Days after pharma major Pfizer announced a possible breakthrough in the development of a vaccine for Covid-19, Dr Randeep Guleria, Director, AIIMS Delhi commented on the news. While calling it a positive development in the race to end the ongoing pandemic, Dr Guleria pointed out various challenges linked to the vaccine. He said that Pfizer's data hadn't been reviewed by experts yet and there was a need to look at various aspects of the study. Dr Guleria said that it needs to be seen how long the immunity produced by the vaccine lasts, and also whether it protects against mild, moderate or severe Covid infection. The other challenge linked to Pfizer's vaccine is its storage. The inoculant needs to be stored at minus 70 degrees Centigrade, making it difficult to take it to small towns and rural areas. Phase 3 human trials of the vaccine developed by Pfizer and BioNTech are still underway. Watch the full video for more.