7-13 décembre 2020
Vaccination without risks ?
The first results of clinical trials around the world have come in: the new year will bring widespread vaccination of at-risk populations against SARS-CoV-2, the virus responsible for COVID19. While the FDA (the American authority which oversees the commercialization of medicinal products) and other national bodies are beginning to give their consent for the first anti-COVID-19 vaccinations, ensuring the safety of these vaccines remains a priority.
Vaccination is of course one of public health’s greatest success stories. It is estimated that it helps us avoid some 6 million deaths per year. It has led to the eradication of smallpox and the quasi-eradication of polio, while considerable reducing cases of measles. Vaccines have also had some success against viruses that cause hepatitis A and B, flu, the papillomavirus (which can lead to cervical cancer) and others.
However, this global success has gone hand in hand with undesirable side-effects. In 1995 a batch of polio vaccines using an untested inactive virus led to symptoms such as headaches, fever and muscular weakness in more than 40 000 people, as well as causing permanent paralysis in 51 people and the death of 5 others. How can this be explained? In fact, the virus in question was still active. This event led to the creation of new regulations in order to guarantee the quality of each batch of vaccines put on the market.
Understanding the protective mechanisms of each type of vaccine allows us to guarantee optimal protection while avoiding undesirable immune responses or the development of illnesses. For example, a vaccine developed in the 60’s against a chemically inactive virus, the FI-RSV, did lead to increases in the number of antibodies in people having received the vaccine, but in reality did not protect against infection by the virus. Vaccinated children actually ended up in a more severe condition than others who had fallen ill through the virus.
It’s also important to alert public health authorities when undesirable side effects are seen even rarely during clinical testing. For example, at the time when the first anti-rotavirus vaccine was developed in 1998, (this virus causes potentially fatal episodes of diarrhea in children), a particularly painful intestinal obstruction appeared, fatal in 5 out of 10 000 cases where patients had been treated with the vaccine, compared to 1 patient out of the 4600 participants in the placebo group. This was considered to be an insignificant statistic at the time, but the result was about ten pathological cases when the vaccine was put on the market.
The story of vaccination reminds us of the importance of strict sanitary controls during and after trials. While there is clearly a very high demand for vaccines against SARS-CoV-2, it’s imperative that strong security standards be maintained, that clinical protocols are followed closely throughout vaccine development, and that data is collated on the vaccine’s effects (immunogenicity, protection, effectiveness and durability) before and (obviously) after the product is put on the market.