Can Herd Immunity be an effective way to tackle COVID-19?
Herd immunity is the risk of infection among susceptible individuals in
a population that can be reduced by the presence and proximity of immune
individuals, referred to as “herd effect” or “indirect protection”
(Fine, Eames, & Heymann, 2011). It is actually a strategy of indirect
protection from an infectious disease that occurs when a population is
immune either through immunity developed from previous infection or
vaccination. This means that even people who are not vaccinated, or
people in whom the vaccine doesn’t trigger immunity, are protected
because people around them who are immune can act as buffers between
them and an infected person (Randolph & Barreiro, 2020).
Once herd immunity is established for a while, and the ability of the
disease to spread is hindered, the disease can eventually be eliminated,
this is how the world wipe out smallpox (Bazin & Jenner, 2000). The
more infectious a disease, the greater the population immunity needed to
ensure herd immunity. For example, measles is highly contagious and one
person with measles can infect up to 18 other people. It means that
about 95% of people are needed to be immune in order for the wider
group to have herd immunity (Dowdy & D’Souza, 2020).
While this novel coronavirus has a lower infection rate than measles,
with each infected person passing it on to two or three new people, on
average. This means that herd immunity can be achieved when around 60%
of the population will become immune to COVID-19, this strategy can be
economical and beneficial for developing countries like Pakistan who
can’t afford to vaccinate their whole population due to limited
resources and current ongoing financial crisis. However this can only be
achieved when a vaccine will develop for COVID-19. (Kwok, Lai, Wei,
Wong, & Tang, 2020).
Another type/ way of herd immunity, natural herd immunity, that is
achieved through infection rather than vaccination. It means that if a
large number of population is infected with certain infectious strain,
antibodies against that infectious agent will naturally be formed in the
body that will protect them from reinfection. It can be challenging to
induce it through unchecked infection as there would be a very high rate
of serious illness and death. Health systems will be overwhelmed well
beyond their surge capacity, even in high-income countries (Bethune &
Korinek, 2020). That is why herd immunity is generally pursued through
vaccination programs, even when vaccines are available, it is not always
possible to achieve herd immunity for very long duration. Some viruses,
such as seasonal flu, mutate frequently and evade body’s immune
response. So, immunity does not always last forever due to which flu
shot is necessary every single year. Similarly, in the case of
coronavirus, natural immunity to the virus may also last only a year or
two (Wu et al., 2007).