Zika and Pregnancy-Specific Vaccines: Toward Easing the Difficulty
The CDC announced today that the number of pregnant women in the U.S. infected with the Zika virus has tripled from 48 to 157. The escalation is a reminder of how difficult a public health emergency Zika will be to address given the complex nature of its victims. In my last post, I explained how a Zika vaccine (and vaccines in general) face numerous regulatory obstacles when developed for diseases for which inoculation during pregnancy is the most promising intervention. In this post, I explain why addressing those obstacles is such a significant public health issue.
Improving the current system for development and licensure of maternal immunizations is critical not only for public health emergencies like Zika but for the next generation of preventative health measures that are likely to make major gains in global public health. The history of increased global access to childhood immunizations has been one of the great public health stories over the last several decades. Between 1980 and 2012, cases of diphtheria and measles have declined by 95%; pertussis by 90%; tetanus by 91% and polio by 99% or more. These numbers show that beneficiaries of commitments to expand vaccine access are not limited to those receiving immunizations. In this time period, the population has increased 60%. Beyond those extraordinary outcomes are long-term benefits: vaccinated children remain healthy which contributes to better cognitive development and therefore better use of educational resources, lower societal healthcare costs, smaller families with healthier mothers and ultimately healthy workforce populations.
Although additional childhood and adolescent vaccines are being developed, immunizations for pregnant women represent a next step, supported by a great deal of preliminary evidence, in the effort to ensure that mothers remain healthy during pregnancy and children are born with as great a chance as possible to lead healthy lives. Vaccination of women during pregnancy is considered to be the most plausible strategy to provide direct antibody protection against respiratory syncytial virus (RSV) to young infants during the period of greatest vulnerability. The main limitations on the production of a Group B streptococcus vaccine are not technical or scientific, but regulatory and legal. Many other promising maternal vaccines remain stalled at the conceptual stage.
There are movements toward greater safety evaluation in this area and clinical trials are now underway for some recommended maternal vaccines like influenza and pertussis. But overall there is a lack of standardization for definitions of outcomes as well as ways to measure outcomes. This lack of standardization prevents the generalizability of safety data and extrapolating conclusions from more than one data set. Moreover, the ability to assess risk versus benefit relies on background rates of certain risks relevant to pregnancy like first trimester miscarriage. Without robust data as to these baselines, clinical trials involving pregnant women will not be able to adequately convey risk and benefit. With concerted effort and a willingness to have a conversation about the benefits of maternal immunization, at least some of the tremendous gains realized in the context of childhood immunization might be extended.