Everybody is waiting for the Covid-19 vaccine. But will a vaccine alone be enough to stop the pandemic and allow life to return to normal? The answer depends on a how “good” the vaccine ends up being.
In a study published on July 15 in the American Journal of Preventive Medicine, computer simulation of every person in the US was used to show how effective a vaccine would have to be and how many people would have to get vaccinated to end the pandemic. It was found that a coronavirus vaccine’s effectiveness may have to be higher than 70% or even 80% before one can safely stop relying on social distancing. The measles vaccine has an efficacy of 95-98%, and the flu vaccine is 20-60%. That doesn’t mean a vaccine that offers less protection would be useless, but it would mean social distancing in some form may still be necessary.
Some have suggested that society will return to normal soon, especially if a vaccine becomes available by the end of the year or early 2021. This timeline is very optimistic and it is important to remember that a vaccine is like many other products: What matters is not just that the product is available but also how effective it is. Similarly, different vaccines may offer different levels of protection.
Since Covid-19 vaccines are still under development, now is the time to set vaccine efficacy levels to aim for, as well as to manage expectations. Running computer simulations is really the only way to ethically do this.
The PHICOR team at the City University of New York Graduate School of Public Health and Health Policy, working with scientists from the National School of Tropical Medicine at the Baylor College of Medicine, developed a computer simulation model of the entire United States and its population interacting with each other. Using that model, the team was able to introduce the Covid-19 virus into a virtual population in different ways and have it spread from person to person in various pandemic scenarios. Each simulated person who gets infected has probabilities of being hospitalised, placed on a ventilator or dying based on the severity of the problems just as in the real world.
Experiments using this simulated population can represent the different vaccines and what is likely to happen if different proportions of the population are vaccinated at different times during the pandemic. The results show how vaccines with different levels of efficacy would affect the pandemic and can be used to estimate the impact on things such as number of people who get infected, health outcomes and costs. In this case, we assumed that only one vaccination would be required.
Typically, in a pandemic, as more people are exposed to the virus, the number of new infections per day steadily increases until it reaches a peak and begins to drop. To stop the pandemic, the number of new infections per day needs to drop to zero, or at least to a very low number, as quickly as possible.
If the Covid-19 pandemic was just beginning and the population infected was close to 0%, the simulations show that vaccine efficacy would have to be at least 60% to stop the coronavirus if the entire population was vaccinated. Given the number of susceptible people who couldn’t be vaccinated because of age or health problems and the number who would refuse to be vaccinated, that’s probably impossible. If only 75% of the population gets vaccinated, the vaccine efficacy would have to be around 70%. If only 60% of people get vaccinated, the threshold goes even higher, to around 80%. It’s all about making sure the virus can’t find more people to infect.
These numbers assume that a person infected with the virus infects 2.5 other people on average. If the virus is more contagious, the vaccine has to be more efficient. Now, the further along the pandemic is, the less the height of the peak can be reduced. It’s like climbing a mountain – you are already at a certain height. Plus, it is harder to shut a pandemic down when there are more infectious people running around.
So, when 5% of the population has already been infected with the virus, the best that you can do is reduce the peak by around 85%. The difference between 0% and 5% can add up to millions of infections.
Vaccination Numbers Crucial
Based on these findings, a vaccine with an efficacy as low as 60% could still stop the pandemic and allow society to return to normal. However, most if not all of the population would have to be vaccinated. This seems unlikely. With fewer people protected, a vaccine would have to have an efficacy of at least 80% to be able to stop the pandemic by itself, meaning social distancing could be completely relaxed.
Again, all of this doesn’t mean that a vaccine with a lower efficacy would not be useful. It would mean that social distancing and mask-wearing likely would have to continue until the pandemic runs its course or a vaccine that is actually “good enough” arrives.
(The author is Professor of Health Policy and Management; City University of New York; www.theconversation.com)
Resistance from Within
To conquer the coronavirus, we first need to understand how our immune system reacts to it. The immune system is a network of intricately connected cells to protect the body from internal and external threats. It is broadly classified into two sub-types: innate (or natural) and adaptive (or acquired).
The innate system is the first line of defence, capable of detecting many common infectious agents, such as viruses and bacteria, as soon as they find their way into the body. Although it may respond quickly, the innate system cannot always eliminate infectious organisms and it doesn’t recognise all the pathogens. Because of the intricate nature of the immune system, the innate system also provides cues in the forms of chemical signals (cytokines) or degraded products of infectious organisms (antigens) to activate the adaptive immune system, using a process known as “antigen presentation”. Without these cues, the adaptive immune system cannot be activated.
The adaptive immune system has evolved to provide a more versatile and highly target-specific defence with an ability to distinguish very subtle differences in the make-up of infectious agents. But the adaptive immune system is slow and can take several days before two key cell types – B cells and T cells – are brought into play. T cells are further grouped into two sub-types, CD4+ and CD8+ cells. CD4+ are helper T cells that help the activity of other immune cells by releasing cytokines. The cytokines prime the maturation of B cells, which become plasma cells and produce antibodies to neutralise the pathogen. CD8+ cytotoxic T cells, on the other hand, directly kill infected cells.
Once the adaptive immune system has vanquished the invader, a pool of long-lived memory T and B cells are made. These memory lymphocytes remain dormant until the next time they encounter the same pathogen. This time, though, they produce a much faster and stronger immune reaction. Memory is the key feature of the adaptive immune system, enabling long-term protection. Since most people have not been exposed to the novel coronavirus, it can safely be assumed that uninfected people have no memory T and B cells and, therefore, no protection from a Covid-19 infection. Technically speaking, as with any other infection, Covid-19 should generate an immune response, priming the proliferation of anti-Covid T and B cells.
(The author is Lecturer in Immunology, University of Essex. www.conversation.com)
Over 140 coronavirus vaccines are being tested around the world, according to the World Health Organization. Here are a few on which hopes are riding:
Being developed by Chinese company, the vaccine is based on inactivated Covid-19 particles. It has shown a promising safety profile in the early stages of testing and its Phase 3 trials started on Jul 21 in Brazil.
Wuhan Institute of Biological Products and Beijing Institute of Biological Products are developing their vaccines in collaboration with Sinopharm, also in Phase 3.
University of Oxford/AstraZeneca
Preliminary data from Phase 3 trials show it is safe and induced a strong antibody response in all vaccinated volunteers, suggesting that an effective vaccine could be within reach. This trial was the first time that the vaccine was given to humans: 543 healthy adults aged 18-55 were vaccinated with a single dose of ChAdOx1 nCoV-19.
CanSino Biologics Inc
Developed by Chinese company CanSino Biologics and Beijing Institute of Biotechnology, the vaccine reportedly showed promising results in phase 2 testing
Moderna/NIAID (Phase 3 not yet recruiting)
Moderna of US is developing a vaccine using messenger RNA (mRNA) to enable the body to produce viral proteins itself.
Bharat Biotech, Phase 1 & 2
Being developed by Hyderabad-based Bharat Biotech and National Institute of Virology, the human clinical trials of India’s first indigenous vaccine Covaxin is on.
Russia announced that it has developed “world’s first coronavirus vaccine” and claimed that the vaccine has been tested and was “safe”. Prime Minister Mikhail Mishustin has claimed that his country would produce a “reliable vaccine” by “the fall”.
University of Queensland
Researchers are developing a vaccine by growing viral proteins in cell cultures. It is in phase I trial.
Clinical trials in humans are classified into three phases: phase I, phase II and phase III.
In Phase I clinical studies, initial testing of a vaccine is carried out in small numbers (eg 20) of healthy adults, to test the properties of a vaccine, tolerability, and, if appropriate, clinical laboratory and pharmacological parameters. Studies are primarily concerned with safety.
Phase II studies involve larger numbers of subjects and are intended to obtain preliminary information about a vaccine’s ability to produce its desired effect in the target population and general safety.
Phase III clinical trial is for the pivotal study on which licensing is based and sufficient data have to be obtained to demonstrate that a new product is safe and effective. By the beginning of phase III stage of development, a vaccine should have been fully characterised and the final manufacturing process, specifications and batch release testing procedures should have been established.
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