Page 3 -

Let's Talk about the 'V' word: EXPERT OPINION

Vaccination

Viruses, especially RNA viruses, are notorious for their ability to undergo mutation during their replication cycle. This led to the
emergence of new variants, as can be seen in SARS-CoV-2. The novel virus has been able to spread worldwide as a result of evolution
and adaptive mechanisms. First, the D614G variant replaced the original strain. Then, the B.1.1.7 Alpha variant, followed by the B.1.351
Beta variant, the P.1 Gamma variant, and now the B.1.617.2 Delta variant have been found. These variants share one advantage of
having a higher transmission rate due to the mutations on the virus' spike protein, allowing it to bind efficiently to the ACE2 receptor.
Unfortunately, this means more binding, higher viral load in the respiratory tract, more chances of spreading, therefore more cases and
hospitalisation.
So, we need to develop a better intervention plan to delay the To put it simply, to calculate the percentage of individuals to be
introduction and further spread of a new variant of concern through vaccinated to achieve herd immunity is 1 – 1/R0. The higher the
a robust vaccination program. The current vaccines presently being R0, the higher the herd immunity threshold. Say, for R0 of 4
distributed worldwide are mRNA, viral vector, and inactivated (Delta variant’s reproductive number is thought to be double
vaccines. The vaccines all have one purpose; to prime the body by that of the original); we need to vaccinate about 75% of the
directing the immune system to produce antibodies against specific population to gain immunity to stop the transmission. However,
pathogens, so the body develops immunity without getting the this is a rough figure as scientists can only estimate the herd-
disease. Without this immunity, infectious diseases from novel immunity threshold due to the complexity of the basic
pathogens will spread like wildfire. reproduction number, but that is a whole other story.
Nevertheless, the questions on everyone's mind are, will the Still, the actual numbers would not be known until after
vaccines work against the multiple variants of SARS-CoV-2 circulating analysing the data in retrospect, years to come.
in different parts of the world? Moreover, will we ever achieve the
hypothetical herd immunity threshold and began transitioning back Waning immunity
to our everyday life? Meanwhile, vaccine manufacturers have already developed

'Breakthrough' infections booster doses to improve efficacy and the waning of immunity
against circulating variants. It is worth mentioning that antibodies
As no vaccine is 100% effective, those who are vaccinated could still are not the sole driver of immune protection. Other vaccine-
be infected. This is a cause for concern for many of us when there induced immune cells, such as T and B cells, also play a role in
are reports of 'breakthrough' COVID-19 infections in countries with a immune defence, but it is still unclear how they respond when
high rate of vaccinations. So, what is a breakthrough infection? A challenged by the Delta variant. Thus, the conversation about
breakthrough infection occurs when someone tests positive for whether booster doses are needed yet is ongoing. While the
COVID after being fully vaccinated, regardless of symptoms. more infectious Delta variety continues to spread, diminishing
However, most breakthrough infections cause minimal or no immunity will result in additional outbreaks. We may need to re-
symptoms, indicating that vaccines effectively protect us from severe vaccinate people to maintain herd immunity once we know how
disease and death. Yet, it is essential to remember that vaccines are long the protection lasts. In addition, we may anticipate
not meant to protect us from infection, so there will be more vulnerable populations like the elderly and those with weak
breakthrough cases as more people are vaccinated. In addition, immune systems to be the first to be exposed to illness as
people who have had a breakthrough infection can still infect others. immunity declines.
Furthermore, early research suggests that people who have been
immunised can have high virus levels in their nasal cavities, possibly Where to from here
as high as people who have not been vaccinated. Nevertheless, this Managing this as we transition to living with COVID will be a long-
is not a cause for alarm as being vaccinated and immunised allow us term challenge for all countries. Lockdowns are not to be
to clear the virus more rapidly, minimising the time we are implemented frequently or for long periods; however, it is
contagious and spreading the infection. difficult to predict the future because so much depends on the
competence of the public health personnel to test, trace, isolate,
ViAs reported by CDC, our current COVID-19 vaccines are highly
effective against hospitalisation and death for variants including and quarantine. A return to a normal timeline in each country
Alpha, Beta, Gamma and Delta. However, available data also suggest depends on so many factors such as daily case counts, vaccine
lower effectiveness against confirmed infection and symptomatic distribution speed, and vaccine uptake by the population, which
disease caused by the Beta, Gamma, and Delta variants than the essentially relies on the public's willingness. What would be
ancestral strain and Alpha variant. The drop in effectiveness should alarming is to observe a significant rise in completely vaccinated
not cause panic, for all the vaccines are still doing well against Delta. individuals becoming severely ill and dying — but that is not the
However, ongoing monitoring of vaccine effectiveness against case. Therefore, as we work our way to get the vaccines to the
variants is still needed. arms of all the targeted populations in Malaysia, we still need to
rely on non-pharmaceutical intervention approaches to live our
With that being said, vaccinated individuals are less likely to be a lives.
source of infection and protect those who cannot be immunised by
limiting the spread of the disease. This concept is called herd Dr Jasmine E. Khairat
Senior Lecturer
immunity. Herd immunity thresholds (the proportion of the Institute of Biological Sciences
population that must be vaccinated and immune) differ depending Faculty of Science
on how contagious a disease is. PAGE 1
Universiti Malaya