The worldwide coronavirus crisis has seen vaccine developments surge. According to the vaccine alliance Gavi, 170 different vaccines have been in trial during the pandemic.
There are more vaccine candidates in the pipeline for COVID-19 than ever seen before for an infectious disease. These vaccines all want to achieve coronavirus immunity with some being able to possibly halt transmission.
According to Gavi, vaccines stimulate an immune response to an antigen, which is a molecule found on a virus. With COVID-19, the antigen is usually a “characteristic spike protein found on the surface of the virus, which it normally uses to help it invade human cells.”
Recent months have seen several announcements from different pharmaceutical companies stating that the vaccines they have been engineering have reached high levels of efficacy.
The companies are:
- Pfizer and BionTech
- Sputnik V
- Oxford University and AstraZeneca
According to Gavi, vaccines can be divided into four categories within clinical trials:
- Whole virus: This is the conventional vaccine which uses the virus in its entirety to trigger a human immune response. This is done by using vaccines with a weakened or inactive virus which can still be replicated without causing sickness but can cause an immune response. These vaccines usually require cold storage specifications.
- Nucleic acid (RNA or DNA): This vaccine uses genetic RNA or DNA material to assist cells with creating antigens. In the COVID-19 vaccine, the spike protein which is responsible for making an individual ill, will be used to enter cell protein factories to make antigens which will trigger the immune response. These vaccines are lower in price and easier to make since the antigens are created within human cells in large quantities, the immune responses are usually strong. However, DNA and RNA vaccines have yet to be licensed for use, making it difficult to obtain regulatory approval.
- Viral vector: These vaccines send ‘instructions’ to cells in order to produce antigens. However, they differ from Nucleic acid vaccines by using a ‘harmless’ virus which is different from the virus which the vaccine targets, in order to deliver the instructions. These vaccines may mimic natural viral infections which will trigger strong immune responses. Individuals who have already been exposed to the viruses used in the viral vector vaccine may already be immune to it, making it less effective.
- Protein subunit: This vaccine uses pathogens (such as protein fragments) which trigger a response from the human immune system. This minimizes the risk of side effects, but may result in a weaker immune response. These usually require immunological or pharmacological agents to boost the immune response such as the Hepatitis B vaccine.
The specifications of the four vaccines are as follows: