Vaccines have been used for more than two centuries to protect people from disease. All vaccines are designed to work in more or less the same way; to trigger an immune response in the host that is directed specifically against some microbial invader. This response primes the immune system and allows for a more rapid, sustained, and efficacious reaction. In the past, most vaccines used killed or weakened microbes as the agent to set off immunity. Usually, proteins on the surface of these pathogens are recognized as foreign substances, causing the immune response to kick in. More recently, individual proteins or parts of proteins that make up the invading pathogen have been employed for the same purpose.
All three of the candidate vaccines that have recently shown efficacy and safety in phase III trials aren’t protein based. They’re either made from RNA (Moderna and Pfizer) or DNA (AstraZeneca), molecules that are not proteins themselves but are intended to direct the synthesis of one of the pathogen’s proteins inside cells of the vaccinated individual. These nucleic acid based vaccines have two great advantages over the more traditional ones. First, they can be easily modified so that the protein that they can specify whatever protein is desired. And second, they can be synthesized quickly in great amounts.
These advantages are critical, especially in a pandemic. Pandemics arise rapidly. The current one, Covid-19, began in early 2020. In less than a year, it has infected nearly 60,000,000 people globally and killed over 1,400,000. It appears that many more will contract the disease and die. Traditional vaccines take years to develop. Many are difficult to deliver in large quantities. Nucleic acids however, can be synthesized rapidly at an industrial scale. What’s more, once a facility has been set up to produce a nucleic acid based vaccine, the sequence of its DNA or RNA can be quickly changed so that an entirely different protein can be made in the same facility.
Nucleic acid based vaccines represent a triumph of molecular biology. The tools that are available to the current generation of practitioners in the field as well as the skill with which they use them boggles the mind. As of this writing, none of the three candidate vaccines have yet been approved for release to the general public, but such approval is expected within weeks. However, if they are as successful as initial tests indicate, they will save thousands of lives. What’s more, they promise to be able to be used as weapons against other diseases, such as cancer. Their rapid development represents a breakthrough in the prevention of disease.