Vaccines are a marvel of medicine. Few interventions can claim to have saved as many lives. But it may surprise you to know that not all vaccines provide the same level of protection. Some vaccines stop you getting symptomatic disease, but others stop you getting infected too. The latter is known as “sterilizing immunity.” With sterilizing immunity, the virus can’t even gain a toehold in the body because the immune system stops the virus entering cells and replicating.