UNDERSTANDING HERD IMMUNITY

 by: Pharmacy Services KPJ Penang Specialist Hospital -  Farah Jasni

Is herd immunity alone enough?

A recent survey was done by the Health Ministry regarding Malaysians’ acceptance of the Covid-19 vaccine shows that 67 per cent of the 212,006 respondents are willing to take the Covid-19 vaccine. This is a good indicator in building up a herd immunity system in our battle against Covid-19 pandemic. 

However, there is a group of people who are against the use of Covid-19 vaccines and continue to debate whether the safety, efficacy and stability of the vaccine are credible enough to be given to all Malaysians. The debate is further heated following the viral statement made by the former Pfizer's vice president, Dr Yeadon who claimed that Covid-19 vaccines were unnecessary as people globally were acquiring natural herd immunity by getting infected in large groups. WHO has then clarified that the view is unethical and false. Sacrificing more people by letting them get infected to acquire herd immunity naturally would cause more impact on the healthcare system and the country.

"Herd immunity is achieved when a certain population is immune to the virus thus making the virus outbreak stop expanding exponentially."

This has led to the big question of this article. What is herd immunity? 

When a part of the population is immune to an infectious disease, this will stop the spreading of the disease thus end the pandemic. This is called herd immunity.  When a large number of people in the population is vaccinated and immunized to the virus or bacteria, the spreading becomes difficult as there are only a few people left uninfected. By having herd immunity, the vaccinated population is also able to protect people who are unable to be vaccinated, such as newborns, people who are very ill such as immunocompromised and chemotherapy patients.

Examples of successful herd immunity are for diseases such as measles, polio and smallpox. These diseases are rare now, thanks to herd immunity established by using vaccines. It requires approximately 80% and above of the population vaccinated to achieve herd immunity, thus reducing the threshold of the disease contagiousness. The threshold of infectious disease contagiousness is represented by using the value that we often see in daily Ministry of Health (MOH) Covid-19 progress report, which is R0 or R-naught. The figure of R0 quantifies the average transmissibility of a disease. For example, if the R0 is 1, it means each case of Covid-19 will lead to another 1 new case.

Therefore, what is the target of R0 to achieve the optimal herd immunity in the attempt of winning the battle against this faceless war? 

Based on the press conference of Covid-19 on January 4, 2021, Tan Sri Dr Noor Hisham Abdullah stated that the Ministry of Health (MOH) target is to bring down the R-naught to 0.5 and it has not been achieved yet. Whereas on 9th March, the current R-naught is 0.86 and is expected to trend to 0.8 if the pandemic is controlled well. However, creating a strategy based on targeting R-naught only is not sufficient. Quoting physician and virology expert, Muge Cevik, the risk of transmission is complex and multi-dimensional. It depends on various factors such as how does the environment affect the pandemic, the contact pattern of the cases, the host factors of cases and socio-economic factors, which are explained on her Twitter thread regarding the dynamics of Covid-19 transmission. So, does having a target R-naught help in winning this battle? The answer is yes. Having a low R-naught helps to lower the risk of transmission of this virus thus optimal treatment can be given to the infected.

"The Risk of transmission is complex and multidimensional" - MUGE CEVIK

How does having Covid-19 vaccine help in herd immunity?

Through the national Covid-19 vaccination program where the population is vaccinated for free, most of the people will have then acquired good antibody to fight Covid-19 effectively. 

This leaves only a small portion of the population unprotected, thus reduces the R-naught and helps to build strong herd immunity.    While one might argue that herd immunity can also be achieved through the natural process by letting more people be infected, the current situation shows that this pandemic is already on the verge of breaking a country, damaging the economy worldwide and destroying every effort from the healthcare system in salvaging the situation. To quote WHO, attempting herd immunity by exposing people to strong viruses are scientifically problematic and unethical. When having a vaccination program across the country where a substantial proportion of a population is vaccinated, the R-naught is able to be reduced, the virus spread is lowered thus making us a step closer in winning the fight against the pandemic.

"Attempting herd immunity by exposing people to virus are scientifically problematic and unethical. "

What can we do before herd immunity against Covid-19 is achieved? 

Every one of us must ensure adherence to the health advisories and recommendations provided by the MOH. Always avoid the 3Cs - avoid Crowded places, Confined spaces and Close conversations.

Practice the 3Ws - Wash hands frequently by using water and soap; Wear face masks when in public areas and when having symptoms; and Warn self and others to avoid shaking hands or touching others, practice good sneezing and coughing etiquette, seek early treatment if symptomatic, stay at home and avoid from visiting others and regularly clean and disinfect commonly touched surfaces in common areas. By adhering to these health advisories, we may gain an early momentum of combating the virus.

Reference:

        1.            World Health Organization. (2020). Coronavirus disease (COVID-19): Herd immunity, lockdowns and COVID-19. Retrieved January 20, 2021, from 31 Dec 2020 website: https://www.who.int/news-room/q-a-detail/herd-immunity-lockdowns-and-covid-19#:~:text=The percentage of people who,immunity is not known.

        2.            CodeBlue. (2020, December). Khairy Corrects Ku Li’s Misinformation About Covid Vaccines. Codeblue.Galencentre.Org, p. 1. Retrieved from https://codeblue.galencentre.org/2020/12/09/khairy-corrects-ku-lis-misinformation-about-covid-vaccines/

        3.            Chung, C. (2021). Experts: Majority ready to accept Covid-19 vaccine but more awareness needed. The Star, p. 2. Retrieved from https://www.thestar.com.my/news/nation/2021/01/08/experts-majority-ready-to-accept-covid-19-vaccine-but-more-awareness-needed

        4.            Cevik, M. (2020). How SARS-CoV-2 Spreads, A thread. Retrieved from Twitter website: https://twitter.com/mugecevik/status/1308080058389729280?ref_src=twsrc%5Etfw%7Ctwcamp%5Etweetembed%7Ctwterm%5E1308080058389729280%7Ctwgr%5E%7Ctwcon%5Es1_&ref_url=https%3A%2F%2Fwww.vox.com%2F21451282%2Fherd-immunity-explained-covid-19-pandemic

        5.            Ministry of Health Malaysia, 2021. COVID-19 Malaysia Updates. [online] COVID-19 Malaysia. Available at: <http://covid-19.moh.gov.my/semasa-kkm/2021/01/unjuran-r-naught-12092020-hingga-31052021> [Accessed 12 February 2021].

        6.            Rashvinjeet S. Bedi. (2020, December). Covid-19: Natural herd immunity means a lot will get sick, says Khairy. The Star. Retrieved from https://www.thestar.com.my/news/nation/2020/12/09/covid-19-natural-herd-immunity-means-a-lot-will-get-sick-says-khairy

        7.            Resnick, B. (2020, October). What people get wrong about herd immunity, explained by epidemiologists. Vox.Com. Retrieved from https://www.vox.com/21451282/herd-immunity-explained-covid-19-pandemic

        8.            Zimlich, R. (2020, April). What Is Herd Immunity? Verywellhealth.Com. Retrieved from https://www.verywellhealth.com/what-is-herd-immunity-4801526

        9.            Hill, D. G. (2020, July). From the Frontlines: Understanding Herd Immunity. American Lung Association. Retrieved from https://www.lung.org/blog/understanding-covid-herd-immunity