How vaccines are approved and monitored

Vaccines are among the most strictly regulated medical products in the world. Unlike ordinary medicines, which are generally taken to treat an existing illness, vaccines are typically administered to healthy populations to prevent disease. This fundamental difference drives a highly demanding approval and monitoring framework. Because the tolerance for adverse effects is much lower when treating healthy people—especially infants—the regulatory hurdles for vaccines are exceptionally high. From the initial laboratory development to post-market surveillance, vaccines are subjected to layers of oversight that go beyond the standard requirements for conventional drugs.

How vaccines differ from ordinary medicines

Most conventional medicines are small-molecule chemical compounds. They are manufactured through predictable chemical reactions, and the final product is a defined molecule that is relatively easy to replicate. Vaccines, by contrast, are biological products. They are often derived from living organisms, such as weakened bacteria or viruses, and may be produced using complex biological systems like chicken eggs or mammalian cell cultures.

This biological nature means that the final product can vary slightly based on how the living organisms behave during production. Because of this inherent variability, the manufacturing process itself is heavily scrutinised. Regulators do not just test the final product; they evaluate the entire facility, the production process, and the consistency of every step. Furthermore, the clinical trials for vaccines often require tens of thousands of participants to ensure that they are safe and effective across broad demographics. Regulators evaluate whether the immune response generated by the vaccine is sufficient to provide protection, a standard that differs from simply measuring symptom relief in ordinary drug trials.

WHO prequalification for vaccines

While national regulators approve medicines for their specific markets, many countries rely on the World Health Organization (WHO) for additional assurance, particularly for vaccines procured through UN agencies. The WHO prequalification process evaluates the quality, safety, and efficacy of vaccines produced by manufacturers globally. This is vital for ensuring that low- and middle-income countries can access safe immunisations without having to duplicate the extensive laboratory and clinical assessments performed by stringent regulatory authorities.

To achieve prequalification, a manufacturer must demonstrate that their vaccine meets international standards and that their production facilities operate to strict quality guidelines. The WHO also performs site inspections and tests independent samples. In South Africa, the South African Health Products Regulatory Authority (SAHPRA) regulates medicines locally, but vaccines procured for the national immunisation programme commonly carry WHO prequalification. This dual layer of oversight ensures that the products meet globally recognised standards before they are distributed.

Batch release testing

A major distinction between vaccines and ordinary medicines is the requirement for batch release testing. For most standard drugs, once a manufacturing process is approved, regulators generally test occasional batches to ensure ongoing quality. For vaccines, every single batch—often referred to as a lot—must be individually tested and released before it can be distributed.

Because biological products are sensitive to minor changes in temperature or manufacturing conditions, a problem in one batch does not necessarily mean the next batch will have the same issue. Batch release testing is typically performed by both the manufacturer and an independent National Control Laboratory. This testing verifies the vaccine's identity, purity, sterility, and potency. If a batch fails even one of these stringent tests, it is destroyed. This independent verification acts as a final safety net, ensuring that the specific vials given to the public meet the exact standards approved by regulators.

Ongoing monitoring after approval

Once a vaccine is approved and enters the market, monitoring does not stop. Pharmacovigilance—the process of monitoring the safety of medicines after they are approved—is particularly rigorous for vaccines. Because vaccines are administered widely and often simultaneously, rare adverse events that might not have been detected in clinical trials can emerge only when millions of people receive the product.

Many countries maintain dedicated vaccine safety monitoring systems, sometimes separate from their general pharmacovigilance programmes, to rapidly detect and investigate potential side effects. These systems often use active surveillance, where registries cross-reference vaccination records with health outcomes to detect patterns automatically. Regulators continually review data from healthcare providers and the public to ensure the benefits of a vaccine continue to outweigh any risks. Patients and healthcare professionals can use tools like HealthSA to verify the registration status of vaccines and other medicines in South Africa, but reporting any adverse events directly to SAHPRA remains a crucial part of this ongoing safety net.