Dr Musa Mohd Nordin, Paediatrician
Asst Prof Mohammad Farhan Rusli, Public Health Physician
19 August 2021
The whole idea of ramping the vaccination rates is to achieve herd immunity, whereby a large enough critical mass in the country is immune thereby conferring indirect protection to the unimmunized cohort of the population.
Herd immunity is a function of the Reproductive Number, RO.
Herd Immunity (HI) = 1-(1/RO)
If the RO of the virus is accepted at the low of 6.0 (ranges between 6.0 – 8.0), then the herd immunity would be equal to 1 – (1/6) = 0.83
83% of the population needs to be immunized in order to achieve population immunity. [1]
With 16% of those surveyed refusing to be immunized and another 17% unsure about the COVID-19 vaccines, it is highly unlikely that herd immunity will be achieved and protection of the population is not feasible with vaccination alone.
It would seem that the pandemic waves of COVID-19 would only dwindle or cease when virtually everyone has achieved immunity either through vaccination or infection with the virus.
Then the SARS-CoV-2 becomes an endemic coronavirus like it’s 4 other predecessors that causes the common cold.
89% of the more than 100 experts surveyed by the magazine Nature, responded that SARS-CoV-2 was either very likely or likely to become an endemic virus. [1]
Herd immunity also requires the candidate vaccine to be effective against all forms of COVID-19 infection, asymptomatic and symptomatic, not just the more severe forms.
From the outset the vaccines were designed to prevent the severe manifestations of COVID-19, namely hospitalizations, ICU admissions and deaths.
This it has done very well, even in the face of the more transmissible and virulent Delta variant. In fact, it has surpassed the vaccine efficacy of the bi-annual influenza vaccination which pivots at about 60%.
We will therefore need a high efficacy vaccine to achieve the herd immunity of 80%. Challenged by the Delta variant the VE of the various vaccine are as illustrated in the table:
The waning immunity with time of all the available vaccines especially the inactivated vaccines would mandate a booster dose. This unlike the live attenuated measles and varicella vaccines which has a VE of 97% and 98% respectively with 2 doses and has conferred virtually livelong immunity.
To begin with, the inactivated vaccines produced less protective neutralizing antibodies when compared with the mRNA vaccines. [3]
Studies have also shown that the neutralizing antibodies further declined 6 moths after the second dose. Only 35.2% of the vacinees had neutralizing antibodies above the “minimal protective level”. A third booster dose has been shown to increase the levels by 3-5 folds. [4]
Israel has immunized their high-risk groups, the senior citizens and the immunosuppressed and it is beginning to show dividends.
Thailand’s preliminary data has shown that 2 doses of Sinovac boosted by a third dose of the AstraZenca vaccine produce significantly higher neutralizing antibody titres. [5]
Malaysia needs to seriously consider this option as emphasized in the earlier article. [6] Only with a formidable herd immunity, can we begin to see endemicity kicking in.
Malaysia must start its booster dose planning now, as this requires detailed planning for the mix and match of vaccines, procurement of the effective booster doses in order to effectively exit the pandemic safely. This is to ensure that we do not miss the early boat just like we lapsed during the first round of vaccination.
It is high time that we begin to analyze the responses of our vaccine beneficiaries at the level of their protective neutralizing antibodies. This needs to be incorporated as a scientific parcel in our National Testing Strategy, just like the Thais have vindicated their boosting with the AZ vaccine. We need to do better, learn from our mistakes and endeavor to never return to crippling lockdowns and economic collapse.
Meanwhile, the pandemic trinity of masking, distancing and hygiene in tandem with ventilation needs to be in place for a bit longer to buy some time to suppress the transmission of the virus and protect the capacity of our healthcare services, and build reserve surge capacity for any upcoming waves.
Smart and savvy risk communication of this transitioning to endemic COVID-19 is of paramount importance. In the past, the authorities have miserably failed with the basics of informing, educating and inspiring the rakyat.
Until and unless this strategic communication failure is addressed promptly and professionally, one of the reset agenda of regaining the trust of the rakyat will falter miserably.
References:
- https://www.publish.csiro.au/ma/pdf/MA21009
- https://www.nature.com/articles/d41586-021-00396-2
- https://www.nature.com/articles/s41591-021-01377-8
- https://www.medrxiv.org/content/10.1101/2021.07.23.21261026v1
- https://m.facebook.com/thiravat.h/posts/4662726457094205
- https://drmusanordin.com/2021/08/18/the-covid-19-endgame-the-now-what-next-and-the-future-part-i/
