Delaying Covid vaccine second dose can reduce case numbers in near term, says study March 10, 2021 Robust immunity needed for longer term Researchers at Princeton University and McGill University conducted a study that suggests that delaying the second dose of Covid-19 vaccines should reduce the case numbers in the near term. However, the longer-term case burden and potential of evolution depend on the robustness of the immune response. Lead author Chadi Saad-Roy, a PhD candidate in Princeton’s Lewis-Sigler Institute for Integrative Genomics, said: “Several countries including the UK and Canada have stated that they will delay the second doses of Covid-19 vaccines in response to supply shortages, but also in an attempt to rapidly increase the number of people immunised.