Herd immunity

Virology

Virulence

Immune system

Influenza vaccine

Biochemistry

Infectious disease (medical specialty)

Attenuated vaccine

Disease

Coronavirus disease 2019 (COVID-19)

Biology

Pandemic

Gene

Vaccination

Live attenuated influenza vaccine

Immunity

Internal medicine

Immunology

Medicine

The Lancet Infectious Diseases

Live attenuated vaccines could have beneficial, non-specific effects of protecting against vaccine-unrelated infections, such as BCG protecting against respiratory infection. During the COVID-19 pandemic, testing of these effects against COVID-19 was of interest to the pandemic control programme. Non-specific effects occur due to the broad effects of specific live attenuated vaccines on the host immune system, relying on heterologous lymphocyte responses and induction of trained immunity. Knowledge of non-specific effects has been developed in randomised controlled trials and observational studies with children, but examining of whether the same principles apply to adults and older adults was of interest to researchers during the pandemic.

Beneficial non-specific effects of live vaccines against COVID-19 and other unrelated infections