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4 short notes commonly asked in Community Medicine (PSM) theory paper, answered!! (9th June 2016)

Today’s 4 short notes: 9th Jun 2016
Net Reproduction Rate (NRR)
Hepatitis B Vaccine
Pearl Index

It is a concept in sociology.
Acculturation refers to changes that take place as a result of contact with culturally dissimilar people, groups, and social influences.
When there is contact between two people with different types of culture, there is diffusion of culture both ways. There are various ways by which culture contact takes place. Some of them are:
Trade and commerce
Propagation of religion
The radio, the television, the cinema have been important factors in shaping the cultural behaviour patterns of people

It is because of culture contact and can be both good and bad.
The British brought their culture into India through conquest and Indians are said to be the next best English men
The introduction of scientific medicine is through culture contact.
The change in food habits of people is brought about through culture contact. Many orthodox Brahmins in India today eat meat.
The widespread use of tobacco all over the world is because of culture contact.

Net Reproduction Rate (NRR)
NRR is a fertility related statistic. It is a demographic indicator.
NRR is defined as ‘’the no. of daughters, a new born girl will bear during her lifetime, assuming fixed age specific fertility and mortality rates’’.
NRR of 1 is equivalent to attaining the two child norm. If the NRR is less than one, then the reproductive performance of the population is said to be below replacement level.

Pearl Index
Pearl Index is used in evaluation of contraceptive methods.
Contraceptive efficacy is generally assessed by measuring the no. of unplanned pregnancies that occur during a specified period of exposure and use of the contraceptive method.
Two methods that have been used to measure contraceptive methods are:
The Pearl Index and
Life table analysis
The pearl index is defined as: ‘’the no. of failures per 100 women years of exposure (HWY)’’.
This rate is calculated by the following formula:

Failure rate per HWY=(total accidental pregnancies )/(total months of exposure) X 1200
The total accidental pregnancies shown in the numerator must include every known conception whatever its outcome, whether it has terminated as a live birth, still birth or abortion or has yet not terminated.
The factor 1200 is the no. of months in 100 years.
The total months of exposure in the denominator is obtained AFTER deducting
10 months for a full term pregnancy and
4 months for an abortion.
A failure rate of 10 per HWY would mean that in a lifetime of an average woman, 2.5 accidental pregnancies would result, since the average fertile period of a woman is about 25 years.
In defining and interpreting a use effectiveness trial, a minimum of 600 months of exposure is usually considered necessary before any firm conclusion can be reached.
Limitation of Pearl Index: With most methods of contraception, failure rates decline with duration of use. The pearl index is based on a specific exposure, usually one year and therefore fails to accurately compare the contraceptive methods at various durations of exposure. This limitation is overcome by using the method of Life Table Analysis

Hepatitis B Vaccine
The active substance in recombinant Hepatitis B vaccine is HBs Antigen.
HBV is available as monovalent formulation or in fixed dose combination with other vaccines including DPT, HIB, Hepatitis A and inactivated Polio vaccine
When immunizing against HBV at birth, only monovalent Hepatitis B vaccine should be used.
The dose for adults is 10 to 20 micrograms at 0, 1 and 6 months. Children below 10 yr. of age should be given half of the adult dose at 0, 1 and 6 months.
Route of Administration: Intra Muscular
Site of injection: The greatest reliability of absorption is ensured by injecting into the deltoid muscle. For infants and children less than 2 yr. anterolateral aspect of the thigh is used as the vaccination site. Intradermal administration of the vaccine is NOT recommended because the immune response is less reliable particularly in children.
The HB vaccine does not interfere with immune response to any other vaccine and vice versa.
The birth dose of HB vaccine can be given safely together with BCG. However, the vaccines should be given at different sites.
Schedule for vaccination can be divided into those that include a birth dose and those that do not.
Schedule including birth dose:
Recommended is first dose at birth followed by second and third dose at time of the first and third dose of DPT vaccination respectively.
Alternatively a 4 dose schedule may be used as is used in India: The dose at birth is followed by 3 additional doses at 6, 10 and 14 weeks with DPT vaccination.
The doses following the birth dose may be given either as monovalent vaccine or as a combination e.g. with DPT and/or HIB, as per the schedules commonly used for these vaccines. The minimum recommended interval between the doses is 4 weeks.
These schedules will prevent most peri-nataly acquired infections. In countries where a higher proportion of Hepatitis B virus infection is acquired perinataly, specifically in countries where the chronic HBV infection prevalence is more than 8% in the general population, the first dose of HB vaccination should be given within 24 hours of birth to prevent perinatal transmission.
The complete vaccine series induces protective antibodies levels in > 90% of infants, children and young adults. This keeps on decreasing with increasing age. The duration of protection is at least 15 yr. and perhaps lifelong.
Some infants born prematurely with low birth weight (<2Kg) may not respond well to vaccination at birth. However by 1 month of chronological age, all premature infants regardless of initial birth weight or gestational age respond adequately. In such cases, the vaccine dose given at birth should not be counted towards the primary series, and 3 additional doses should be given according to National immunization schedule.
Immunosuppressive illnesses such as advanced HIV infection, chronic liver disease, chronic renal failure and diabetes are associated reduced immunogenicity of the vaccine. If the primary series is interrupted after the first dose, the second dose should be administered as soon as possible, and a second and third dose separated by a minimum interval of 4 weeks. If only the third dose is delayed, it should be administered as soon as possible.
Immunization in adults:
Routine pre – exposure vaccination should be considered for high risk groups.
Adults 20 yr. of age and older, should receive 1 ml of adult formulation.
The usual schedule for adults is 3 doses, first and second doses should be separated by AT LEAST 4 weeks and a third dose 4 to 6 months after the second dose.
If an accelerated schedule is needed, the minimum interval between the first dose and second dose is 4 weeks and between the second and third dose is 8 weeks. However the first and third dose should be separated by no less than 16 weeks.
Interruption in the vaccine schedule does not require restarting of the vaccine series.
The high risk persons for whom the vaccination is recommended are
Persons with high risk sexual behaviour
Partners and household contacts of HBs antigen positive persons
Injecting drug users
Persons who frequently require blood or blood products
Recipients of solid organ transplantations
Those at occupational risk of HB virus infection including healthcare workers
International travellers to HBV endemic countries
HB vaccine is contraindicated for individuals with a history of allergic reaction any of the vaccine components.
Neither pregnancy nor lactation is a contraindication
The vaccine should be stored at 2-8 degree Celsius
Freezing MUST be AVOIDED as it dissociates antigen from alum adjuvant