Response actors need to be able to explain vaccines and related terms in clear, concise, and actionable language through trusted sources. This communication may be easier with the aid of videos or illustrative articles. The video below from the Vaccine Knowledge Project is useful because it visualises the immune system and how vaccines harness the natural activity of our immune system in a way that’s easy to understand and explains key technical terms. WHO’s “Vaccine Explained” and “Science in 5” series also provides a structured set of illustrated articles on how vaccines work, how they are developed and the different types of vaccines available. Furthermore, the Johns Hopkins COVID-19 Training Initiative has developed three training modules on vaccines for health care workers, including how to communicate about them (“Building trust in vaccination through communication”).

What are vaccines and why should we promote them?

Vaccines are preventative - they are used to prevent infection, serious illness, and death. Vaccines are designed to teach the body’s immune system to recognise, and therefore be able to stop, the cause of a specific disease before it can make someone ill.

How do vaccines work?

The immune system is the part of the body that fights infection and disease. The active ingredient in different types of vaccines is made from deactivated or non-infectious organisms or a part of the organism (e.g. a protein) that you are trying to train your body’s immune system to stop. The part of the organism is called an antigen and can’t cause disease. When your immune system is introduced to these harmless antigens in very small amounts through vaccination, it learns what the cause of an illness (e.g. a specific virus or bacteria) ‘looks like’ so that your immune system builds specially targeted antibodies ready to fight off any future infection with this type of organism. This means that if you are fully vaccinated and get infected with the actual organism months, or for some vaccines years later, your immune system will recognise it and destroy the invading organisms before it causes disease.

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How have vaccines been used to combat public health problems throughout history?

Millions of people are alive today due to vaccination. Vaccines have helped reduce the global burden of tetanus, diphtheria, and measles and can now combat epidemics such as Ebola and cholera. The first vaccines were introduced in the 18th Century. Today, most countries have routine vaccinations, often known as ‘routine immunisation’ programmes, which are given to people at different stages of their life, usually starting in childhood. Research estimates that routine vaccination against 10 common diseases (such as Hep B, rotavirus, measles, and rubella) has prevented 37 million deaths between 2000 and 2019.

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How were the COVID-19 vaccines made?

The COVID-19 vaccines have been developed and approved through a rapid, yet safe, process due to emergency funding and unprecedented levels of global coordination and collaboration. This has been possible for a number of reasons. In part it is because COVID-19 is not the first coronavirus to threaten health in recent years. From the Severe Acute Respiratory Syndrome (SARS) coronavirus in 2003 and Middle East Respiratory Syndrome (MERS-CoV) coronavirus in 2012, scientists have had a head start in understanding the properties of coronavirus SARS-CoV-2. The unique structure of these viruses has enabled the development of a vaccine in record time through leveraging knowledge and technology platforms. There has also been unprecedented investment and research into vaccine development due to the COVID-19 pandemic.

There are various methods and approaches that are used to assess the effectiveness of vaccines. All of the globally authorised vaccines that are most advanced in their research, trials, and production use four different approaches, and here Wellcome Trust explains their differences. Whilst, this Johns Hopkins University resource explains the clinical trial process for vaccines.

All COVID-19 vaccines approved by the World Health Organization (WHO) undergo the same review and regulatory process, with safety and efficacy review boards composed of independent scientists not involved in vaccine development.

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What is the meaning of key vaccine-related terms such as herd immunity, susceptibility, vaccine efficacy, and viral mutations?

There are many words and phrases used to explain COVID-19 and vaccines. It’s important that key terms are explained so that people understand them.

Immunity - Immunity to a specific infection means that if someone gets that infection, their body’s immune system can recognise the infection and stop it before it causes disease. For example, if someone is fully vaccinated against COVID-19, it means that if they get the coronavirus SARS-CoV-2, their immune system will recognise it and destroy it, so it cannot cause severe COVID-19. Some level of immunity can also be gained from having the disease. This is often called natural immunity.

Susceptible/Unsusceptible individuals - Viruses, such as SARS-CoV-2, exist to reproduce and replicate. However, viruses need a susceptible host, someone who is not immune, in order to replicate. If a vaccinated, uninfected person is exposed to an infected person, the uninfected person is not a susceptible host. As a result, the virus will have a reduced ability to spread. If you have enough people within a community that are vaccinated and less susceptible, the virus dies out.

Herd Immunity - Herd immunity is the community protection that is created when a high percentage of the community is vaccinated, which provides a protective barrier to those who have not been vaccinated, or unable to be vaccinated (e.g., immune-compromised). Currently, the world has not reached herd immunity against COVID-19. This video – How does herd immunity work? – provides a practical explanation. For COVID-19, the coverage necessary to reach herd immunity remains unknown. However, data suggest the coverage level is between 70% and 85% of the population being fully vaccinated. As we have not yet reached this level, we cannot rely on herd immunity now. This makes it critical to promote vaccine uptake and continue to encourage preventive behaviours such as hand hygiene, appropriate mask-wearing, physical distancing, and covering coughs and sneezes. It is also essential that countries are equipped with the diagnostics to detect and test, track and trace contacts, facilitate the quarantining of cases and provision of medical care to those who are seriously ill.

Vaccine Efficacy - Vaccine efficacy is how effective a vaccine is at preventing infection and disease-related morbidity and mortality. Many different endpoints (comparison between vaccine candidates and within differing populations) are used in vaccine research to describe vaccine efficacy. In the case of SARS-CoV-2, an efficacious vaccine might prevent infection, disease, hospitalisation, intensive care unit admission, death, or transmission as per the figure below.

No vaccine is 100% effective at preventing infection. Current COVID-19 vaccines reduce the probability of infection by 90% (Pfizer & Moderna vaccines) in people who were fully vaccinated and 82% (Johnson & Johnson vaccine) to 100% protection (AstraZeneca vaccine) is provided against severe disease. Experts are still learning how effective COVID-19 vaccines are at stopping transmission of SARS-CoV-2. Recent research suggests that those given a single vaccine dose can reduce household transmission of the virus by up to half (vaccinated people are between 38% and 49% are less likely to pass on than unvaccinated people). Efficacy is also dependent on how many doses of a vaccine are needed. For a single-dose vaccine, our immune system will take a few weeks after vaccination to mount an antibody response to the vaccine. For a two-dose vaccine, both doses are needed to provide the best level of protection possible. The duration of protection from vaccines is currently unknown and we are less clear about how long natural immunity lasts. It is possible that in the future we may be offered ‘booster doses’ of COVID-19 vaccines which are designed to sustain protection for a longer period. But initial COVID-19 vaccine data suggests high levels of protection (+90%) of up to six months. For all vaccines, this is an important outcome and will continue to be monitored in the period following vaccination.

Variants & Mutations - Like all viruses, SARS-CoV-2, is mutating (changing in small ways over time). This is a normal evolutionary process and true of all viruses and other living things. Even with these mutations, it is still the same SARS-CoV-2 virus. The mutations that have arisen so far have meant that the virus can pass more easily between people, cause more or less severe illness, or slightly different symptoms. Globally, several variants have emerged, and these variants differ in their related morbidity and mortality. WHO, in joint collaboration with their global partners have assessed the evolution of SARS-CoV-2 and have characterised specific Variants of Interest (VOIs) and Variants of Concern (VOCs) in order to systematically prioritise the global monitoring and research, which is critical to the pandemic response. The simple, easy-to-say labels for the VOI and VOC can be found here. Proactive efforts are already in place in real-time to revise the vaccine to tackle vaccine variants and mutations. One advantage of the current vaccines is that they can be reconfigured quickly, and therefore will play an important role in responding to the variants.

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Want to learn more about integrating vaccine promotion into COVID-19 prevention work:

Written by: Jenny Lamb

Reviewed by: Lizzie McKee, Tom Heath, Victoria Maskell, Genevieve Hutchinson, Sarah Malycha, Rupali J. Limaye, Sian White, Daniel Korbel

Last update: 30.06.2021