JAYSHREE

Ph.D SCHOLAR

INFLUENZA AND INFLUENZA

VACCINE

What is influenza?

Influenza, commonly known as “the flu”, is a highly

contagious infection of the airways caused by

influenza viruses.

It is often referred to as “seasonal” influenza

because these viruses circulate annually in the

winter season in the northern hemisphere.

The timing and duration of influenza season varies

-outbreaks can happen as early as October but

most often activity peaks in January or later.

Late season outbreaks occurring in April and even

May have also been reported.

A, B and C influenza viruses

Influenza A and B viruses cause seasonal

epidemics, while type C viruses cause mild

respiratory illness

Influenza A viruses are classified into different strains

or subtypes based on two proteins or antigens on the

virus surface: hemagglutinin (H) and neuraminidase

(N) e.g., H1N1 and H3N2

Influenza B viruses can be classified into two

antigenically distinct lineages, Yamagata and Victoria

like viruses

Influenza A and B strains are included in each year's

influenza vaccine

The vaccine does not protect against influenza C

viruses

Signs and symptoms of

influenza

Sudden onset

Typically starts with a headache, chills and cough,

followed rapidly by fever, loss of appetite, muscle

aches and fatigue, runny nose, sneezing, watery

eyes and throat irritation

Nausea, vomiting and diarrhea may also occur,

especially in children

How is influenza spread?

The virus is spread mainly from person to person

when those with influenza cough or sneeze (droplet

spread)

The droplets are propelled about 3 feet through the

air

People may also become infected by touching an

object or a surface that has the influenza virus on it

and then touching their mouth, eyes or nose

Impact of Influenza-United States,

1990-1999

Approximately 36,000 influenza-associated

deaths during each influenza season

Persons 65 years of age and older account for

more than 90% of deaths

Higher mortality during seasons when influenza

type A (H3N2) viruses predominate

Impact of Influenza-United States,

1990-1999 Highest rates of complications and hospitalization

among young children and person 65 years and older

Average of more than 200,000 influenza-related excess hospitalizations

57% of hospitalizations among persons younger than 65 years of age

Greater number of hospitalizations during type A (H3N2) epidemics

Influenza vaccine development

Each February, the World Health Organization (WHO)

provides a recommendation on the strains to be

included in the influenza vaccine for the northern

hemisphere

Two influenza "A" viruses and one influenza "B" virus

are selected based on the characteristics of the

current circulating influenza virus strains (two "B"

viruses are selected for quadrivalent vaccines)

A new vaccine is reformulated each year to protect

against new influenza infections

Each vaccine lot is tested on healthy individuals to

ensure the vaccine is safe and effective

Influenza vaccine development

(cont’d)

There are currently eight trivalent influenza vaccines

licensed for use in Canada

Seven are trivalent inactivated influenza vaccine

(TIV)

One is a live attenuated influenza vaccine (LAIV)

There are currently three quadrivalent influenza

vaccines licensed for use in Canada

Two are quadrivalent inactivated influenza vaccine

(QIV)

One is a live attenuated influenza vaccine (QLAIV)

For the 2014–2015 influenza immunization program,

Alberta will be using three TIV products and one

QLAIV product

How does inactivated influenza

vaccine work?

Both humoral and cell-mediated responses play a role

in immunity

Administration of inactivated influenza vaccine results

in the production of circulating IgG antibodies to the

viral haemagglutinin as well as a cytotoxic T

lymphocyte response

Humoral antibody levels, which correlate with vaccine

protection, are generally achieved 2 weeks after

immunization and immunity usually lasts less than 1

year

Initial antibody response may be lower in the elderly

and immune.

How does live attenuated influenza

vaccine work?

Immune mechanisms conferring immunity following administration of live attenuated vaccine are not fully understood

Administered by the intranasal route, QLAIV is thought to result in an immune response that mimics that induced by natural infection with wild-type virus, developing both mucosal and systemic immunity

Serum antibodies, mucosal antibodies and influenza-specific T cells may play a role

The viral strains in QLAIV are engineered to be cold adapted (can only replicate in the nasopharynx), temperature sensitive (cannot replicate in the warm temperatures of the lower airways and lungs) and attenuated (unable to cause clinical disease)

Effectiveness of influenza vaccine

Vaccine effectiveness depends on the similarity between

vaccine strains and the strains in circulation during

influenza season

With a good "match," influenza immunization prevents

disease in 70 to 90% of healthy individuals

This drops to 30 to 40% in the frail and elderly

It does, however, prevent death in 85% of the frail and

elderly

It prevents hospitalization in 50 to 60% of individuals

immunized

Even with an imperfect match, Canadian studies show the

vaccine still reduces the overall risk of infection by about

40-60%

A vaccine that is not perfectly matched can still offer

protection against related viruses making illness milder

Vaccine strains for 2014-2015

The strains that will be included in the 2014-2015

influenza vaccine for the Northern hemisphere are:

A/California/7/2009 (H1N1)pdm09-like virus

A/Texas/50/2012 (H3N2)-like virus

B/Massachusetts/2/2012-like virus

B/Brisbane/60/2008-like virus (B/Victoria lineage)

(Quadrivalent QLAIV only)

Facts about trivalent inactivated

influenza vaccine (TIV)

Is an inactivated (killed) vaccine –cannot cause

influenza disease in the vaccine recipient

The virus is grown in hens’ eggs, inactivated, broken

apart and highly purified

In addition to the antigen, the vaccine may contain:

Thimerosal (preservative in multidose vials)

Trace residual amounts of egg proteins,

formaldehyde, kanamycin, neomycin, cetyl trimethyl

ammonium bromide (CTAB), polysorbate 80, sodium

deoxycholate and sucrose

Check the product monograph as ingredients vary

with specific inactivated influenza vaccines

Facts about live attenuated

influenza vaccine (QLAIV)

Is a live vaccine –cannot cause influenza disease in the vaccine recipient because the virus is attenuated or weakened (however is contraindicated in immuno compromised individuals)

The virus is grown in specific pathogen-free eggs from specific pathogen-free chicken flocks

In addition to the antigen, the vaccine may contain:

Trace residual amount of arginine, gelatin hydrolysate (porcine type A), gentamicin, monosodium glutamate, ovalbumin and sucrose

Check the product monograph for other product excipients

Influenza vaccine dosing for specific

ages

6 months up to & including 8 years of age

2 doses

* if never been previously immunized with seasonal influenza vaccine (spaced 4 weeks apart –minimum interval)

1 dose only if previously immunized with seasonal influenza vaccine

9 years of age and older

1 dose

*This recommendation applies whether or not the child received monovalent pH1N1 vaccine in 2009-2010.

Reactions to inactivated influenza

vaccine

The majority of people do not have a reaction to TIV;

however some reactions that may occur are outlined

below. These reactions generally start 6 to 12 hours

after immunization and can last for 1 to 2 days

Common Reactions

Injection site redness, swelling, pain

Fatigue, headache, myalgia

Arthralgia, fever, chills, malaise

Reactions to live attenuated

influenza vaccine Most people have no reaction to QLAIV. If reactions

occur they tend to be mild and last for 1-3 days,

peaking 2 days following immunization.

Common Reactions

Runny, stuffy nose in children and adults

Children –decreased appetite, headache, weakness

and fever

Adults –sore throat, headache, cough and weakness

For children requiring two doses of vaccine, the

symptoms tend to be less frequent following the

second dose.