Dr Musa Mohd Nordin, Paediatrician
Asst Prof Mohammad Farhan Rusli, Public Health Physician
Endemic has become a fairly fashionable word recently. But we are not sure if we share similar ideas and understanding of this epidemiological concept. [1]
The Health Minister, like most of his colleagues in cabinet have dumped most if not all of their eggs in the vaccine basket. He predicts that by the end of October, the nation will move into the endemic phase when 80% of the population has been fully immunized. [2]
The concept of population immunity has been well addressed by Dr. Amar, when he wrote, “it is important that we stop talking about or showing data on adult vaccination rates and concentrate only on total population vaccination rates” to ensure that the MOH is on the same page. [3]
Like Amar, I think the Minister needs to again confer with his advisors whether 80% coverage is a safe enough indicator for a friendly co-existence with the raging Delta Variant Of Concern (VOC).
It would be possible if it was the virgin Wuhan or even the Kent Alpha VOC. With the Wuhan coronavirus Reproduction Number of 2.5, the population immunity, in the presence of a Vaccine Efficacy (VE) of 90%, would be achieved with:
[ (Ro-1) / Ro ] / VE = [ 1.5/2.5 ] / 90% = 67%
However, the Delta VOC has been demonstrated to be more transmissible with an Ro of 5-7. Even using the conservative Ro of 5.0, at least 88% of the community needs to be vaccinated before we might consider moving towards the endemic phase. [4]
It is in this context that the MOH must ramp up the vaccination of our 12-17 year olds in order to achieve the 90% population immunity. Children below 18 comprises 29% of the total population, 9.3 million. With 16% of the adult population against the COVID-19 vaccines, it is a tough call to achieve this vaccination target.
And we have not even begun to calibrate the other potential epicentres of COVID-19 clusters, namely the refugees, asylum seekers and undocumented migrant populations.
Vaccination will only help to checkmate transmission and fizzle out an outbreak, if this level of community protection is achieved. With less spread of the virus, the incidence of COVID-19 cases, hospitalizations, ICU admissions, brought in dead (BID) and hospitals deaths will be “tolerable” and manageable, not overwhelming our healthcare services and allow us to “live with the virus”.
The concept of herd immunity still holds because the vaccinated population will confer indirect protection to the other vulnerable non-vaccinated segment, namely: [5]
- Children under 12 years old who are not yet eligible for the vaccines
- Those who are allergic to the contents of the available vaccines
- Those who developed severe adverse effects to the vaccines
- Individuals who refuse the vaccines for themselves or their families.
We however have to contend with breakthrough infections of the fully vaccinated, but these are mainly Category 1 and 2 COVID-19 infections with the rollout of the mRNA and adenovirus vector vaccines. There is not as much data on the inactivated vaccines in the face of the Delta VOC threat. [6]
Various strategies have been advocated to tackle this, which includes:
- Longer spacing between the vaccine doses [7]
- Boosters doses for the high risk geriatrics, the immunosuppressed, and the front-liners who are past 6 months of the second dose [8]
- Mix and match strategy which have been shown to produce better immune responses [9]
- Utilization of more immunogenic COVID-19 vaccines which have been shown to hype higher titres of neutralizing antibodies, B and T memory cells, and which last longer in the system. Maybe even obviating the immediate need for a boosting dose [10]
And whilst we improve our vaccination strategies, we need to simultaneously power other public health strategies which are equally important to plunge the COVID-19 cases, decrease the associated morbidities, mitigate the brought in dead (BID) numbers, hospital mortalities and ensure our healthcare facilities has adequate surge capacity reserves and our front-liners are not burnt out with this chronic warfare against the coronavirus. TBC
REFERENCES:
- https://www.nature.com/articles/d41586-021-00396-2
- https://www.nst.com.my/news/nation/2021/09/723446/covid-19-endemic-stage-malaysia-expected-late-october
- https://www.malaysiakini.com/columns/590054
- https://www.businessinsider.com/delta-variant-herd-immunity-90-percent-2021-8
- https://drmusanordin.com/2021/06/22/herd-immunity/
- https://twitter.com/drmusanordin?lang=en
- https://theconversation.com/covid-19-extending-the-gap-between-vaccine-doses-was-the-right-thing-to-do-163293
- https://drmusanordin.com/2021/08/19/covid-19-endgame-2/
- https://drmusanordin.com/2021/07/17/targeted-vaccination-strategy-in-the-klang-valley-negeri-sembilan-and-labuan-to-overcome-the-variants-of-concern/
- https://www.ft.com/content/aaddc31b-415d-43d0-b314-bc89a8b860e0
