Vaccines: our best line of defense against infectious diseases like COVID-19

Inside vaccines

Vaccines train the immune system to identify and eliminate germs that attack the human body.  

Vaccine solutions contain different elements related to the targeted pathogen, a “microorganism” or “germ” that can cause disease. These different elements can include either whole pathogens that are attenuated (weakened) or that are inactivated (essentially killed).  Some vaccines use only portions of the pathogen such as proteins on its surface that have been isolated and reproduced. There are even newer technologies under development that employ just the genetic coding of the portion of the pathogen.

“Today Sanofi is working with two different technologies in its pursuit of vaccines for COVID-19. The first is a recombinant protein technology which uses, among other ingredients, portions of the ‘spike protein’ on the virus’ surface. The second is an mRNA technology that includes the genetic coding for the spike protein. The expectation in both cases is that the body can be trained to more quickly identify the virus and combat it because it has already ‘seen’ and eliminated the spike protein, thanks to our vaccines,” notes Triomphe. 

How vaccines work

Indeed, vaccines essentially trigger the immune system to react as if there was a pathogen present, but without causing illness. 

For nearly 150 years, vaccines have provided high levels of protection, sometimes with just one shot, using live attenuated whole viruses such as in the yellow fever vaccine which provides 99% protection from the deadly infection. Smallpox, once a terrifying disease, has been eradicated thanks to this kind of vaccine. On the flip side, live attenuated viruses tend to cause a greater number of side effects than newer vaccine technologies, although these reactions are usually minor (a headache or slight fever). 

Newer technologies can deliver strong protection, while becoming even more tolerable. One example is the inactivated polio vaccine, which provides nearly 100% protection with a series of vaccinations. This approach has helped relegate polio to just a handful of countries worldwide, preventing countless children from ever seeing this truly horrific disease. 

However, the remaining diseases against which scientists still seek to develop vaccines are more challenging, caused by viruses that are more complex and trickier to prevent.

One of these viruses is HIV, the virus that causes AIDS. HIV mutates drastically and rapidly even within a person, making it difficult for scientists to target any portion of it in the development of a vaccine. By the time the immune system identifies HIV, the virus has changed shape to appear “foreign” again, then continues attacking cells at alarming rates, all the while leaving the body vulnerable to infection and its deadly consequences.  

Certain influenza strains mutate with less frequency than HIV, but still enough to require annual vaccination, often with new formulations to match the specific virus types that circulate each year.  

“Fortunately, so far, scientists have found that the pandemic-causing SARS-Cov2 that has caused COVID-19 disease does not mutate frequently nor in ways that could render vaccine development more challenging. This is one of the reasons why scientists are relatively optimistic about vaccine development,” says Triomphe.

Protection of entire populations

Once governments approve new vaccines for use, it’s typically important to vaccinate as many people at-risk for the targeted disease as possible as well as those who can still transmit the disease. 

“Broad vaccination can serve to help grow the immunity levels of an entire population. In other words, when a large majority of a population has either had the infection recently or has been vaccinated, the pathogen cannot find enough bodies that it can infect in order to survive, replicate and move on. At a certain point the virus dies, eliminated by a person before it can find another,” explains Triomphe. This is how epidemics, even pandemics, can more quickly subside or in some cases, become eradicated. 

Could that be the final destiny for SARS-Cov2? While this is the hope of thousands of researchers already working on vaccines, it’s too early to know for sure. Concludes Triomphe: “What is certain in this unsettling time is that the potentially powerful intervention of vaccines remains undoubtedly the best hope for beating back COVID-19.”