Immunology of flu pandemic

Print and electronic media is overflowing with a lot of stuff on present outbreak of Coronavirus pandemic – COVID-19 that has forced closure of academia, business and industry worldwide-rather a social curfew in view of its threatening public emergency.

COVID questions, answers, speculations, preventions and challenges find a prominent coverage in newspapers and magazines. Medical scientists are working day and night to find the most effective treatments and possible vaccine to curb this menace.

However, at the same time it is equally important to aware the common people about the working of our immune system to tackle flu or influenza infections to which COVID-19 belong.

The material presented in this article is not intended to be comprehensive but is only a glimpse of immunological aspects of human flu and I hope it will provide a useful soothe for interested readers in these fearful and apprehensive moments.

To begin with, let me assure you that the best preventive measure and treatment to get rid of flu and influenza like symptoms in our body is adequate rest, sleep and healthy diet.

The reason being, less or lack of sleep makes us more prone to catching flu because inflammatory cytokines of our immune system increase under such physiological conditions driven by less sleep and our T- immune cells go down if we are sleep deprived.

So remember, adequate sleep and proper diet keeps the components of our immune systems always primed for attack to infectious agents and subsequent protection.

Basically flu viruses are small segments of genetic material in the form of RNA with a binding protein coat (which is spiky in coronaviruses) requiring always host cell machinery for their survival and multiplication.

The flu or influenza infections in human populations stop of their own after a specific period of time – thanks to the working of our immune system with a series of coordinated events for an effective flu protection.

Had it not been the case, every type of flu whether seasonal, routine or zoonotic will prove a catastrophe to human survival, because once a flu infection occurs in an individual or groups of individuals it spreads like a fire in a population due to a variety of direct and indirect contacts.

And depending on the severity, an infection may prove fatal for life but not alone due to the particular flu attack but due to already immuno-compromised status of some people due to various secondary/opportunistic infections or some debilitating diseases or people who are on immuno-suppressive drugs.

The best thing is that the surviving infected populations automatically become immune due to prior illness or infection that drives the development of herd immunity (the proportion of subjects with immunity in a given population or community).

In this way a particular virus finds it harder to find a new susceptible human being in population/s or groups of populations. So herd immunity or community immunity means presence of enough immune people (50-70%) in a population of a region with a natural capability of stopping the spread of infection.

Staying indoors or social lockdown is therefore, unfavourable situation for the working of our immune system against COVID-19, it will rather hamper the process of development of herd immunity against it, more the people are exposed to its infections, and greater are its chances of natural clearance from the populations.

Despite potential of herd immunity, prevention and protection of new-borns, pregnant, diseased and older people assume highest significance in minimising the flu attack to them, because they are immunologically week or deficient to tackle flu infections.

Generally, our immune system works against viral attacks in a variety of specific and non-specific ways, for example, blocking the binding of virus to host cells, neutralisation by antibodies (but only in acute infection phase), enhance their phagocytosis, generate certain direct antiviral molecules like interferon’s, activation of natural killer cells, killing of virus infected cells by cytotoxicity, etc.

Overall, cell mediated immunity in the form of specialised CD8+ and CD4+ cells is more important for viral control and clearance (once the infection is established- the latent phase).

However, flu viruses evade these host defense mechanisms by a variety of means ranging from immuno-evasion, immuno-suppression, antigenic drift (small genetic change) and antigenic shift (abrupt and major genetic change resulting in new types, for example as happens when certain animal viruses infect human – zoonotic infections) to escape the already developed immunity in the human populations and emerge as new or novel strains as has happened with the present Coronavirus originally present in its reservoir host-the bats.

Once it shifted to human in new avatar (strain), it could easily get transmitted to other human irrespective of any barrier.

The actual evolutionary reason behind this antigenic variation of flu viruses is to avoid the cross immunity or cross protection (immunity against one type of flu virus will act against antigenically similar viruses) of human populations. That means every time new or novel flu infection happens, our immune system has to start from zero to achieve immunity against the novel strains.

This is the reason that worst COVID-19 pandemic is going on presently without a protective immunity in human and non-availability of pre-available vaccine/s or antiviral drug/s.

Believing nature, a selective group of people or populations may have to perish due to pandemic flu obeying the principle of natural selection- the guiding and controlling principle for a species.

However, an individual with a high immunological fitness will provide more beneficial contributions in controlling the spread of this infection in the population. We can say such an individual curtails the freedom of virus to choose and infect fresh population.

This principle enables us to understand how a human population may evolve by determining which individuals are contributing beneficial and immunologically tolerant or resistant genes (capable of developing herd immunity) to the next generation.

Because in the struggle for survival on this planet, individuals with particular genotypes and phenotypes or traits will be more successful than others in terms of their response to infections and diseases.

The writer teaches Zoology at the Islamia College, Srinagar.