could also be a human

The gene segments will be shuffled together and potentially something new to nature will be created

If a farmer gets infected he will not have any immunity because of the envelope proteins from the duck genes

Question 10

how is flu prevented?

Answer 10

killed vaccine and live attenuated vaccine

Question 11

how is a killed virus generateD>

Answer 11

Virus grown in hen’s eggs or cell culture then inactivated and combined with an adjuvant

Question 12

what is contained in killed vaccines >

Answer 12

currently contains 2 different influenza A viruses and one influenza B virus

Question 13

how often and who is it given to?

Answer 13

given annually to adult patients at risk of complications

given to health care workers

Given to children aged 6 months to 2 years at risk of complication

Question 14

who is offered the live vaccine?

Answer 14

Offered this year to ALL children aged 2-5, and all primary school children

Question 15

For which age group is the live attenuated more effective

Answer 15

More effective than killed vaccine in children aged 2-17

Question 16

how is live vaccine administered?

Answer 16

intra-nasally

Question 17

what is protective efficacy dependent on?

Answer 17

depends on the match of vaccine to the circulating virus and on patient group, but is never better than 70% effective in preventing clinical infection

Question 18

when are antivirals used as prophylaxis ?

Answer 18

after contact with flu

rarely used but might be used in care homes and boarding school