Varicella Vaccine: An Expert Interview
As one of the newer vaccines, Varicella still inspires questions in patients and providers alike. In a recent interview, Kathleen Neuzil, MD, MPH, member of the Adult Immunization Initiative Physician Advisory Board, the ACP-ASIM representative to the CDC's Advisory Committee on Immunization Practices, and contributor to the upcoming edition of the Guide to Adult Immunization, addressed some of these questions.
To start with, who should get the varicella vaccine?
Dr. Neuzil: Adolescents and adults who did not receive the vaccine as a child and never had a case of chickenpox should receive two doses of varicella vaccine 4-8 weeks apart - but when you're looking at a patient, what you should be thinking is, "Is this patient at high risk of exposure or at high risk for complications from chickenpox?"
People to focus on are non-pregnant women of childbearing age, international travelers, and people who live with or work around children. Adults and adolescents living in a household with children are recognized as a risk and a recommendation, but it's little bit lower on the list because you're talking about exposure to two or three children.
Then there's another important approach to consider. With varicella, you're not just protecting the patient from getting chickenpox - you're potentially stopping patients from spreading chickenpox to people who could get very sick, and that includes health care workers who come in contact with immunocompromised patients, pregnant patients, or others at risk. As a matter of rule, doctors and their office staff should all have received the vaccine if they aren't already immune to chickenpox.
And who shouldn't get the vaccine?
According to ACIP recommendations, people should not get chickenpox vaccine if they
- Have ever had a life-threatening allergic reaction to gelatin, the antibiotic neomycin, or a previous dose of chickenpox vaccine.
- Are moderately or severely ill at the time the shot is scheduled (they should usually wait until they recover before getting chickenpox vaccine.)
- Are pregnant. Women should not get pregnant for 1 month after getting varicella vaccine.
- And there are some people who should be reviewed on a case-by-case basis, such as anyone who has a compromised immune system, either from a disease or medication, anyone who has had a transfusion or were given blood products, and anyone who has cancer and is undergoing treatment.
Can doctors typically rely on taking a patient history for chickenpox?
Dr. Neuzil: If a patient says, "I know I've had chickenpox," 99% of the time that's correct and their blood test is positive for antibodies - so a positive history can be taken as a positive. But if a patient says, "I never had chickenpox," I would recommend confirming with serology, because 70-90% of those people usually show immunity. Many people were exposed sufficiently and have immunity to the disease, even without developing the classic lesions. This vaccine wouldn't hurt them if they did already have immunity, but would be an unnecessary expense and inconvenience.
Considering how many adults have either had chickenpox or been adequately exposed to it, how many patients need varicella vaccine?
Dr. Neuzil: It's a small percentage, but a significant one. While 98 to 99 percent of adults already have antibodies, the vaccination of the remaining one percent is important. Most doctors have seen a case of adult chickenpox and realize it carries far greater potential for complications than in children.
Why is pregnancy a concern when it comes to varicella?
Dr. Neuzil: If you develop varicella or chickenpox during pregnancy it's problematic for two reasons. One is that pregnant women tend to have severe disease with high rates of complication. The second is that their children can get congenital varicella syndrome or paranatal varicellla both of which are severe diseases.
Varicella is a live attenuated vaccine. Non-pregnant women who are vaccinated should avoid becoming pregnant for one month following each injection, which are four to eight weeks apart. Obviously if they got pregnant in between, you wouldn't give them two doses.
What would you say to a woman who became pregnant unexpectedly within a month of the vaccine?
Dr. Neuzil: The chances of a problem should be less than if they had developed chickenpox, but there really are too few women in that situation to give actual statistics.
Should people who are immunocompromised be concerned about being exposed to chickenpox after their child is vaccinated for it?
Dr. Neuzil: It is a live vaccine, but it's attenuated so any ability to transmit or cause a problem is much lower with the vaccine than with natural chickenpox. The only way you can catch virus-related chickenpox to somebody is if they get a rash. About one to three percent of people will get a varicella, a chickenpox-like rash after getting the vaccine. So if your child gets that rash after getting the vaccine, treat it as if it can be transmitted and avoid contact. But again, one to three percent is a fairly low incidence of that rash. *
How should doctors respond to people who argue, "If everyone is getting vaccinated, what's my risk for exposure?" as reason for not getting the vaccine?
Dr. Neuzil: There are two problems with that argument for varicella; one is that immunization rates among children, while increasing, remain relatively low as compared to other pediatric vaccines. The second problem is the recrudescence in the form of zoster. Unvaccinated adults can be exposed to varicella if they come in contact with adults who have zoster.
Does the varicella vaccine protect against zoster?
Dr. Neuzil: We don't know, but it is believed that children who receive the vaccine have lower incidences and less severe zoster than what follows natural infection.
There is a very large study in the United States of 38,000 people over the age of 60 to see if a high dose varicella vaccine can prevent zoster.* So it's a hypothesis being tested, but we won't have the results of that trial for three years.*
Will the infants receiving varicella vaccine eventually need a booster as adults?
Dr. Neuzil: That's another point we really don't know yet. The children in Japan who received the vaccine first are being followed to see how long immunity lasts, but it may well be that they will need a second booster dose in adolescence or adulthood. It's something that is being closely watched and will be reported upon.
Dr. Neuzil is the assistant professor of medicine, Division of Infectious Diseases, Department of Medicine at the University of Washington School of Medicine as well as a staff physician in the Division of Infectious Diseases, Department of Veterans Affairs Puget Sound Health Care System in Seattle, WA.
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