Monday, May 11, 2009

Vaccine Dinner Club: Simultaneous Administration of Vaccines

Wednesday night, I attended a meeting of the Vaccine Dinner Club at the Emory University School of Medicine. This group of clinicians, researchers, policy makers, and other interested parties meets monthly in Atlanta to discuss issues related to vaccines. This is sort of tangential to my own research, but the May meeting theme (Simultaneous Administration of Vaccines: How Many is Too Many?) is a hot topic right now, so I was interested in hearing what the speakers had to say. Plus, they serve food and drinks. If you're in Atlanta and think this sounds like a good deal, I encourage you to click the link and learn more about the club -- it's free to join and to attend the nosh-filled meetings.

I must admit that I am a bit hesitant to make this post, because so many people have such strong opinions about immunizations these days, but I think it's important to share the kinds of things that experts talk about when they get together. This contributes to public education on the subject of vaccines, and it also lets people know that their concerns are being heard, and that medical professionals are trying to understand and alleviate them.

This month we heard from Andrew Kroger, MD, MPH, and Melinda Wharton, MD, MPH, both from the Center for Disease Control's National Center for Immunization and Respiratory Diseases. I did my best to takes notes during both talks, and I'll try to hit the key points in this post, but you should know that I'm not a doctor or a vaccine expert, so my interpretation of these lectures may be inaccurate. If I write something in error, please blame me and not Dr. Kroger or Dr. Wharton.

Dr. Kroger, a medical health educator, gave the first talk. He discussed the current vaccination recommendations established by the CDC, which cover a total of 17 different vaccines administered to children, adolescents, and adults. Because we now have the ability to protect against more diseases with vaccinations, people are getting more shots. Simultaneous administration of vaccines (which is defined as getting two or more shots during the same doctor's visit; not to be confused with combination vaccines, which consist of multiple antigens in a single syringe) is a strategy used by health care providers to ensure that people receive all of the recommended immunizations within the appropriate time frame. Dr. Kroger cited several studies indicating that giving two vaccines in one office visit is just as effective as giving them separately. In fact, it can sometimes be more effective. If vaccines are not administered simultaneously, they should be spaced out by at least one month. Giving two vaccines within the same month can lead to reduced efficacy of the second vaccine. Giving both shots at once, however, induces an immune response that is just as effective as the response to individual vaccines that have been spaced further apart. The only vaccines for which simultaneous administration is not recommended are varicella and smallpox. This is because doctors need to be able differentiate between the two diseases in the event of an adverse reaction. That is, if the shot gives you the pox (this is extremely uncommon, but possible), doctors want to be sure they know which pox you have, so they can treat it properly.

The CDC has been recommending simultaneous administration of vaccines for many years, but has added eight new vaccines to the recommended schedule since 1994. Dr. Kroger investigated simultaneous administration of these newer vaccines to see whether the historical data held true for them as well. You can find a wealth of information on this subject at the FDA's vaccine website. Dr. Kroger spent quite a while summarizing studies on new vaccines, and concluded that while we haven't rigorously tested every possible combination of shots (there are a lot of them), none of the studies conducted thus far present a contraindication for simultaneous administration.

Dr. Kroger went on to a bit of basic immunology, explaining why it's possible for our immune system to handle simultaneous vaccines. It comes down to a bit of math. Seroprotection (the goal of vaccination) is defined by antibody levels of 10 ng/mL of blood. To achieve this within a week of vaccination, only one B cell clone is needed per immune epitope for each mL of blood in the body. A typical vaccine contains about 100 epitopes for each disease that it protects against, so we need 100 B cells/mL of blood to achieve seroprotection for a disease within one week of vaccination. One mL of blood normally contains about 10 million B cells, so a healthy immune system should easily be able to handle several vaccines at once while still responding to other antigens that the body encounters.

These data left me convinced that simultaneous vaccines are effective. But are they safe? Fewer studies have been done on safety than efficacy, and there are data that indicate certain vaccine combinations can lead to a higher risk of side effects than individual administrations. Dr. Wharton, the second speaker, discussed these issues during her talk. While Googling for some of the studies she mentioned, I found this PowerPoint presentation, which is similar to the one she gave at the Vaccine Dinner Club. I suggest downloading it and looking through the slides if you're interested in this subject, as she covers more material relevant to common concerns about vaccine safety than I could possibly summarize here. The take-home message seems to be that while simultaneous vaccines may increase the incidence of side effects, these side effects are already rare, such that any additional risk caused by simultaneous administration doesn't make a huge difference. (Studies cited in Dr. Wharton's talk involved the combination of MMR and varicella vaccines. One study tracked over 531,000 children, divided into cohorts who received single, simultaneous, or combination vaccines. Only about 1% of the children across all groups were brought back to their doctor for fever symptoms after vaccination. The incidence of more severe complications, like febrile seizures, was much lower -- about 0.1%, with similar rates for sequential and simultaneous vaccines.) Parents who wish to take every possible precaution can ask their pediatrician about spacing vaccines out over several months, but this can present practical concerns for people who must take time off from work, arrange care for other children, and pay office fees during each trip to the doctor. If these issues create enough of a stumbling block, children might not be brought back for subsequent vaccines in a timely manner. And it's crucial to have children vaccinated within the recommended age range to protect them as early as possible from potentially fatal diseases. Delaying vaccination over concerns about simultaneous administration also delays protection against those diseases, so the relative risks must be balanced. While it is important to acknowledge that some children suffer unpredictable complications from vaccines, the optimal way to understand and prevent those complications is to come up with better screens for risk factors, not to simply stop vaccinating.

I thought Dr. Wharton brought up some excellent points during her discussion of risk communication with patients and parents on the subject of vaccines. Concerned parents will often reject expert opinions in favor of advice from individuals that they feel to be more caring and compassionate, even if that advice is misguided or inaccurate. It's important for healthcare providers to communicate effectively with parents, letting them know that not only do scientific studies support the importance, efficacy, and safety of vaccines for all children, but that adhering to a vaccination schedule is the best way for them to protect their child. Doctors with children of their own should be candid about their decision to vaccinate, and all physicians should make it clear that providing preventative medical care is the role of every loving mother or father. One survey of parents found that the most common concern with simultaneous vaccination comes not from spurious connections drawn between vaccines and conditions like autism, but from the additional pain and stress that children experience when receiving multiple shots. A kinder bedside manner can help with this problem, although it may be impossible to keep a child completely calm when he sees a needle coming.

The internet is teeming with discussions of vaccine safety and the dangers of the anti-vaccination movement, of course. For further reading on the subject, you can check out this article in the New England Journal of Medicine on vaccine refusal, Chris Mooney's summary of the vaccine/autism controversy in the June issue of Discover Magazine, and med student blogger Whitecoat Tales' Hard Conversations: Vaccines and Autism series.


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