Chickenpox (varicella) is a viral infection that causes a widespread itchy rash and fever. Although it is usually an uncomfortable but mild illness, serious complications can occur including bacterial skin infections, pneumonia, and infections of the central nervous system. The chickenpox virus is very contagious and is transmitted from one person to the another by sneezing, coughing, and handling shared objects. Usually once one household member gets sick, the others who have not previously had the disease catch it as well. But it can take from 10 to 21 days for a person to develop symptoms after being exposed. Can taking the chicken pox vaccine during that window of time prevent the disease, or reduce its severity in those who have not been previously vaccinated? Recent research suggests that it can.

Teens and adults often get more serious cases than children, although infants less than one year are also at higher risk. Adults have 10−20 times the risk of complications than children, with pneumonia being the most common. Patients whose immune systems have been suppressed from medications or illnesses can also get dangerously ill. If a pregnant woman catches chickenpox during the first few months she is more likely to have more serious illness and there is a small (1−2%) possibility that the developing fetus can die or the newborn may have birth defects.

Older patients who have not previously been immunized against chickenpox can safely receive the vaccine and two doses, at least one month apart, are recommended for full protection.

In 2005, varicella vaccine was added to the combined vaccine against measles, mumps, and German measles (rubella). The Centers for Disease Control recommend that children receive shots against varicella, when they are 12−15 months old and again when they are 4−6 years old. Older patients who have not previously been immunized against chickenpox can safely receive the vaccine and two doses, at least one month apart, are recommended for full protection.

The study published recently in the January issue of the Pediatric Infectious Disease Journal looked at patients who had been exposed to household members with chickenpox, who had neither the disease nor received a vaccination themselves. Researchers gave subjects the varicella vaccine within five days of their exposure to the sick person, and they followed up one and two months later to see whether or not they had gotten sick. They found that the vaccine was effective in preventing either moderate or severe disease in 79% of the exposed patients. Sixty−two percent of the exposed patients who were immunized did not get sick at all. Although previous studies had suggested an advantage to early immunization, this study did not find a significant difference whether the vaccine was administered three days or between 4−5 days after exposure. Nor did the age of the vaccine recipient appear to influence how effective it was in preventing or lessening disease. The researchers concluded that the vaccines that are currently in use are effective at either reducing the severity or entirely preventing chickenpox if given to a susceptible person within five days of exposure.

There are several take−home messages from this study:

  • Ideally, children should receive all their immunizations on schedule. This not only keeps them healthy but also decreases the potential for spread of diseases among unprotected adults.
  • Once exposure occurs, time is of the essence. It is important to remember that chickenpox is actually being spread before the rash develops and when symptoms are more like a cold. If family members of a patient who has broken out in the chickenpox rash has neither had the disease nor been vaccinated against it, she should contact her doctor immediately and ask whether she would benefit from a varicella vaccination. If there are household members who have serious illnesses, are receiving chemotherapy, or taking high doses of steroids or other drugs that suppress the immune system, they too should contact their doctors. If family members are uncertain about their risk, it's better to check with one's doctor rather than wait and see if they get sick.
  • Because chickenpox is so contagious, recommendations for isolation of the sick patient must be strictly followed. It usually takes at least five days for the rash to become completely crusted over and for a patient no longer to be contagious. Children must not return to school, daycare, or social activities until advised by a physician. Similarly, adults should not return to the workplace until they are no longer contagious.
  • Anyone who is exposed and susceptible should be aware that if they get sick, they will be able to spread the virus to others before they break out in the telltale rash. They must be careful not to be around people who are at high risk from a chickenpox infection for a period from 8 days to 21 days after they themselves were first exposed.

But instead of doing the math yourself, call your doctor.