In a recent podcast posted on NPR, the practice of mixing different kinds of COVID-19 vaccines was discussed. Typically, if you get a COVID-19 vaccine that requires two doses, you should get two of the same vaccine. Two Pfizer shots, or two Moderna shots, not one and then the other.

“In the U.K. at the moment, we’re sort of calling it ‘mix and match’,” says Helen Fletcher, a professor of immunology at the London School of Hygiene & Tropical Medicine. She says shortages of a vaccine or concerns about side effects may induce health officials to adopt a mix-and-match strategy. Basically, all vaccines work by showing people’s immune systems something that looks like an invading virus but really isn’t. If the real virus ever comes along, their immune systems will recognize it and be prepared to fight it off.

Using two different vaccines is like giving the immune system two pictures of the virus, and if you give two different types of vaccine, then you tend to get a better immune response, “if you give the same vaccine twice”, said Fletcher. Stay well and stay tuned!