Why is there a waiting period between the two shots? Is the window to get the second shot flexible?
The waiting period between the two vaccines is a well-thought-out scientific process based on historical research and the time it takes for the immune system to respond after receiving the first dose.
The first dose of the mRNA COVID-19 vaccine is called the ‘primer dose,’ which wakes up the body’s immune system and recruits the appropriate immune cells (antibodies, T cells, macrophages, etc.). These are the soldiers that respond to an invader or enemy in your body. Just like the training process of soldiers, which takes time, the process in humans and non-human primates takes about 2-3 weeks.
The second dose of the vaccine called the ‘booster dose,’ is then given at 3 weeks for the Pfizer vaccine and 4 weeks for the Moderna vaccine. This will boost the levels of immune cells for optimal protection against future exposure to SARS-CoV-2, the virus that causes COVID-19. After another two weeks of the booster dose, the ‘immune soldiers’ will be well trained to win the battle against the virus.
The second dose should preferably be given as stated above (3 weeks for Pfizer and 4 weeks for Moderna), but if it is not possible to adhere to the recommended interval, giving the second dose 4 days earlier or up to 6 weeks (42 days) after the first dose is still acceptable according to the CDC.
Henry Anyimadu, MD
Infectious Disease Specialist