Immunity & coronavirus vaccine development. The coronavirus belongs to the coronoviridae family of the viruses. These viruses cause mild to lethal respiratory tract infections in humans. The novel coronavirus (virus in this write up) is a member of coronaviruses. Here, we will briefly discuss the process of adaptive immunity and coronavirus vaccine development.
In case of the virus the acquired immunity is activated in the following pattern:
- The virus makes contact with the host cell. The spike protein on the surface of virus is locked onto the ACE 2 receptors on the surface of host human cell.
- The virus enters the cell, fuse with vesicle and its RNA is released.
- Viral RNA uses the protein machinery of host cell. Sub-genomic mRNAs are synthesized and structural and not structural proteins are translated. In this way multiple copies of virus are assembled and released from cell. These viruses in turn attack other host cells.
- Immune response starts. The antigen presenting cell (APCs) engulf the virus.
- The APC displays a portion of the virus to T-helper cells.
- T-helper cell generate two main immune responses.
- B cells are provoked. The B cells in turn make antibodies. The antibodies serve two functions. They may block the entry of virus in to other cells or may destroy the virus.
- Cytotoxic T cells are activated. These cells engulf and destroy the virus.
- This response is memorized by the immune system of the body. T and B cells keep on patrolling inside the body. A quick immune response is generated if 2nd time the virus invade the body.
Types of vaccines
The pattern of the adaptive immunity is used for the development of vaccine. The viccinologist opt any of the following methods for the development of vaccine against the virus.
- A harmless virus, e.g. adenovirus, is modified by insertion of a part of RNA of coronavirus in the genome of it. This part of RNA is capable of translation in to one protein. The RNA of the coronavirus makes only one type of protein and against this protein immune system is provoked. No coronavirus is assembled. The immunity developed in this way serve the protection of the body if coronavirus enters the body from outside. This type of vaccine is called viral- vector vaccine.
- A part of RNA of coronavirus is directly inserted into host cell. This part translates for a specific protein and immune system is activated. This type of vaccine is called RNA vaccine.
- The protein of the virus is directly injected into human cell and the immune system is provoked. This type of vaccine is called protein vaccine.
- The disease causing virus is killed or inactivated. The disease causing property of the virus is made non-virulent however the immune system provoking capability is retained in the virus. These inactivated viruses are used for the provocation of immune system. This type of vaccine is called virus vaccine.
After opting any of the aforementioned 4 methods for the development of vaccine, the vaccine developing company first presents the proposal to FDA. After getting the approval from FDA for the development of vaccine the vaccine is prepared and before its approval against any disease the vaccine is trialled in these phases.
- Preclinical trial: Before the testing on human the vaccine is tested on laboratory animals for the monitoring of safety and efficacy of vaccine.
- Phase 0 trial: A very small dose of vaccine is administered on a small number of people, usually 10. In this trial the harmful effects of the vaccine is monitored and if found, corrected.
- Phase 1 trail: This trial is done on 20-50 healthy people. In this trial the highest dose of the vaccine without any side effect is identified. So in this phase the safety of the vaccine is monitored.
- Phase 2 trial: This trial is done on a sample size of few hundred participants who are living with or without the conditions that the new vaccine is meant to treat. They are given with the same dose which are given in phase 1 trial. This trial is done for testing the safety or efficacy or both.
- Phase 3 trials: The number of participants for this trail may be kept more than 3,000 living with the condition that the new vaccine is meant to treat. This trial is done for testing efficacy.
After successful phase III trial of coronavirus vaccine is approved by FDA and commercialised. Many companies may modify this pattern or may conduct phase II and III trials simultaneously. In these phases randomization may be done in which the subjects exposed to vaccine is monitored in relation to control group.