Endemic has become a fairly fashionable word recently. But we are not sure if we share similar ideas and understanding of this epidemiological concept.
The health minister, like most of his colleagues in the 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 per cent of the population has been fully immunised.
The concept of population immunity has been well addressed by Dr Amar-Singh 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 Ministry of Health (MOH) is on the same page.
Like Dr Amar, I think the minister needs to again confer with his advisors to see whether 80 per cent 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 (Ro) of 2.5, the population immunity, in the presence of a Vaccine Efficacy (VE) of 90 per cent, 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 per cent of the community needs to be vaccinated before we might consider moving towards the endemic phase.
It is in this context that the MOH must ramp up the vaccination of our 12 to 17-year-olds in order to achieve the 90 per cent population immunity. Children below 18 comprises 29 per cent of the total population at 9.3 million. With 16 per cent 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 refugees, asylum seekers and undocumented migrants.
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 cases, hospitalisations, ICU admissions, brought-in-dead (BID) cases and hospitals deaths will be “tolerable” and manageable, not overwhelming our health care 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:
- 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 develop severe adverse effects to the vaccines.
- Individuals who refuse the vaccines for themselves or their families.
However, we have to contend with breakthrough infections in the fully vaccinated, but these are mainly Categories One and Two 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.
Various strategies have been advocated to tackle this, which includes:
- Longer spacing between the vaccine doses.
- Booster doses for high-risk geriatrics, the immunosuppressed, and the frontliners who are past six months after their second dose.
- A mix-and-match strategy which have been shown to produce better immune responses.
- The utilisation of more immunogenic vaccines which have been shown to hype higher titres of neutralising antibodies, B and T memory cells, and which last longer in the system., which might even obviate the immediate need for a booster dose.
And while we improve our vaccination strategies, we need to simultaneously improve other public health strategies which are equally important to reduce cases, decrease associated morbidities, mitigate BID numbers, hospital mortalities, ensure our health care facilities has adequate surge capacity reserves, and ensure our frontliners are not burnt out with this long-running war against the coronavirus.
Dr Musa Mohd Nordin is a paediatrician and Asst Prof Mohammad Farhan Rusli is a public health physician.
- This is the personal opinion of the writer or publication and does not necessarily represent the views of CodeBlue.
