Fewer than four in ten pregnant women in America follow the public health recommendation to get a flu vaccine. Although this percentage is a lot lower than public health officials might like to see, it is still remarkably high when you consider the dangers.

Worries by mothers-to-be about potential harm to their fetuses are the main reason many choose to avoid the jab, and their concerns are justified. Unfortunately, a lot of pregnant women aren't hearing about studies like one from a team of South African researchers that compared four outcomes for infants whose mothers were given flu shots during pregnancy versus those who were given a placebo. They found that the shot was ineffective at lowering the risk of the outcomes studied, which were low birth weight, preterm birth, small for gestational age birth and fetal death.

Perhaps even more concerningly, they found that the infants whose mothers were vaccinated actually fared worse on these metrics.

The study was a large randomized, placebo-controlled, double-blind study involving more than 2,000 mothers who were given the flu shot or a placebo during the second or third trimester of pregnancy. The researchers then followed up on fetal outcomes once the infants involved reached 24 weeks of age.

Another interesting finding was that the average gestational age at birth in the vaccinated group was lower than that of the placebo group, which is a statistically significant result pointing to a greater risk of preterm birth from the shot.