An immunization update

Studies of earlier influenza pandemics and large epidemiologic studies of otherwise healthy pregnant women who contracted nonpandemic seasonal influenza have similarly demonstrated how pregnant women and their infants disproportionately experience severe sequelae.

We need to inform our pregnant patients that the influenza vaccine protects their newborns as well as themselves. We must also work harder to dispel misconceptions about the safety of the vaccine.

One barrier to pregnant women receiving the 2009 H1N1 influenza vaccine was perceived risks to the fetus (Am. J. Obstet. Gynecol. 2011;204:S124-7). The source of much of this concern stems from the fact that some influenza vaccines contain trace amounts of the preservative thimerosal.

Influenza vaccines that contain a mercury-free preservative are available, but pregnant women should be informed that the Centers for Disease Control and Prevention (CDC), the Institute of Medicine, and numerous other health organizations have concluded that the thimerosal used in the vaccine is safe. The only flu vaccine that pregnant women should not receive is the attenuated vaccine.

An additional concern for some is that the influenza vaccine contains chicken egg protein, an allergen for some individuals. However, the CDC’s Advisory Committee on Immunization Practices now recommends that individuals who have only had hives after exposure to egg should receive the influenza vaccine, though physicians should take extra precautions, such as observing these patients for at least 30 minutes after administering the vaccine (www.cdc.gov/flu/professionals/acip/2013-summary-recommendations.htm).

With influenza immunization, we should celebrate our successes. As described in ACOG’s Committee Opinion on integrating vaccinations, vaccination of pregnant women increased nationwide to a level of approximately 50% in 2009, a significant increase over pre-pandemic rates of approximately 15%. Rates during the 2011-2012 influenza season remained approximately 47%.

Such improvement shows that immunization is achievable in our practices. However, rates hovering around half of all pregnant women are still just slightly north of mediocre. We should continue to make the benefits of vaccination clear to staff and patients, and the algorithm for implementation simple.

Given that the flu season begins in October and can run into spring – and that it takes about 2 weeks for production of protective antibody levels – it is rare that a pregnant woman will not need the vaccine.

Full recommendations for the prevention and control of influenza in 2013-2014 were expected at the time of this writing to be published in the Morbidity and Mortality Weekly Report.

Tdap

Pertussis is highly infectious, and infants who contract the bacterium have increased rates of whooping cough attacks and are at the greatest risk for severe disease and death. Pertussis outbreaks have become common in the United States, and can be difficult to identify and manage. Infants continue to have the highest reported rates.

When immunization is an integral part of one’s office (with standing orders, etc.), administering a dose of Tdap during each pregnancy to prevent pertussis in infants – as is recommended in the CDC immunization schedule released in January 2013 – should be relatively simple during prenatal office visits.

The postpartum "cocooning" approach recommended by the CDC in 2006 and supported by ACOG has been practically and logistically difficult to implement. While the concept is sound, it has proved too cumbersome overall to vaccinate every family member and caregiver who will have close contact with an infant. Merely having the parents vaccinated immediately postpartum – the other part of cocooning – has been difficult enough.

The new recommendations draw upon the proven paradigm of maternal vaccination for newborn benefit and the relative ease of immunization during prenatal care visits. Ob.gyns. should administer a dose of Tdap during each pregnancy – optimally between 27 and 36 weeks’ gestation – irrespective of the patient’s prior history of receiving Tdap.

Infants do not start their vaccination series against these pathogens until age 2 months; maternal immunization in late pregnancy leads to high transplacental antibody transfer, which will protect infants until they receive their own vaccines.

Although the optimal timing for maternal Tdap immunization is later in pregnancy, the vaccine may be given at any time if necessitated by clinical circumstance. For example, if a woman steps on a rusty nail during her first trimester and has not had a tetanus booster in the prior 5 years, or if a local school reports an epidemic, she should receive the Tdap vaccine immediately.

Cocooning is now the default; if Tdap is not administered during pregnancy for some reason, it should be administered immediately postpartum, with as much cocooning as possible.

The challenge with the Tdap vaccine is that few people who live outside areas where pertussis epidemics have occurred know someone who has had the bacterial disease. Education and a direct recommendation for the vaccine are therefore critical.