Kindly chicks get easily chilled, check on your brooding temperatures. Post vaccination reactions normally observed within the first 3 days. If your area is currently cold with the current rains take care of the chicks properly. However remember that vaccinations doesn't eliminate other pathogens from your flock. Further more remember the period following vaccination, the immune system of the birds is always over work as it tries to develop resistance to the introduced vaccines hence the warning ⚠ that never vaccinate any birds that already show signs of illness otherwise their immune system will be overwhelmed in try to fight the disease as well as respond to the vaccine.