Dr. Shyam P Lohani

Equitable distribution of the vaccines is the key to defeating the COVID-19 pandemic. In many western countries, vaccine rollouts are rapid, and hence mask and physical distancing guidelines are easing. And people are going back to their work and school. Many low- and middle-income countries are still struggling to get vaccines from the manufacturers and a large majority of people have not yet received even a first jab.
When the coronavirus that causes COVID-19 first started to spread, virtually everyone was susceptible to the virus. Without resistance, the virus spread quickly across communities, countries and reached almost everywhere in the world. The second wave in some countries and subsequent waves in others met with some resistance owing mainly to natural immunity (people developed immunity after becoming infected) and vaccination. However, stopping it will require a significant percentage of people to be immune to the virus.

Herd immunity
Natural immunity or a vaccine that provides full protection against SARS-CoV-2 offers the best chance for a return to normalcy. After becoming immune, we will be able to go for our daily life, free from the worry of getting infected, as well as the need to social distance and wear masks. The threshold point in which most of a population is immune to an infectious disease provides indirect protection or population immunity or herd immunity or herd protection to those who are not immune to the disease.
The mass vaccination programme is based on the concept of herd immunity. When a sufficient proportion of a population is vaccinated, the disease transmission is disrupted by surrounding the infected person with vaccinated individuals. The infectivity of the microbe and the number of secondary infections that are transmitted by a single index case in a susceptible population are to be considered to know the percentage of the population needs to get vaccines for herd immunity.
For example, if 50 per cent of a population is immune to a virus, half of the population who encounter someone with the disease will not get sick and spread the disease any further. This is the ultimate goal and how the spread of infectious diseases can be kept under control. Usually, 50-90 per cent of a population should have developed immunity before infection rates start to decline. However, the actual percentage of people developing immunity depends on how contagious the infection is.
Scientists initially assumed the percentage would be around 60 per cent to 70 per cent of people being vaccinated to achieve herd immunity that will provide safety even to those who are not vaccinated. The assumption was based on the fact that if around 66 per cent were immune because they had either recovered from the disease or had a vaccination, the reproduction number (R) would fall below one. At such a point, one infected person would then infect less than one other, and the pandemic would dwindle as a result.
Scientists now believe that around 80 per cent of people would have to be vaccinated for the pandemic to be brought to an end because the novel coronavirus is more infectious than was initially thought. Now, the new variants of coronavirus such as UK, South Africa, Brazil, and India are also causing uncertainty about herd immunity as they spread 30-70 per cent faster than the original virus. Another concern is about the effectiveness of available vaccines against variants.
There have been reports of a decrease in transmission of the virus from vaccinated people; however, it is not yet clear to what extent vaccination reduces transmissibility. The available data, so far, suggests vaccinated people are between 67-94 per cent less likely to transmit the virus.
In countries like Nepal where the population of 0-18 years old is about 40 per cent, it is not possible to reach herd immunity with vaccination of the adult-only population. The reason behind this is that the World Health Organisation (WHO) currently does not recommend vaccination to young children, pregnant women, and people who are allergic to vaccines. Also, the currently available vaccine’s efficacy is between 67-95 per cent, there is still the remaining percentage in whom they will not have the same effect. However, it is good news that the composition of younger populations in many low-income countries has led to lower COVID-19 mortality.

Prevention
Although it is important to get vaccinated in protecting ourselves from COVID-19, it does not mean we can stop taking precautions such as wearing masks, social distancing, and hand hygiene. Those preventive public health measures are still critical as we continue to battle the pandemic. At present, a large number of active cases are present; getting the vaccines does not mean we can go back to life as before. Therefore, it is important to continue to take all the recommended precautions, so we can protect ourselves and others. Until we really get a decrease in the active COVID-19 cases, all of that remains crucial to contain the spread of the disease.
A transition to normalcy depends on how rapidly we receive vaccine supply, how our vaccination campaign runs, and the impact of vaccination on hospitalisation rates and mortality, and the resurgence of cases due to new variants. Health professionals believe that the virus is unlikely to be eradicated as it has spread all over the world and it will keep coming back. In a slightly hopeful scenario, let us hope that the virus will become endemic and behave like a seasonal flu.

(Prof. Lohani is the founder and academic director at Nobel College. lohanis@gmail.com)