The timing
couldn’t be better - or worse - for flu
shots this year. Pharmacies, medical
offices, clinics and employers are all offering influenza vaccine now to help
protect people from the flu whenever it strikes in a few months. As an Infectious Diseases Specialist, I
believe that flu shots are important and can save lives, but what I heard on
the news this morning worries me - a report potentially linking an increase in
early miscarriages among certain women who received influenza vaccination. The finding is so preliminary and information
so limited that it’s hard to draw any conclusions.
So why am I worried? I’m concerned that many pregnant women who
may have already been skeptical about receiving a vaccine will refuse a flu
shot, placing them and their unborn children at increased risk for severe
disease – even death. And the
anti-vaccine movement may seize upon this report, creating panic and blowing it
out of proportion to all of the evidence supporting the benefits of influenza
vaccination, particularly in the most vulnerable populations (young children,
the elderly, those with chronic illness, immune disorders, and pregnant and
postpartum women) who are at higher risk for severe illness and complications
from influenza.
The case-control
study in question funded by the CDC and conducted from 2010 to 2012 matched 485
women who experienced miscarriages with 485 who delivered full-term. Those who
had been vaccinated against influenza 28 days before the miscarriage, and in
the first trimester of pregnancy, were more likely to have had a miscarriage if
they had also been vaccinated the previous flu season with a vaccine containing
the 2009 H1N1 virus (adjusted odds ratio of 7.7), suggesting that repeat
vaccination may have led to a potential increase in the a proinflammatory
response associated with the H1N1-containing vaccines. There was no association
between miscarriage and flu vaccine if a woman had not received a vaccine in
the previous year (aOR of 1.3) and no association seen in any other exposure
window.
The CDC is
looking into this potential signal to determine if there is evidence for true “cause
and effect” rather than just an association, so the finding is far from definitive.
For example, it would be important to know whether these women had certain underlying
medical conditions prompting them to seek annual vaccination that could have
also placed them at increased risk for miscarriage. Only women who had clinically confirmed miscarriages
were studied, so the proportion of women with clinically unrecognized pregnancy
loss was uncertain. Results could have been biased if women who recognized and sought
care for miscarriage were more likely to have been vaccinated in the 28-day
exposure window.
Even though routine
annual influenza vaccination is recommended for all persons aged ≥6 months who
do not have contraindications, many people avoid getting vaccinated. The CDC recommends that all women who are
pregnant or who might be pregnant in the influenza season receive influenza
vaccine. This often occurs during the second and third trimesters, and prior published
studies have shown that vaccination during pregnancy is not only safe, but
beneficial to both the mother and the baby.
Despite this morning’s
news and preliminary report, I hope physicians caring for pregnant women will “keep
calm and vaccinate”!
Judith Wolf, MD
Associate
Director, WHEP
Donahue et al. Association of spontaneous abortion
with receipt of inactivated influenza vaccine containing H1N1pdm09 in 2010–11
and 2011–12. Vaccine. 2017; 35: 5314–5322 http://dx.doi.org/10.1016/j.vaccine.2017.06.069
