Screening and vaccination

Screening and vaccination both aim to reduce future harm, but they work differently. Screening estimates who may need further assessment. Vaccination helps the immune system build protection. Neither provides certainty, and both require informed choice.

Two different preventive offers Screening and vaccination are often grouped together because both can reduce harm before serious illness develops. Their purposes and limitations are different. Screening identifies apparently healthy people who may have a higher chance of a particular condition. Vaccination gives a vaccine so the immune system can build protection against a specific infection or its effects. Both are usually organised as programmes with eligibility rules, invitations, information, follow up and quality checks. An invitation is an offer, not proof that something is wrong. It does not remove personal choice. Screening is a pathway, not one final test A screening programme usually starts with a test, measurement or questionnaire. It is offered to a defined group based on factors such as age, pregnancy, newborn status or recognised risk. A result showing a higher chance is often called a positive or abnormal screening result. It usually leads to more information, another test or diagnostic assessment. It does not confirm the condition by itself. A result showing a lower chance is reassuring, but it does not guarantee that the condition is absent. A false negative occurs when screening gives a lower chance result even though the condition is present. A false positive occurs when screening suggests a higher chance but follow up shows that the condition is not present. False positives can cause worry and may lead to tests or procedures that carry their own risks. Screening can also cause overdiagnosis. This means finding a condition or change that would never have caused harm during that person's lifetime. Overdiagnosis may lead to overtreatment, anxiety or long term medical labelling without benefit. A screening programme should therefore be judged as a complete pathway. The expected benefits must outweigh harms from testing, follow up, treatment and missed or uncertain results. Screening should support informed choice. People need balanced information about possible benefits, harms and outcomes so they can accept or decline the offer. Screening does not replace assessment of symptoms. New or persistent symptoms still need appropriate clinical advice, even after a recent reassuring screening result. Vaccination builds protection, not certainty Vaccination exposes the immune system to a controlled form of a target, or instructions for making part of it. The immune system can then respond faster if it later meets the infection. Immunisation is the process of developing protection after vaccination. The response varies between people, and no vaccine protects everyone completely. Vaccine effectiveness describes how well vaccination reduces outcomes such as infection, illness, severe disease or complications in real world use. The effect depends on the vaccine, infection, age, health and time since vaccination. Protection may take time to develop and may weaken. Some programmes therefore use several doses or later boosters. Vaccination is usually given before exposure. Some vaccines can also be used after a known or suspected exposure when prompt treatment can still prevent disease. The correct timing depends on the infection and programme guidance. Community protection varies For some infections spread between people, vaccination also reduces infection or onward transmission. High and evenly distributed coverage can then interrupt some chains of transmission. This indirect effect is called community protection or herd protection. It can help people who respond less well to vaccination, are too young for a particular vaccine or cannot receive certain vaccines. Community protection is not a perfect shield. Its strength depends on how the infection spreads, how well the vaccine reduces transmission, how long protection lasts and where immunity gaps remain. Not every vaccine creates meaningful community protection. Some mainly protect the vaccinated person because the target disease does not normally spread from person to person. Safety monitoring continues after approval Vaccines are tested before approval, but safety monitoring continues after they enter wider use. Large programmes can reveal uncommon effects that smaller trials may not detect. Most vaccine side effects are mild and short lived, such as soreness, tiredness or a mild fever. Serious side effects are much less common, and the known risks differ between vaccines. In the UK, suspected vaccine side effects can be reported through the Yellow Card scheme. The Medicines and Healthcare products Regulatory Agency, usually shortened to MHRA, reviews these reports. A report records a suspected event. It does not by itself prove that the vaccine caused it. The MHRA examines reports alongside clinical records, research and population data. They can update advice, restrict use or take other action when evidence changes the balance of benefits and risks. Trust also depends on fair delivery Programmes work only when eligible people can understand and access them. Language, disability, transport, appointment systems, mistrust and previous discrimination can all affect participation. Public health teams monitor uptake, outcomes and safety across different groups. The aim is not simply the highest possible uptake. It is an evidence based offer delivered fairly, with honest information and appropriate follow up.

Screening estimates who has a higher chance of a condition and may need follow up. Vaccination lowers the risk from specific infections. Neither gives certainty, and both require evidence, informed choice and monitoring.