What is a vaccine?
Provides protection against contracting a disease through antibodies.

How is the benefit of a vaccine measured?
“… according to the degree of protection it confers against a given pathogen. Two means of measuring protection exist: efficacy and effectiveness. While efficacy studies determine if a vaccine works under controlled conditions (degree of immunogenicity or ability to provoke an immune response in clinical trials), effectiveness studies are designed to determine if vaccination helps people (fewer diseased individuals in a long‐term follow‐up clinical trial or real‐life scenario) (Fedson 1998).

Can a Vaccine have Adverse Reactions?
A vaccine can have a range of adverse effects, from mild irritation to death. “Harms may be considered non‐serious (e.g. mild, transient headache) or serious (e.g. causing hospitalisation or death) and they may appear shortly after vaccine administration (e.g. pain at the injection site) or some time after (e.g. autoimmune responses). Vaccine toxicity, efficacy, and effectiveness may originate from, or depend on, a plethora of factors, including the vaccine components (e.g. the antigen itself, the excipient, or the adjuvant); interaction between different vaccine components; vaccine manufacture; overall vaccine composition; route of administration; dose; and number of booster vaccinations” Kocourkova 2017