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New things are easily seen as something to be afraid of. For example, why should the completely new RNA vaccine technology be used against COVID-19 when there are more traditional ways to produce vaccines that have been used for a long time?

There are two key requirements for vaccines: they must be effective and as safe as possible. The benefits of vaccines are seen at the population level, but any adverse effects are experienced by individuals. Furthermore, adverse effects are not necessarily experienced by the same people who experience the benefits. Severe adverse effects are therefore regarded as utterly unfair, even if the vaccine has undeniable benefits in relation to its adverse effects. New types of vaccines enable us to produce vaccines that are safer than before.

Traditional vaccines contain live or dead viruses

For a long time, people have been aware of the fact that, in the case of most diseases, infection protects against future infection. Vaccination is a safer way to produce the same effect. Edward Jenner’s breakthrough was to use the less dangerous cowpox virus instead of the smallpox virus.

He proved the efficacy of the vaccine in an exposure test. An eight-year-old boy who had been infected with cowpox was inoculated with smallpox excretion to prove that he had become immune to smallpox. In other words, the idea of using exposure tests to prove the efficacy of vaccines is nothing new.

Jenner’s idea to use the cowpox virus, which is less dangerous than the smallpox virus, to achieve cross-immunity continues to be reflected in our vaccination programme. The less dangerous Mycobacterium bovis bacterium is used instead of the Mycobacterium tuberculosis bacterium in the BCG vaccine, which (partly) protects against tuberculosis. However, the use of live pathogens involves a risk, particularly for people with a reduced immune response. In the worst case, the vaccine can cause them to develop the disease.

Making the virus less dangerous has been an effective way of preparing vaccines. Vaccines containing such viruses typically provide very good and long-term protection. For example, the MMR vaccine – which is used against measles, mumps and rubella – is effective and known to cause very few severe adverse effects, based on decades of use experience. Vaccines containing ineffective or dead viruses are widely used. Many of the coronavirus vaccines developed in China have been prepared using this method.

This being the case, why have Western vaccine researchers set out to develop coronavirus vaccines using new technologies that may involve risks?

New vaccine technologies aim for vaccines that are as safe as possible

The key goal for new types of vaccines is to make them as safe as possible. Because RNA vaccines do not contain any live or dead viruses, they cannot cause anyone to be infected with COVID-19 in any way. There is no risk of failing to make a virus ineffective, and a person without immunity cannot be infected by a weakened virus.

The RNA vaccine is the most simplified type of vaccine. Inside a lipid film, it contains a short piece of code, RNA, which enables the cells of a vaccinated person to produce the part of the virus that their immune response is targeted at. In other words, they are not exposed to the complete virus. Because the immune response thus created only concerns a specific part of the virus, the probability of undesired effects is as small as possible. The RNA contained in the vaccine degrades in the body rapidly, meaning that it has no long-term effects on the vaccinated person.

In other words, compared with traditional vaccines, safety is the key benefit of RNA vaccines. I used to wonder whether such vaccines were sufficiently effective. The recent good news about coronavirus vaccines has shown that my doubts were unfounded. Both RNA vaccines have a protection efficacy up to 90% against symptomatic COVID-19 after the second dose, and the vaccines have also proved to be effective among people aged over sixty-five. Vaccine protection gradually fades but remains good for most at least six months. The third dose returns excellent protection.

Jenner proved the efficacy of his smallpox vaccine in an exposure test. If the key issue with RNA vaccines was related to their protection efficacy, wouldn’t it have been enough to study their protection efficacy in an exposure test with volunteers?

Careful studies on potential adverse effects are required to get marketing authorisation

The current requirements for vaccines are extremely strict, particularly in terms of safety. In principle, the immune response triggered by a vaccine can also be harmful. Studies on even the most promising vaccines must therefore progress one phase at a time. First, the vaccine response is studied in a few dozen subjects. Any adverse effects are monitored closely at the same time. 

If the desired immune response is achieved and there are no severe adverse effects, the study can be expanded into the second phase, during which the vaccine is studied in hundreds of subjects. At this stage, in addition to healthy working-age people, members of the actual target groups – such as people aged over sixty-five in the case of coronavirus vaccines – can also be included. 

In other words, the potential adverse effects of the vaccine have been studied in hundreds of adults before the beginning of the studies on the efficacy of the vaccine. These studies, also known as Phase III trials, involve tens of thousands of participants, meaning that we can form an understanding of the adverse effects of the vaccine based on a considerably large sample. Obtaining a marketing authorisation requires that the benefits of the vaccine are indisputably more significant than its potential disadvantages.

Mika Rämet

Professor of Paediatrics and Experimental Immunology