Authors Call for Additional Research For Flu Vaccine. A study published in Vaccine suggests a strong tie between receiving repeated doses of the seasonal influenza vaccine and miscarriage, according to the Center for Infectious Disease research and Policy (CIDRAP News).
The authors said the study is an unexpected indication that calls for deeper investigation while also revealing the challenges of monitoring the safety of annual vaccines, notes CIDRAP News. “We are not saying this is a causal relationship,” said James Donahue, DVM, PhD, MPH, a senior epidemiologist at the Marshfield Clinic in Wisconsin and the lead author of the study. In other words, the data do not necessarily show that the flu vaccine causes miscarriages; however, “There’s no biological basis for this phenomenon, so the study represents something that wasn’t expected,” CIDRAP News reported.
The case-control study was conducted over two flu seasons—2010 to 2012. A total of 485 women experienced spontaneous abortion, or miscarriage and were matched with woman who delivered full-term live or stillbirths. Donahue and his fellow researchers were working to determine if spontaneous abortions were likelier to take place if a woman received the flu vaccine in the 28 days prior to the miscarriage.
The researchers did not find an association between miscarriage and flu vaccine if a woman had not received a vaccine during the prior year; however, in women who had consecutively received a flu vaccine containing the 2009 H1N1 virus, the researchers discovered an adjusted odds ratio of 7.7, while women who were not vaccinated in the previous season had an adjusted odds ratio of 1.3. The increased tie was seen in both of the seasons researched, according to CIDRAP News.
The researchers wrote that, “Science is an incremental process, and a lot of people don’t understand that very seldom does a single study provide a definitive answer that can lead to changes in recommendations,” said Edward Belongia, a senior epidemiologist at the Marshfield Clinic Research Institute in Wisconsin and one of the study authors, The Washington Post reported.
According to CIDRAP News, the overall adjusted odds ratio in the 28-day period was 2.0, or double the risk, but those findings, in contrast to the H1N1 subset, were not statistically significant. There was no association seen in any other exposure window.
“In a previous study conducted on flu vaccine and miscarriage, we did not see a risk,” said Donahue, referring to research conducted from 2005 to 2007. That study was conducted after the CDC made the recommendation in 2004 that all pregnant woman in every trimester receive get the seasonal flu shot. The CDC requested a follow-up study after the 2009 H1N1 pandemic,” CIDRAP reported. Donahue and his colleagues are working on a follow-up study that will focus on more recent flu seasons and will triple the number of cases.
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First of its Kind Research
The Washington Post noted that the study is the first of its kind to identify a possible association between miscarriage and the flu vaccine, as well as the first research to assess the effects of repeat influenza vaccinations and miscarriage risk. The research is preliminary; however, the research is likely to raise concerns regarding the vaccine and pregnancy as flu season gets underway.
Lone Simonsen, PhD, research professor of global health at George Washington University, said that she found the timing of the study interesting. Simonsen conducted her own research that revealed that, in 1918, when a prior H1N1 pandemic was circulating and was more severe than in 2009, as many as 1 in 10 women miscarried. “In this case getting the flu vaccine can be like being introduced to a virus that was evolutionarily quite similar to the virus from 1918,” she told CIDRAP News. Simonsen noted that the new study only included women who had a documented miscarriage. “Who are the women that document a miscarriage at five weeks?” asked Simonsen. “Probably someone who is also likely to get a flu shot.” If true, that would change the numbers, which would be closer to an association between the vaccine and miscarriage, noted CIDRAP News.
In an accompanying commentary in the same journal, three experts from the United States who were not involved in the research noted that miscarriage is among the most difficult birth outcomes to study in observational research. “Among other factors, the high proportion of [spontaneous] abortions [SAbs] that take place in clinically-unrecognized pregnancies and the lack of consistency in accurate capture of these events in medical records when SAbs do occur, make such research difficult to carry out,” they wrote. They noted that, “One important take-away message from this study is that seasonal vaccine formulations are not all the same…. As with other studies of drug safety in pregnancy, specific drugs require targeted post-marketing surveillance studies to monitor for safety, and the challenges are even greater for influenza vaccines, whose antigens and other components typically change each year.”
The researchers concluded, in part, that Sab “was associated with influenza vaccination in the preceding 28 days. The association was significant only among women vaccinated in the previous influenza season with pH1N1-containing vaccine…. but further research is warranted.
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