A recent study linking flu shots and vaccines increasing the miscarriage risk leaves all pregnant women in a dilemma. This has raised a series of questions regarding the safety of flu vaccination though it is not being supported by the leading authorities.
The CDC, American College of Obstetricians and Gynecologists and the study authors are maintaining their stand strongly advocating flu vaccination during pregnancy. The research is still too weak and at the preliminary stage to change the preset advice. According to the opinion of a scientist involved in the research, a single study rarely provides a definitive answer and therefore changes in recommendations should not be based on that.
The research findings:
Scientists at Marshfield Clinic Research Institute in Wisconsin compared the miscarriage rates of two groups each comprising of 485 women whose ages ranged 18-44 years. One group had normal deliveries and the other suffered miscarriages during the flu seasons of 2010-11 and 2011-12.
In the group that miscarried, 17 women were found to have received flu shots 28 days before vaccination and also in the previous flu season. Most of the miscarriages happened in the first trimester and the median age of the fetus during miscarriage was 7 weeks.
When compared to the group having normal deliveries, 4 women who got a flu shot 28 days before delivery also received the same in the previous flu season. Somehow, the scientists feel that there is some association between receiving successive vaccination and risks of miscarriage.
The same research group conducted a similar study among pregnant women in the 2005-6 and 2006-7 flu seasons and found no such links between miscarriage and vaccination. The recent finding also has its share of limitations.
Firstly, it was carried within very small groups. Secondly, the women who miscarried may have already carried high chances of miscarriage not related to vaccination. Most miscarriages occur during the early stages of pregnancy and seldom catch the attention of caregivers.
Why are flu vaccines during pregnancy important?
In 1990s, CDC recommended flu vaccines for pregnant women in the second or third trimester of pregnancy to get vaccinated from influenza, a deadly disease with high risk of serious birth defects and miscarriage. This is also a protective step for the newborns because the vaccine cannot be administered to them before reaching 6 months of age.
The Advisory Committee on Immunization Practices (ACIP) in 2004 supported the recommendation from CDC advocating all pregnant women to go for this flu shot. A decade back, senior experts after a thorough data search collected from 2005-6 and 2007-8 flu seasons found no such link between flu-vaccination and enhanced miscarriage risks.
Could composition change be the trigger?
With the swine flu creating flu pandemic in 2009, the normally vaccinated virus got replaced. This is a normal action after any pandemic. Therefore, one of the seasonal flu viruses which used to be circulated in vaccines got replaced with a newer strain H1N1pdm09 bringing a change in the flu vaccine composition.
The rate of taking flu-shots leaped after the 2009 pandemics as more number of pregnant women took protective steps against influenza. The authors of the study are speculating if this increased miscarriage risk is an immunological response caused by taking two consecutive flu shots but that could not be scientifically established.
Flu vaccination – Is it a double edged sword?
Certainly, pregnant women now are at a crossroads. The reports of the ongoing study with pregnant women receiving flu shots during 2012-13 flu seasons are expected at the end of 2019. The director of Vaccine Research at the Mayo Clinic is strongly against the view that flu shots are in any way responsible for miscarriages.
Considering flu as a bigger threat than the shot, the head of the committee on maternal immunization has expressed deep concerns that an undesirable panic may prevent pregnant women taking flu shots and invite a bigger crisis.