Vaccines create immunity without causing complications. Using the concept of herd immunity, vaccines have earlier successfully controlled deadly contagious diseases. Despite attaining herd immunity through vaccination has its own drawbacks, however, writes RAJENDRA T NANAVARE, herd immunity makes it possible to protect a population from infectious diseases.

The CoViD-19 pandemic is perhaps the greatest healthcare challenge of a generation. India’s coronavirus epidemic is growing the fastest in the world, having increased alarmingly over the last few weeks. Timely diagnosis and treatment give patients the best chance to recover. We have come a long way since then and the knowledge and experience gained over this time has certainly helped to better manage the afflicted.

A second infection follows recovery from a previous infection by the same causative agent. The first three confirmed reinfections in the world were reported in the first week of September this year – one in Hong Kong and two in Europe, all mild.

According to a study, people who tested positive after discharge from hospitals only had leftover viral debris in their bodies, and not live virus – a distinction RT-PCR tests failed to make.


It has been ten months now since CoViD-19 was first detected in December last year in Wuhan, China. One set of worries addressed, another arose when a Chinese study suggested in June this year that antibodies against the novel coronavirus start fading within two to three months.

In the early days of the pandemic, it wasn’t understood whether the antibodies generated by the body against the novel coronavirus were long-lasting. Reports of re-infections in South Korea triggered fears that those who had recovered from the infection could contract it again. But a study conducted by the South Korean government confirmed in May that this was not true. Cases of CoViD-19 reinfection from Hong Kong and Europe put the world’s worst fears to test – what would happen if a person catches CoViD-19 more than once within a short duration.

India’s first confirmed CoVid-19 reinfection cases were reported from Greater Noida hospital in two nursing staffs by using whole genome sequence and, later in Mumbai, four health care workers (HCW) in which three were doctors from BMC Nair hospital and one HCW from Hinduja hospital were confirmed by using whole genome sequencing. It was found the first time CoViD-19 was mild but on reinfection the severity was on the higher side.


The immune response to any kind of pathogen is in incremental steps or layers. Immune system cells are primarily made up of leukocytes or white blood cells, which circulate through our body and scan for suspicious objects. As soon as we are infected, the first kind of immune system – the “innate” kind – kicks in. It is non-specific, so it protects against all pathogens the same way. The innate immune response triggers the adaptive immune response, which is more specific to the kind of pathogen infecting our bodies. The adaptive immune response consists of T cells and B cells. B cells are the ones that produce antibodies or immunoglobulins to fight off the infection and help recovery.

T cells and B cells also produce memory cells that are capable of storing information about antigens. These cells, called memory T cells and memory B cells, take a few days to trigger after the first instance of infection, but invoke a swift and efficient response the next time the pathogen is encountered.


Herd immunity is a form of indirect protection from infectious diseases which occurs when a sufficient percentage of a population has become immune to an infection, whether through vaccination or previous infections, thereby reducing the likelihood of infection for individuals who lack immunity. Immuned individuals are unlikely to contribute to disease transmission, disrupting chains of infection, which stops or slows the spread of the disease.


A vaccine is a biological preparation that provides active acquired immunity to a particular infectious disease. Vaccines can be prophylactic or therapeutic. Vaccines are important because a lot of resources are saved in preventing a disease and not having to treat it. Vaccines have been key to the elimination of once dreaded diseases such as smallpox.

There are two paths to achieve herd immunity in case of CoViD-19 — (i) vaccines and (ii) infection. Herd immunity through natural infection. There will be a very high number of cases and deaths – hundreds and thousands – overwhelming hospitals and bringing the healthcare system to its knees.

A vaccine for the virus that causes CoViD-19 would be an ideal approach to achieving herd immunity. Vaccines create immunity without causing illness or resulting complications. Herd immunity makes it possible to protect the population from a disease, including those who can’t be vaccinated, such as those who have compromised immune systems.

Using the concept of herd immunity, vaccines have successfully controlled deadly contagious diseases such as smallpox, polio, diphtheria, rubella and many others. Reaching herd immunity through vaccination sometimes has drawbacks, though. Protection from some vaccines can wane over time, requiring revaccination. Sometimes people don’t get all of the shots that they need to be completely protected from a disease.

RAJENDRA T NANAVARE is Chest physician & Chairperson DRTB center, Bedaquilin at GTB hospital, Mumbai, Ex-Pharmcovigilance in Drug Safety Monitoring committee for Bedaquilin at I.C.M.R and Ex-Consultant for international union against tuberculosis and lung diseases. He is also postgraduate teacher for Chest & TB in College of Physicians and Surgeons, Mumbai. He can be reached at

Opinions expressed in this article are of the author’s and do not represent the policy of The Edition. The writers are solely responsible for any claim arising out of the contents of their articles.

Tags: #Covid19 #Coronavirus #HerdImmunity #Vaccine #Leucocyte #TCells #BCells #Immunoglobulims