Herd immunity: What you need to know

Herd immunity happens when enough section of the population has built up immunity to a disease, making the transmission of the diseases less probable.

As a result, the whole community is protected from the disease, not just the one who are immune.

Herd immunity only applies to contagious disease that is transmitted from one individual to another. Tetanus, for example, is an infectious disease contracted from the environment, hence herd immunity will not work.

A “herd immunity threshold” which is the minimum percentage of immune individuals needed to establish herd immunity, must be achieved to stop the spread of a disease.

For example, it is estimated that 93-95 per cent of the population must be immune to measles to build herd immunity for the diseases and stop the chain of transmission.

There are two ways in which herd immunity can be achieved:

When a number of people have had the disease and recovered from it, they are likely to have developed antibodies against future infection.

This would allow for herd immunity to develop in the community as more people are considered immune to the virus.

Vaccination is a much more reliable and faster way to achieve herd immunity and makes it possible for those who can’t get vaccinated such as newborns and those with compromised immune system, to receive protection as well.

Vaccine has been proven effective in controlling many deadly infectious diseases such as smallpox, rubella, polio and many others.

The main obstacle in developing herd immunity for COVID-19 is that the virus is new and there hasn’t been enough data on COVID-19 immunity for experts to work on to build herd immunity.

The absence of vaccine as the most effective way to build herd immunity also makes it hard for any progress in the subject.

With no vaccine, a large number of people would need to catch the virus, get sick and either recover or suffered detrimental side effects and possibly die, before we can have herd immunity.

This in turn would also lead to healthcare systems being overburdened when many people develop COVID-19 at the same time.

The World Health Organization (WHO) is also unsure whether the presence of antibodies in blood gives full protection against reinfection of the virus.

Mike Ryan, WHO ’s top emergencies expert, said that even if antibodies were effective, there was little sign that large numbers of people had developed them and were beginning to offer herd immunity to the broader population.

“A lot of preliminary information coming to us right now would suggest quite a low percentage of population have seroconverted (to produce antibodies),” he said.

Health Director General Tan Sri Dr Noor Hisham Abdullah said that Malaysia “prevention and control” method has been proven to be better at handling the COVID-19 pandemic than developing herd immunity.

Acknowledging that the herd immunity concept has been recommended by many public health experts, he believed that Malaysia’s approach thus far has been successful.

“We didn’t know who was right then, but the last 10 months showed that the countries that used the same approach as us managed to contain their cases better, compared to those who embraced herd immunity,” said Dr Noor Hisham at the ministry’s COVID-19 press briefing yesterday.

While herd immunity would mean that more people will get antibodies to fight the virus, Dr Noor Hisham said that the approach would put vulnerable communities such as the elderly more at risk.

He added that many nations are impressed by Malaysia’s handling of the pandemic and are even using the country as a benchmark.