Last updated on April 24, 2020
Last week, we went through some of the science of viruses: how they infect, how they evolve, and how they can make the jump from one species to another. This week, I want to touch on some of the ways the medical field combats viruses, such as with vaccines, used to promote immunity, and anti-viral drugs, used to treat viral infections and reduce their severity. In the past few months, researchers around the world have been scrambling to produce a vaccine or anti-viral treatment to curb the spread and mortality rate of Covid-19, producing results at record breaking speeds. But as some of these drugs enter the first steps of clinical trials, it may be many months before they can be widely distributed in any meaningful way.
To understand vaccines, it is first necessary to understand how our immune system works on its own to combat infections. The immune system is able to recognize foreign invaders, antigens, because their surface molecules are different from the normal proteins on the surface of cells belonging to the body. This is the same reason why organ transplants can be rejected; another person’s organs have unrecognized surface proteins so the immune system can treat the new organ cells like an antigen. Once the immune system recognizes that there is a foreign invader, it has multiple lines of defense in place for neutralizing it. One of the most important lines of defense is the immune system’s production of antibodies.
Antibodies are created by specialized immune cells called B-cells. When a B-cell binds to the surface of an antigen, it matures and divides into a group of cells that construct and secrete millions of antibodies into the bloodstream. These antibodies are specifically tailored to bind to the antigen. The binding of an antibody to an antigen can prevent the antigen from infecting cells and/or can recruit other immune elements to destroy the antigen completely. This process can take several days though. In the meantime, the immune system has to resort to more brute tactics like inflammation and fever to combat antigens.
But you don’t get sick every time you come in contact with a particular pathogen. Anyone who has had chickenpox as a kid knows that, once you’ve been infected with it once, you are unlikely to ever get it again (this is the premise behind the frankly disturbing idea of “chickenpox parties”). When the immune system succeeds in defeating an antigen, a portion of the B-cells turn into Memory B-cells. These cells remain active in your body for a long time after the first infection; the second time the same antigen attacks the body those Memory B-cells create the proper antibodies much faster and in a much higher quantity than the original defense. This mechanism allows for people who have been infected by a pathogen to remain functionally immune to reinfection for a period of time.
Vaccines leverage this immunity mechanism to make your body generate these Memory B-cells for a certain pathogen without exposing you to the danger of a full infection. In the case of viruses, there are three main types of vaccines: live, attenuated vaccines; inactivated vaccines; and subunit vaccines.
Live, attenuated vaccines are made from live pathogens that are weakened substantially before being injected in a patient. The Measles, Mumps, Rubella (MMR) vaccine is an example of a live, attenuated vaccine. It took nearly 10 years of tissue culturing for researchers to weaken the virus enough to make a safe vaccine. Live, attenuated viruses have to replicate themselves inside the body, in order to incite an immune response, but they are not strong enough to put up a proper fight that might make you sick. However, these vaccines shouldn’t be used in individuals with suppressed immune systems. Without proper, functional immune responses, even the weakened virus found in a live, attenuated vaccine could grow unchecked.
Inactivated vaccines are made by pathogens that have been killed by heat or chemicals before being injected into the patient. These pathogens are completely dead, cannot replicate, and cannot make you sick, even if you are immunodeficient. These vaccines don’t create an immunity that is as strong or long-lasting as the live vaccines, so they often require multiple boosters that are spaced out. Inactivated vaccines often have added adjuvants, chemical additives like aluminum salts, which can increase the vaccine’s effectiveness and help to strengthen your body’s immune response. The adjuvants are also the reason why a side effect of some vaccine injections is muscle soreness around the injection site. The polio (IPV) vaccine is an inactivated vaccine that is usually given to children four times before they are 6 years old.
Subunit vaccines are made of only the parts of the pathogen that the immune system recognizes as an antigenic foreign invader. In some cases, this can be a protein receptor found on the surface of the pathogen. Protein subunit vaccines have been developed for Hepatitis B and Human Papillomavirus (HPV). The challenge with these vaccines is identifying what pieces of the virus are sufficient to prompt an immune response. Like the inactivated vaccines, they don’t usually produce long-term immunity like the live, attenuated vaccines, and they are often used with adjuvants to increase their effectiveness.
Some subunit vaccines use DNA or RNA that encode for antigenic proteins on the virus surface. The idea of these vaccines is that, following injection, the genetic material will be taken up by the cell and translated into the antigenic protein. Although researchers have been interested in these types of vaccines since the 90s, RNA vaccines are only just starting to make it into clinical trials. The appeal of these types of vaccines is that they are relatively easy to manufacture, and there is already a manufacturing infrastructure in place to produce RNA.
I hope you’ve learned a lot about vaccines in this week’s blog post. Next week, I will write more about anti-viral drugs and the ways doctors can help your immune system combat a viral infection. After that, I will write more about the vaccines and anti-viral solutions that are entering clinical trials for prevention and treatment of Covid-19. Comment below or email me at contact@anyonecanscience.com to let me know what you think about this week’s blog post and tell me what sorts of topics you want me to cover in the future. And subscribe below for weekly science posts sent straight to your email!
