(Photo by NICOLAS ASFOURI / bioreports) / TO GO WITH Health-virus-China-vaccine,FOCUS by Patrick Baert
Continued from yesterday
This is known as Antibody Dependent Enhancement (ADE) of infection. Antibody Dependent Enhancement of infection must be ruled out in every vaccine against coronaviruses. Let us note that SARS is caused by SARS-CoV and COVID-19 is caused by SARS-CoV-2 but they are both coronavirus. We must exercise caution in approving vaccines because if it gives a nasty side effect, people would be reluctant to get the vaccine. We must also note that the provision of a vaccine does not mean the disease is gone forever. People should remain responsible and respect COVID-19 protocols. Small pox is the only viral disease that was globally eliminated by vaccination. The vaccine against COVID-19 is not going to eradicate the disease but we all wish it will. If the vaccinated person is exposed to the virus, it is expected that the immunity developed from the vaccine will fight the virus successfully. People can still get infected but the vaccine will reduce the severity of the virus than if one had not been vaccinated. People that get infected may also be asymptomatic. However, if large populations were vaccinated against SARS-CoV2, we can achieve a level of herd immunity.
Even though the virus might be present, no one falls severely sick from the infection because of the herd immunity so that it appears that the disease is no longer present in the population. There are still so many unknowns about the virus. What type of immunity does an infection with SARS-CoV2 confer? Does COVID-19 give a three to six months immunity? Recent reports have shown that reinfection can occur with SARS-CoV-2 within a space of four and a half months. Such was the case of a 33-year-old man screened at Hong Kong airport. There were differences in the strains between the viruses in the first and second infections. The second infection was less severe than the first but that could have been because it was a different strain or it could be because of a primed immune response. The second infection was asymptomatic. The reports of reinfection with SARS-CoV-2are infrequent and inconclusive. By the 7th of September, there were 27.2 million cases and 18.2 million recovered cases. Only a handful of reinfections had been reported from a backdrop of 18.2 million recovered cases so it’s impractical to draw conclusions. The virus has only been on the world stage for nine months so it’s impossible to see if it confers a life-long immunity in some people. What type of vaccines are we using? What type of immunity will the vaccines confer? Is it going to give a seasonal immunity and we’ll need to be revaccinated every year? Is it going to be short term like six months or will it be five years then a booster dose like in tetanus? or will it be lifelong like in polio and small pox vaccines?
Traditional methods of vaccine development take years but use of genetic engineering has reduced the time it takes to develop a vaccine. Less than two weeks after informing the world of the viral disease, the Chinese published a sequence of the novel coronavirus. The quick publication of the virus genome by the Chinese has also reduced the time it takes in developing a vaccine. How do vaccines really work? Our blood has foot soldiers that once they recognize a disease pathogen and successfully fight it off, they will store the traits of that disease pathogen in their memory for future reference. If the same or similar disease pathogen enters the body again, they will neutralize it.
These foot soldiers are the antibodies. Vaccines stimulate the immune system to recognize specific proteins displayed on a target pathogen’s outer surface. A vaccine can be made from synthetic or natural proteins that are the weakened versions of the specific protein displayed on the pathogen’s surface. Candidate vaccines are created from different vaccine platforms and they all have their advantages and disadvantages. Since the genome of the virus has been published by China, researchers can create a DNA or RNA blue print of certain parts of the genome.
The DNA or RNA vaccine is able to stimulate the immune system to create antibodies or foot soldiers. RNA vaccines elicit a stronger immune response than DNA vaccines, therefore requiring a lesser dose. The disadvantage with RNA vaccines is that they are easily destroyed by body enzymes and need to be kept at an optimal low temperature which might become a challenge in hot climates like Africa or in regions where electric power supply is unstable. The DNA vaccines can withstand high temperatures. Another type of vaccine platform is using a cold adenovirus to introduce a DNA blueprint of the SARS-CoV-2 into the body. However, the adenovirus could be neutralized before it introduces the DNA blueprint and it may actually cause a disease on its own. To eliminate the adenovirus causing a disease, a non-replicating type that has been engineered is being used to introduce the DNA blueprint. It is called a non-replicating adenovirus. A third type of vaccine platform is a SARS-CoV-2 inactivated virus vaccine plus adjuvant.
The adjuvant increases the durability and response magnitude. Inactivated virus vaccines are the traditional type. A fourth type is the gene- based vaccines. They have never been produced on a commercial scale for a human illness. They have been produced and used in laboratories. A fifth type of vaccine platform is the protein subunit. A specific protein is isolated from the virus and the protein will elicit antibodies. Unfortunately, sometimes it may not elicit the antibodies that will neutralize the virus.
A protein subunit vaccineis safe because it does not have any live components and therefore cannot cause COVID-19. A more recent vaccine platform is the plant derived virus like particles (VLP).Virus like particles have structures resembling viruses but because they lack the viral genome, they are non-infectious, can stimulate the immune system and so make good vaccine platforms. They mimic the outside structure of a virus but are empty inside, devoid of any viral genomic material. They can occur naturally and can also be synthesized. The advantages of VLP vaccines is in their safety and ability to elicit an immune response. Since VLP do not have a genetic material, they cannot replicate which makes them safe. The downside to VLP is in the time it takes to manufacture them and costs. Some hepatitis B and human papilloma virus vaccines are from VLP.
The candidate vaccines that have reached Phase III clinical trials are using any one of the vaccine platforms already described in this column. Until the candidate vaccines are approved, no one is sure which of them will work and if they can be produced in billions. Our Governments should wade through all the hype surrounding the race to COVID-19 vaccines and stay informed on their advantages and disadvantages before making a choice. They should not be in a hurry to use any of the myriad of vaccines that would eventually become available. While the king in the lion and the jewel got his bride, when it comes to vaccine, caution is king and the vaccine is the jewel. The two must always go hand in hand.
Obilade, (Phd), teaches public health in a private university in Abuja.