Pfizer and BioNTech say their 1st pregnant participants have been given shots.
Ths is a large-scale clinical trial to assess the safety of their covid vaccine for pregnant women. 
The companies want to enroll 4,000 pregnant women in the trial.
They estimate the trial will finish by January 2023. 
Moderna, maker of the only other vaccine being given in Lexington, opened a registry to track pregnant women receiving the shot.
Pfizer and BioNTech also plan to:
• Study younger children and has started trials in adolescents. 
•  Evaluate the vaccine in those with compromised immune systems.
The National Institutes of Health believes pregnant women face greater risk of severe illness from the virus.
Pregnant women were excluded from the original Moderna and Pfizer trials.
'Pfizer and BioNTech say their research found no evidence of fertility or reproductivity toxicity in animals.
Some participants in Moderna's and Pfizer's US trials became pregnant and no vaccine problems were reported.