On July 26, 2021, Malaysia achieved a new record of 521,923 vaccines administered in a single day. This is optimistic news as it indicates the country is on track to achieve herd immunity and consequently protect the most vulnerable groups of the population against the Covid-19 virus.
Nevertheless, concerns and speculations are rife regarding the effectiveness of the vaccines against new and emerging strains of the virus, such as the Delta variant.
The Delta variant was first reported in December 2020 in India, and subsequently caused a second wave of infections across the country. A staggering 350,000 to 400,00 new cases were reported in a single day during the peak of the second wave.
Another notable country that is currently experiencing a surge of new infections due to the delta variant is the United Kingdom. On June 16, Public Health England reported that the Delta variant has surpassed the Alpha variant as the dominant strain in the country. The Delta variant now accounts for majority of the new infections in the UK, currently battling its third wave of infections.
Therefore, our concerns about vaccine effectiveness against this highly transmissible variant are justifiable. Nevertheless, there is limited peer-reviewed scientific evidence on current vaccine effectiveness against the Delta variant.
A study evaluating vaccine effectiveness against the Delta variant was published on 21 July by the New England Journal of Medicine. The study collated data pertaining an individual’s vaccination status, test results, and the specific strain of the virus identified.
The study included individuals from the age of 16 onwards. In total, 100,414 unvaccinated and 77,296 vaccinated individuals were included into study to investigate vaccine effectiveness in protecting against symptomatic disease caused by the Delta variant.
Before we look into the study’s findings, it is important to understanding the definition of vaccine effectiveness used in this study. This is because the definition of vaccine effectiveness can vary from one study to another.
Imagine a scenario where there are 15 unvaccinated people, and five of these people have tested positive for the virus. Subsequently, 11 vaccinated people were identified, and only one was tested positive.
The positive-to-negative ratio will be 0.50 (5: 10) and 0.10 (1:1 0) for the unvaccinated and vaccinated group, respectively. Given that the ratio in the vaccinated group is 20 per cent of the unvaccinated group, this translates into vaccine effectiveness of 80 per cent.
The study demonstrated that the Oxford-AstraZeneca vaccine is 30 per cent effective against the Delta variant 21 days after the first dose was administered. This number increased to 67 per cent 14 days after the second dose was administered.
Similarly, the Pfizer-BioNTech vaccine is 36 per cent effective against the Delta variant 21 days after the first dose was administered. This number increased to 88 per cent 14 days after the second dose was administered.
Taken together, it is reassuring the current vaccines are effective against the novel Delta variant, and this study’s findings can serve as an incentive for Malaysians to look forward to both doses of the vaccines.
Sean Wen is a DPhil student in medical sciences at the University of Oxford.
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