Difficulties in achieving herd immunity

 Difficulties in achieving herd immunity

After a public remark made by the national Covid-19 immunisation programme co-ordinating minister Khairy Jamaluddin, in which he said that he no longer thinks herd immunity can be achieved and he has stopped using the term, this drives some members of the opposition and public into a frenzy.

Some questioned Khairy if this is so, does it imply that the current vaccination programme is a waste of time and resources?

Conveniently or carelessly, they also ignored the important fact and message that Khairy is still very much pushing for more people to get vaccinated, regardless of the scientific fact that it is not practical to achieve herd immunity.

The term, also known as population immunity, is an indirect form of protection from an infectious disease for to those who are not immune, when a sufficient percentage of a population is immune either through vaccination or exposure to previous infections.

The World Health Organization (WHO) advocates vaccination restricting the spread of disease that would result in unnecessary cases and deaths.

Our government sets the target at 80% vaccination coverage of the population, and aims to achieve this by the end of this year.

This leaves many in the public to believe that herd immunity is just a number target, once we achieve that number then it means we have achieved herd immunity.

This is probably one of the most prevalent public perceptions but factually incorrect and misleading.

There are many factors to explain why herd immunity for Covid-19 is evidently difficult to achieve, even with high percentage coverage of the vaccinated population.

First, the greatest benefits of the current vaccines in our portfolio are the protection from severe illnesses and death due to Covid-19, and this could significantly relieve the burden on the public healthcare system.

While the efficacy of the vaccines preventing the infection varies depending on a person’s risk community profile and the local infection force, it is well documented that the vaccines we have currently are not silver bullets.

There were incidents where even people vaccinated were becoming infected with the added possibility of passing on the virus.

However, compared to unvaccinated people, vaccination can still reduce and slow down, but not eliminate Covid-19 transmission.

Second, people often overlook the distribution of the vaccinated population. High coverage of them would be useful for herd immunity protection only if the distribution is even.

That means it is no use of having more than 90% of the urban population vaccinated, while some rural villages and certain urban community pockets (such as migrant hidden communities) are left totally unprotected.

The latter communities will serve as the potential reservoir or outbreak point for virus transmission.

Third, even if it is just a number target, to reach 80% population coverage is an enormous challenge.

To date, no one country has achieved that level. The leading country Israel has plateaued at close to 60% vaccinated population since April.

For Malaysia, the challenge to get to this number is partly due to the fact that 30% of the population is under 18 years old.

Even after the government announced that 12-17 years old residents can be vaccinated with the Pfizer/BioNTech vaccine, that only addressed about 12% of the entire population (and they still need parental consent).

At the end of last year, the Health Ministry conducted a large-scale survey, which gathered 212,000 respondents, and the results finding shows that 17% were unsure and 16% did not agree with vaccination.

Thus realistically, since the immunisation programme is voluntary, the government has to persuade about 30% of the adult population to change their mind.

Given the currently “untouchable” under-12 population already consists about 17%, the margin of error is in fact very small for the government’s failure to convince the remaining reluctant population.

The factors beyond the control of the government are the global inequity of vaccine distribution and the possibility of emergence of new variants of virus, which are more threatening than the currently known variants of concern (VOC).

Mutation is considered a relatively rare event for SARS-CoV-2 virus which has a length of about 30,000 bases and it contains a certain proofreading mechanism when the virus is copying its own genome sequence.

The majority of mutations would have no effect or even be harmful to the virus itself.

However, it is a different scenario when we continue to allow more infection cases to go around the world.

As long as there are areas or countries in the world that cannot effectively control the disease outbreak, there will be patients suffering prolonged disease infection.

These patients could potentially be the incubator for the new variants of virus, as they would allow more rounds of viral replications, hence more likely for the virus to make “mistakes” and create mutation.

The variant with more advantageous mutations in terms of higher binding affinity to the human cell receptor, more efficient replication mechanism and evasion of immune response, can be selected and passed on to the community, and finally could become the dominant circulating variant, such as the Delta variant affecting the 47% vaccinated UK population.

Border control measures could block the import cases containing these new virus variants, but it could only effectively work to a certain extent. Currently, three out of four VOC listed by the WHO –Alpha, Beta and Delta – have already hit our shores.

How could we have the confidence to prevent the new emergence of VOC or even variants of high consequence (VOHC) from coming in, in near future?

The VOC and VOHC will keep on challenging and weakening the effectiveness of the current vaccines.

Some scientific evidence from studies already pointing at reduced effectiveness of neutralising antibodies from the current vaccine response.

The good news is that the current vaccines administered in Malaysia are still good enough to protect us from hospitalisation and death, other aspects of vaccine-induced immune response such as T-cell-mediated immunity are largely intact and effective.

Make no mistake, vaccines are still an important tool for disease control measures in our country. Vaccination rollout should be one of the core exit strategies but cannot be the only game in town.

If the vaccine supply is available, it is imperative to get many people vaccinated as soon as possible.

At the same time, public health measures, whether medical or non-medical interventions, are still crucial at controlling disease transmission.

The government has to address the issues of public trust deficit by vastly improving the risk communication and putting up coherent and reasonable policy measures, while the public (including employers and business owners) has the responsibility in complying with standard operating procedures.

We need a whole-of-society approach, not “holes-in-society” contributing to the spike of disease cases and spread.

59th article for Agora@TMI column, published on The Malaysian Insight, 28 Jun 2021