COVID-19 HERD IMMUNITY

 

Herd immunity is the indirect protection from a contagious infectious disease that happens when a population is immune either through vaccination or immunity developed through a previous infection.

This means that even people who are not vaccinated, or in whom the vaccine cannot be administered, are protected because people around them who are immune are deemed to act as buffers between them and an infected person.

Once herd immunity has been 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 eradicated smallpox.

The more infectious a disease, the greater the population immunity is needed to ensure herd immunity. For example, measles is highly contagious and one person with measles can infect up to 18 other people. This means that around 95% of people need to be immune in order for the wider group to have herd immunity.

The new coronavirus strains have a slightly lower infection rate than measles. This means that herd immunity should be achieved when between 70% to 80% of the population becomes immune to Covid-19.

However, natural herd immunity - achieved through infection rather than vaccination – can be challenging to induce through unchecked infection as there would be a very high rate of serious illness and death, with the healthcare system overwhelmed well beyond their surge capacity, even in high-income countries. This is why herd immunity is generally pursued through the vaccination programmes.

Even when vaccines are available, it is not always possible to achieve herd immunity within a short period of time. Some viruses, such as the seasonal flu, mutate frequently, evading the body’s immune response. So, immunity does not always last forever, which is why the flu shot is necessary every year.

Mass vaccination will mean that the Covid-19 virus will start to dissipate on its own but we may find ourselves months down the road still battling the threat, and having to deal with future surges.

Scientists point to several other factors such as vaccine hesitancy,

vaccine availability, the continued mutation of the virus causing new variants, and delayed vaccination approval for children as the main causes for the inability to reach herd immunity.  

Mass vaccination has been highly successful in inducing herd immunity for many diseases, protecting those that are unable to build up immunity, such as people with immune deficiencies or whose immune systems are being suppressed for medical reasons. 

When herd immunity is well established, some people may choose to behave as ‘free riders’, essentially benefitting from everyone else getting vaccinated, while abstaining from vaccination either because they choose not to or are actively anti-vaccination. When a population has too many of these free riders, the overall immunity level is compromised and herd immunity can be lost, putting everyone at risk.

The Malaysian Government has ordered enough vaccines for 109 per cent of the population who are eligible for vaccination. This was done after calculating the number of people above 18 years old and those suitable to receive the vaccination. If we can get the vaccines delivered on time, then we could achieve herd immunity before the end of this year. 

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