Kindly not that vaccination is meant to boost immunity. Vaccines only work well when done timely on healthy animals. Vaccinating your flock and exposing the to disease causing microoganisms is similar to vaccinating a children and keeping them in dirty environment under the pretex that they are vaccinated. Kindly observation of hygiene is the surest way of keeping diseases at bay. Kindly check your chicken house well and the rule of thumb is if you can't stay in it for more than 30mins then it is not best for your poultry too.