Chemoprophylaxis In Varicella Contact

” What to do when i am exposed to a varicella (chicken pox)during the infective period?".

One topic debated much today was about the efficiency of acyclovir as a chemoprophylactic agent in immunocompetent persons.
All of us know there is a effective, safe time tested vaccine against varicella.Only problem with this is the cost, Need two doses and cost two thousand rupees for a dose .
So even though this is relevant for prevention, a country like ours can not afford. Ideally all of us should get immunized against ie primary prvention.
In that case the above question does nt occur.

still there is answer to the above question

Vaccination even after exposure (post exposure vaccination ) is effective in varicella.This is possible because the incubation period of this illness is long enough ie two to three weeks. If we give vaccine early after contact protecive level of immunity can be raised before the actual virus produce the illness. So the illness may not occur at all or occur in a mild modified manner

OH, all that was about prevention.

What if we develop the illness, chicken pox ?

An effective drug - acyclovir, is available for the last three decades which again is safe time tested drug used for treatment of varicella.
Earlier we were not giving this drug to varicella cases in normal persons. It was reserved to immuno deficient people only .
But now we take a liberal stand, we give acyclovir oral in not sick cases and parenteral in cases with complications.

Now comes the question

"Sir you said vaccine is effective post exposure stage
We heard giving drugs which are used to treat the illness for prevention also. Many examples, we give erythromycin for prevention of diphtheria, whooping cough. We give doxycycline for leptospirosis. We give oral pencillin for prevention of streptococcal infection in rhumatic fever
So why not we give acyclovir as chemoprophylaxis ?"

Yes this is a very relevant question,
But, we dont see many people using this.
There are only very few studies also, most of them old studies. Most of them not good quality studies.

Why ?

Before we answer this question we need to know a bit about the mechanism of action of the drug. Unlike the drug whiich we mentioned as chemoprophylactiic agents this drug acts in a bit different manner.
In fact the virus of chicken pox is a fool.
There is an enzyme thymidine kinase in the virus which give a phosphorus to the acyclovir molecule to make it acyclovir -monophosphate. (that is virus himself give the gun to shoot him.
Then only the next two steps of phosphorilation happen in our cell to make it the active acyclovir tri -phosphate.

What does that mean

If we give the drug when virus is not there, it circulates in blood , and get excreted in kidney. No use.
In fact the viremia occur by around tenth day of contact. If we give that in the right time it may work, it may modify the outcome.
At the same time there is a proven method, effective, safe vaccine if given early.

So is there any situation where we can give chemoprophylaxis.

Yes.

There are few situations where varicella will be more serious , may cause death and major complications , at the same time we vaccination also is not safe.
Eg primary immunodeficiencies.patients on chemotherapautics, Patients who had bone marrow and organ transplantation. This vaccine is a live attenuated virus. It is not safe to give vaccine in these cases.

So in these situations we chemoprophylaxis is recommended.

In fact chemoprophylaxis in these scenarios is not only for a contact, but for longer duration after transplantation recipients.

In short

1. If you had a contact with varicella case during infective period take vaccine , it ll be very effective if given within 72 hours , but we may give it up to five days as this ll at least modify the illness if not prevent
2. Chemoprophylaxis is recommended in immunocompromised situations.
3. No harm in using as chemoprophylaxis, but dont rely on it.
4. A decision to take chemoprophylaxis instead of vaccine is foolish.