The most advanced vaccine projects, including those at the University of Oxford and the US pharmaceutical company Moderna, are heading for large-scale phase III trials in which side effects or less common safety concerns are expected. become apparent.
Side effects are common and can cover a wide range of illnesses, most of which are unwanted but not a significant barrier to receiving a vaccine. Some, however, may be so rare that they do not appear until a vaccine is population-wide.
Maurice Hilleman, an American microbiologist who has developed more than 40 vaccines, is said to have claimed that he did not relax until the three millionth dose of a new vaccine had been administered.
This was not without reason – these rare side effects can be serious. The 1976 case is one example, as is Pandemrix, a swine flu vaccine given to around six million people in the UK in 2009-10. It has been found to cause narcolepsy, a debilitating sleep disorder, in about one in 55,000 people vaccinated in the UK, or just over 100 people.
The classic example, said Professor Naor Bar-Zeev, an infectious disease physician and statistical epidemiologist at the Johns Hopkins University International Vaccine Access Center, is that of RotaShield, a vaccine against rotaviruses that causes diarrhea. released on the American market in the late 1990s.
The vaccine has been linked to a very small number of cases of intussusception, a potentially fatal bowel disorder, and was quickly withdrawn from use. A replacement was not available for nearly a decade and during that time, Prof. Bar-Zeev said, “several hundred thousand children have died from diarrheal diseases which would have been prevented if this so-called” bad “Vaccine had been available”.
The key point, he added, is that “despite their phenomenal contribution to health, all vaccines carry a certain risk and it is a societal decision, an ethical decision and a political decision on the right balance of risks, and this balance really depends on local circumstances ”.
He said: “The world is already suspicious of vaccines, and we cannot spread a vaccine around the world if it causes damage. Even though these damages are very limited and even though, as expected, the benefits far outweigh the risks, these risks still need to be very clear so that people are fully aware of what they are doing and understand. by themselves the balance between benefits and risks. ”