A study published in the journal Vaccine has identified an association between the flu vaccine and miscarriage. The finding of the study is quite narrow: women who had a spontaneous abortion (SAB) were more likely to have received flu vaccinations during the 2010-2011 and 2011-2012 flu seasons. The study's authors are cautious about their conclusions: "This study does not and cannot establish a causal relationship between repeated influenza vaccination and SAB, but further research is warranted."
That disclaimer isn't stopping needless panic in pregnant women as this is a finding tailor-made for clickbait. This article is spreading like, well, the flu, and is likely to significantly impact pregnant women's behavior at doctors' offices this flu season.
Some analysts have already offered good reasons not to panic. Emily Ramirez at Pregnant Chicken suggests that the 2010-2012 flu vaccine, which was developed in response to H1N1, was a unique vaccine, so findings based on miscarriages during that period might not be applicable to other years. Lena H. Sun at the Washington Post notes that the median age of miscarriage recorded in the study was seven weeks, a time when the risk of miscarriage is high and when many women don't even know they are pregnant. Sun hypothesizes that the flu vaccine-miscarriage link could be explained by some women's overall use of health care. The women in the study who had miscarriages were enrolled after seeking medical treatment for their miscarriages. Women who seek treatment for miscarriage are also more likely to pursue other preventive health measures (like flu shots), which might explain the association discovered by the researchers.
One more reason not to panic has nothing to do with the specific study findings, or with the particular time period that was studied. It's where the article was published.
When a scientific finding gets reported in the news, the title of the journal is often an afterthought. In sparse Associated Press Style, the journal isn't italicized or underlined, so it often doesn't even stick out to readers. But the journal titles often offer helpful clues to readers trying to interpret a study's findings.
One of those hints is a journal's "impact factor," a number that shows its importance relative to other journals in its field. A journal's impact factor is calculated by totaling all the citations of articles from the previous two years and dividing it by the total number of articles published in the journal during that time. The result is the average number of citations each article in the journal receives.
Impact factors are not without controversy. Averaging the citations for a journal's article makes it appear as though all articles are equally influential, when of course there is often great variety of impact. Furthermore, practices like publishing literature reviews (summaries of the known scientific literature about a topic), tend to up a publication's impact factor because they are widely cited.
Although it is an imperfect measurement, a journal's impact factor offers a sense for the journal's prestige. The higher the impact factor, the more prestigious the journal. The 2016 impact factor of the Journal of the American Medical Association is 44. For The New England Journal of Medicine, it's 72.
The 2016 impact factor of Vaccine is three.
Does this mean the articles in Vaccine are not credible? Not at all. It just means that they are not frequently cited by other medical researchers.
There could be many reasons for lower citation rates. A low impact factor could be an indicator that the journal's articles are not considered credible by other researchers. But a low impact factor could also indicate that the topics studied by the journal are for a narrow audience of specialists.
Although an impact factor can't tell you whether an article in a journal is good or even true, it does tell you that it is expected to be a field-transforming article. Both the New England Journal of Medicine and the Journal of the American Medical Association frequently run articles about vaccines. You can bet that if the authors of this article had identified a causal link between the flu vaccine and miscarriage, they would have published in one of those journals.
The New York Times interviewed Vaccine's editor-in-chief Gregory Poland about his decision to publish these findings. Poland asserted that the piece was well-designed and raised an important question. But when asked if he thought the flu vaccines caused the miscarriages, he answered "Not at all." The Times piece also mentions that this article was rejected at two other publications before being accepted at Vaccine, but that fact should not be taken as a marker of quality. Scientific researchers regularly submit multiple times before receiving an acceptance.
The authors of the study assert that the findings should not change vaccine policy. The editor of the journal that published the study thinks that the flu vaccines were not the cause of the miscarriages. And yet, the reporting of this article is leaving readers with exactly that interpretation.
This brings us to an important question. Who are the results of scientific research for? Should the public be reading the tentative conclusions of scientific journal articles? Should journalists be reporting on them?
This study does not suggest any behavioral change for pregnant women. Instead, it poses an interesting question for future research: is there something different about that 2011-2012 vaccine that is not yet understood? Could further study of that vaccine contribute to increased vaccine safety?
These are great questions for "the pre-eminent journal for those interested in vaccines and vaccination." These are terrible questions for pregnant women, or soon-to-be-pregnant women, or women who experienced miscarriages who are now blaming themselves for getting vaccinated.
Perhaps that's why, ahead of Vaccine's publication of this article, the Centers for Disease Control and Prevention issued a preemptive "warning" to the American Congress of Obstetricians and Gynecologists, not about any dangers posed by flu vaccines, but to "help them prepare for a potential wave of worry from expectant moms."
It would be unfair to expect scientific journals not to release their results to the public; in fact, doing so would slow the pace of scientific discovery. It would likewise be unfair to expect journalists not to report on those findings. But it's even more unfair to drop such findings in front of readers – readers who will make health choices based on those findings – without providing appropriate context for interpretation.