360: Measles IgG titers in a cohort of pregnant women in New York City

Abstract

As of 7/29/2019, there have been 642 confirmed cases of measles in NYC this year. Pregnant women and their fetuses represent a susceptible population to measles infection. Ideally, proof of vaccination against measles should be documented prenatally. In the absence of such data, measles immunoglobulin G (IgG) titers can be used. Prior studies conducted before the present measles outbreak showed maternal measles IgG titers (MIT) to be in the non-immune range between 3.1-16.5% of the time. The percentage of pregnant women with MIT in the immune range during the current measles outbreak is unknown. The measles immunity status of pregnant women admitted to Labor and Delivery (L&D) in our hospital between 5/1/2019 and 7/13/2019 was assessed by MIT drawn during pregnancy or upon admission to L&D. Results were described as immune, equivocal or non-immune. All pregnant women with titers deemed to be non-immune or equivocal were offered an MMR vaccine prior to discharge. In the study period, a total of 558 women delivered at our hospital and of those 523 (94%) had available MIT. 386 (74%) were in the immune range, 131 (25%) were in the non-immune range, and 6 (1%) had equivocal immunity. Only 89 (65%) non-immune mothers received the MMR vaccine prior to discharge. Of the 48 (35%) mothers who did not receive the vaccine, 54% was due to maternal refusal. The percentage of mothers with negative MIT in our sample was higher than expected. Negative titers to measles do not necessarily suggest non-immunity as some vaccinated individuals have negative titers but produce an immune response when exposed to measles. Given that proof of immunization may not be available, administering a booster dose of MMR vaccine to patients with a negative MIT is reasonable, especially during an outbreak.