How do vaccines work? A response to questions raised by our members
How does the immune system work?
The Immune System is a complex system of proteins, cells and organs that work together to protect us from outside invaders such as bacteria, viruses, fungi, parasites and toxins.
There are two parts to the immune system, the innate immune system (which we are born with) and the adaptive immune system, which learns about infections and protects in the future. The innate system is the body's rapid response system. It has no memory and is a nonspecific response to the infection. Its function is to send out chemical messages to attract immune (white) cells to the infected area. These cells then produce nonspecific antibodies which coat the infecting virus and make it available for removal by other white cells (B-lymphocytes).
The adaptive immune system is different in that it remembers past infections and produces specific antibodies to neutralise the infecting virus. This is a slow response. After an infection the body keeps a few memory cells (T-lymphocytes) around so that the next time an infection occurs these cells form part of the rapid response and stop the infection before it can become established.
What are vaccines and how do they work?
There are several types of vaccine.
- Vaccines are made from inactivated or killed virus. These vaccines contain dead or inactivated virus. When this is injected our bodies recognise this as foreign and make B and T-lymphocytes that will remember how to fight the virus if we become infected in the future. The US Centers for Disease Control and Prevention (CDC) has provided a simple description of the modern vaccines that are being made.
- Vector vaccines1 contain a modified version of a different virus from the one that causes COVID-19. Inside the shell of the modified virus, there is material from the virus that causes COVID-19. This is called a "viral vector". Once the viral vector is inside our cells, the genetic material gives cells instructions to make a protein that is unique to the virus that causes COVID-19. Using these instructions, our cells make copies of the protein. This prompts our bodies to build T-lymphocytes and B-lymphocytes that will remember how to fight that virus if we are infected in the future.
- mRNA vaccines contain material from the virus that causes COVID-19 that gives our cells instructions for how to make a harmless protein that is unique to the virus. After our cells make copies of the protein, they destroy the genetic material from the vaccine. Our bodies recognise that the protein should not be there and build T-lymphocytes and B-lymphocytes that will remember how to fight the virus that causes COVID-19 if we are infected in the future.
- Protein subunit vaccines include harmless pieces (proteins) of the virus that causes COVID-19 instead of the entire germ. Once vaccinated, our bodies recognise that the protein should not be there and build T-lymphocytes and antibodies that will remember how to fight the virus that causes COVID-19 if we are infected in the future.
Some vaccines require two doses, and some require only one. The second dose is usually at least 21-28 days after the first and boosts the immune response started by the first. The optimal timing of the second dose of some COVID-19 vaccines is being debated and may be 12-16 weeks after the first.
Some vaccines prevent infection from happening while some prevent the disease from becoming serious.
Why are there side effects and what are they?
Vaccines work by fooling the body into thinking that it is infected. This simulates an infection and the most common side effects are those of a mild infection: fever, body aches and pains, headache, and local soreness at the injection site. These usually appear within a few hours or days after the injection and are gone within 2-3 days.
There may be allergic reactions to vaccines, but these are extremely rare and are usually caused by substances added to the vaccine to stabilise it or preserve it. Most people have no side effects at all.
Which vaccines will be available in South Africa?
At present there are two vaccines that are going to be used in South Africa. The first is manufactured by Johnson and Johnson. This is a vector vaccine that uses a virus that cannot cause disease in humans and that has been modified to give cells the instruction for the spike protein of the virus that causes COVID-19. It is given as a single dose and has been shown to be very effective in preventing severe disease and 100% effective in preventing death from the infection.
The second vaccine is an mRNA vaccine made by Pfizer-BioNTech. This vaccine is given as two doses and is also highly effective.
The vaccination programme and the purchase of vaccines is controlled by the South African government and is based on advice from the World Health Organization. There are three phases, the first of which is to vaccinate those most at risk and then progress through the population based on an assessment of vulnerability to the infection. Details of the vaccine rollout can be found on the Department of Health Website: https://sacoronavirus.co.za/vaccine-updates/
What are variants and do the vaccines protect against them?
Viruses change constantly though mutation and new variants are expected over time. Some variants emerge and disappear, others emerge and stay. They can make the virus more infectious, more virulent or equally, less infectious and less virulent. Multiple variants of the virus that cause COVID-19 are circulating in the world but several have become more prominent. A variant called B.1.1.7 was found in the UK in the latter part of 2020 and has been found to be more infectious and possibly associated with an increased risk of death. Another variant B.1.351 emerged independently of the UK variant and has become the dominant strain in South Africa. This variant seems to be more infectious. A third variant, called P1 was identified in Brazil. In addition, there are new variants in New York and California that are causing some concern. All of these variants have now been found in multiple countries, carried by travellers.
Both the Pfizer vaccine and the J&J vaccines have been tested against the South African variant and found to be effective.
Our appreciation to Dr Frank Fox, member elected Trustee of the Scheme, for his contribution to MediBrief by providing this article.
Published: March 2021