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COVID‑19 vaccine effectiveness

Medicine Cabinet

Thomas B. Cueni, director general of the International Federation of Pharmaceutical Manufacturers and Associations (IFPMA), emphasized that vaccine makers are fully committed to transparency in reporting clinical trial results. They likewise support the need to inform the public of what they know, as well as what they don’t know about the vaccines in development.

“We must prioritize thorough validation of the results of pre-clinical and clinical trials by independent expert bodies. Only the most rigorous application of science and openness in the regulatory process can ensure that everyone, starting with healthcare workers, has confidence in COVID-19 vaccines once they have been properly approved,” he wrote in an opinion piece (Financial Times, September 2020).

As the foremost representative of the global research-based medicines and vaccines industry, the IFPMA provides information on the effectiveness of coronavirus disease 2019 (COVID-19) vaccines.

It explained that Phase 3 clinical trials are the last and largest phase of vaccine testing before authorization or approval. These trials test how effective a vaccine is at preventing COVID-19 and are being conducted with tens of thousands of volunteers around the world. During Phase 3, some volunteers get a COVID-19 vaccine and some get a placebo, a harmless injection with no active drug or treatment, for example, like normal saline.

To learn how effective a vaccine is at preventing a specific disease, researchers assess the vaccine efficacy rate which compares (a) the number of volunteers who got COVID-19 after getting the vaccine being studied; and (b) the number of volunteers who got COVID-19 after getting a placebo. Thousands of people have volunteered to take part in different COVID-19 Phase 3 trials around the world. Some of these trials reported vaccine efficacy rates of over 90%.

All of the authorized COVID-19 vaccines go beyond the minimum efficacy level of 50% required by the Food and Drug Administration (FDA). This means that the FDA would not authorize a vaccine unless it prevented COVID-19 or lessened its severity in at least 5 out of 10 (50%) of people who got the vaccine. After a vaccine is authorized, health authorities continue to monitor its safety and effectiveness.

After receiving a vaccine, your body’s immune system needs a little time to learn how to detect and fight the virus. This maturation of the immune system can vary but is usually around a few weeks. Each authorized or approved COVID-19 vaccine has different speeds for how quickly it protects you. The speed of response can depend on factors such as the dosing schedules or the number of doses.

Based on clinical trial data of the currently authorized or approved COVID-19 vaccines, optimal protection is reached within a few weeks of vaccination. For two-dose vaccines, some early protection is achieved after the first dose.

It is too early to know how long COVID-19 vaccines will provide long-term protection. More research is needed to answer this question. The currently available data suggest that most people who recover from COVID-19 infection develop an immune response that provides at least some protection against reinfection (getting it again) — this is called natural immunity. We’re still learning how strong this natural immunity may be, and how long it lasts.

Health authorities will continue to monitor the clinical trial volunteers for many months to check how long they are protected. Both natural immunity and immunity from a vaccine are important aspects of COVID-19 that experts are trying to learn more about.

People ask if you can still get COVID-19 or spread the virus after getting vaccinated. The answer is maybe. Clinical trials have shown that COVID-19 vaccines significantly lower the chance a person will have symptoms, including hospitalizations and severe symptoms. However, none of the COVID-19 vaccines tested so far have been 100% effective at preventing COVID-19. So, some people who get the vaccine may still get the virus.

Furthermore, we still do not know if the vaccines will prevent someone who is infected (but doesn’t have symptoms) from spreading COVID-19 to others. Research tends to show that a vaccinated person is less likely to spread COVID-19 to those who are more vulnerable (have a higher risk of severe COVID-19 infection), similar to what happens with vaccines for other respiratory infectious diseases such as influenza.

This is why it remains important to continue washing hands, practice social distancing, and wear a mask even after you get a vaccine.


Teodoro B. Padilla is the executive director of the Pharmaceutical and Healthcare Association of the Philippines (PHAP). PHAP represents the biopharmaceutical medicines and vaccines industry in the country. Its members are at the forefront of research and development efforts for COVID-19 and other diseases that affect Filipinos.