The Covid-19 pandemic that started from China, with the first case being reported in December 2019, has entered the new era with the start of Covid vaccination drive at the end of 2020 globally and 2021 in India. As the herd immunity against the virus is increasing, by vaccination or the natural infection, we see that the virus is also showing mutations to overcome the antibody pressure. As such, the new strain from the United Kingdom and other countries has shown a second wave of increasing Covid infected patients. In India, some states like Maharashtra, Kerala are currently the worst affected states with a huge number of active cases. Other states in the country are also showing rising trends of new cases of Covid- 19 infection. A good way to control the spread of the disease is by intensifying the vaccination drive. As we see, now the vaccine is also being given to high-risk population i.e. 45 years and above with co-morbidity and 60 years above with the availability of both Covishield and Covaxin for vaccination at both government and private aided centres. This has increased the ease of getting the vaccine as per individual convenience. It is also important to note that the selection pressure is always there among the infective microorganisms, leading to the genomic mutations in them for survival in adverse conditions, as a part of the immune-escape phenomenon. Many countries like the United Kingdom, Brazil, etc have witnessed the second wave of the pandemic mostly due to mutated strain. We can say Darwin’s theory of “Survival of the fittest” hold true for the viruses also.

As such, it is also to be checked time and again related to the effectiveness of the current vaccine. The current vaccines that are approved by DCGI in India, are Covishield and Covaxin. Covishield is a viral vectored vaccine, which means it is a part of the Covid genome that is overlapped in an animal virus that enters the human cells and provides immunity against those antigens. Covaxin is an inactivated virus of Covid-19 that acts as the antigen as a whole. The latest clinical trial data of Covaxin has shown 81% efficacy in the Indian population after the second dose of vaccine with no major side effects.

The vaccination drive started in January and as the clinical trial data suggest, the antibody response is noted only after two weeks of the second dose of vaccine that is taken four weeks apart. The herd immunity from vaccination to protect the susceptible population first, that are more vulnerable to acquire the infection or to develop the severe disease, will start showing effect only after a considerable number of population is vaccinated after a defined period. Also, it is recommended that as antibodies developed after natural infection may last for one to three months depending upon the initial immune response, the person who had recovered from Covid infection should also take this vaccine.

As the country moves forward with this huge vaccination programme and more and more people get the vaccine, we can have the desired herd immunity (around 70% of the population with the protective antibodies), and successfully halt the ongoing pandemic.

The writer is Consultant – Infectious Diseases, Manipal Hospitals, New Delhi.

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