"Immunization Schedule" — Practice

Question 1

Which vaccines are given at birth under India's Universal Immunization Programme?

Accepted Answer

A

Question 2

Which is a live attenuated vaccine?

Accepted Answer

C

Question 3

A 14-month-old received only birth doses. What should be done?

Accepted Answer

A

Question 4

Which vaccine is damaged by freezing?

Accepted Answer

C

Question 5

A child sustains a deep dog bite with bleeding. What is required?

Accepted Answer

A

Question 6

Why must two live parenteral vaccines be given either on the same day or at least four weeks apart?

Accepted Answer

Because of interference mediated by the innate immune response. A live vaccine replicates in the recipient, and that replication triggers an interferon response as part of the normal antiviral defence.

Interferon establishes an antiviral state in surrounding cells for a period of days to weeks, and a second live vaccine given during that window replicates less efficiently. Since a live vaccine depends on replication to generate an adequate immune response, the second vaccine may produce a weaker or failed response.

Giving them on the same day avoids the problem entirely, because neither has yet induced the interferon state when the other is administered. Separating them by four weeks allows the response to the first to subside before the second is given.

The rule applies only to parenteral live vaccines. Oral live vaccines such as rotavirus and oral polio vaccine act on the gut mucosa and do not impose the same restriction, and non-live vaccines can be given at any interval.

Question 7

Why should household contacts of a child receiving chemotherapy be vaccinated, and which vaccine must be avoided?

Accepted Answer

Because the child cannot protect themselves. Chemotherapy suppresses the immune system to the point where live vaccines are unsafe and responses to non-live vaccines are poor, so the child is both unprotected and unusually vulnerable to infections that would be trivial in a healthy child.

The only remaining strategy is to remove the sources of exposure, and the commonest source is the household. Vaccinating parents and siblings, particularly against influenza, varicella, measles and pertussis, prevents them acquiring and transmitting these infections. This approach is called cocooning.

The one exception is oral polio vaccine. Because it is live and replicates in the gut, the attenuated virus is shed in stool for several weeks after vaccination, and a household member handling nappies or sharing a bathroom can be infected by that shed virus. In an immunocompromised child, infection with even attenuated poliovirus can cause paralytic disease.

Inactivated polio vaccine is therefore used for household contacts, since it cannot replicate and cannot be shed.

Question 8

A clinic's refrigerator logged minus 1 degree overnight. Vaccine vial monitors on all vials are unchanged. What should be done and why?

Accepted Answer

All adsorbed vaccines in that refrigerator must be discarded, and the unchanged vial monitors provide no reassurance whatsoever.

Vaccine vial monitors are chemical indicators that darken cumulatively in response to heat. They were designed to solve the problem of heat exposure during transport and outreach in hot climates, and they do that well. They are completely insensitive to cold, so a vial that has been frozen solid displays an identical monitor to one stored perfectly.

Freezing damages the aluminium-adsorbed vaccines, meaning hepatitis B, pentavalent and the tetanus toxoids. The antigen is bound to the aluminium adjuvant, and ice crystal formation disrupts that binding irreversibly. The vaccine still looks normal and is still sterile, but its immunogenicity is substantially reduced, so a child receiving it appears vaccinated and is not.

The shake test is the correct tool: a previously frozen adsorbed vaccine forms flakes that sediment rapidly, leaving clear supernatant, whereas an unfrozen control remains uniformly turbid.

This is why freezing is the more dangerous cold chain failure. Heat damage announces itself; cold damage does not.

Question 9

An 8-month-old missed the rotavirus course entirely. Should it be started now?

Accepted Answer

B

Practice — "Immunization Schedule"

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