Following the publications of the efficacy trials of the mRNA vaccines and viral vector based vaccines, there has been a plethora of data examining whether these vaccines actually work when used in the real world. (Click here, here, here, here, and here). This article attempts to summarise some of the vaccine effectiveness data.
Clinical trials have shown that all the “authorised” Covid-19 vaccines showed good vaccine efficacy (VE ranged from 65-95 per cent) against symptomatic, laboratory confirmed SARS-CoV-2 infections. They demonstrated high VE (>89 per cent) against hospitalisations and were 100 per cent protective against Covid-19 associated deaths.
Preliminary data also suggest that the vaccines may also prevent the transmission of the virus.
In the Moderna trial, the number of asymptomatic subjects who tested positive for SARS-Cov-2 was two-thirds lower in the vaccine group than the placebo group.
Johnson & Johnson’s interim analysis suggested a 74 per cent reduction in asymptomatic infection.
The US Centers for Disease Control and Prevention showed that in real-world conditions, the first dose of Pfizer or Moderna vaccines was 80 per cent in preventing infections in health care workers, other frontliners and essential workers. After the second dose, the vaccine effectiveness was 90 per cent.
Following the vaccine rollout in the US to the general adult population, the administration of two doses of either the Pfizer or Moderna vaccines showed a VE of 89 per cent. Both sets of real0world vaccine effectiveness data are close to the VE of 95 per cent and 94 per cent of the Pfizer and Moderna vaccines in the clinical trials.
In the UK, the Pfizer VE was 86 per cent and 89 per cent in health care workers and adults more than 80 years old respectively.
In Israel’s national mass vaccination campaign, researchers compared 596,618 vacinees with matched unvaccinated controls. Two doses of the Pfizer vaccine was 94 per cent effective against symptomatic Covid-19 infections and 87 per cent against hospitalisations.
The Pfizer vaccine also reduced the transmission of the coronavirus. It showed a significant 80 per cent (0 days after the second dose) and 94 per cent (14 days after the second dose) reduction of asymptomatic Covid-19 infection in the US and Israel respectively.
The severity and transmissibility of Covid-19 disease is closely related to the viral load. This study from Spain demonstrated the viral load of index cases was a key driver of SARS-CoV-2 transmission. The probability of developing symptomatic Covid-19 disease was strongly correlated with the viral load of the index cases.
Early research from Israel’s vaccine rollout programme demonstrated that persons vaccinated with one dose of the Pfizer vaccine had viral loads 1.6 to 20 times lower than in unvaccinated, infected persons.
This study report that the viral load fell by 2.8-4.5 in people who received one dose of the Pfizer vaccine and then developed a breakthrough Covid-19 infection.
The population study following the mass vaccine rollout in Israel also showed that the Pfizer vaccine is effective against the B.1.1.7 variant (UK), because during the study period, this variant made up 80 per cent of the circulating SARS-CoV-2 isolates in Israel.
When a sufficient proportion of the population has been immunised against Covid-19, herd immunity is achieved. The spread of the coronavirus ceases, and even those who have not been immunised for various medical or philosophical reasons are protected. This threshold for Covid-19 infection is at least 65 per cent.
Israel is leading the world in this respect and has fully immunised 58 per cent of its population. A further 830,000 (9.2 per cent) Israelis have been naturally infected with the SARS-CoV-2 virus. So, approximately 67.2 per cent of Israelis can be considered as having protective Covid-19 antibodies which is very close to the threshold of herd immunity.
There has been a 95 to 97 per cent reduction in confirmed Covid-19 cases in all age groups in Israel. It remains to be seen whether the cases in Israel continue to remain suppressed at the current low levels.
Israel has now lifted its yearlong policy of mandatory masking in public spaces. And all of its primary and secondary schools have been reopened.
At the height of the Covid-19 pandemic in the early part of 2021, Israel had the world highest cases per capita. With its rapid speed and aggressive scale-up of the vaccine coverage, it has now set the precedent as to how to control and contain the coronavirus.
Unless Malaysia has adequate access to authorised vaccines — like Israel that had sufficient access to Pfizer’s vaccine — Malaysia needs to seriously consider hastening the conditional registration of the other mRNA vaccine, Moderna, which has been shown to be very efficacious in clinical trials and has been proven in the real world experience.
In fact, the vaccine portfolio should also be extended to the other Covid-19 vaccines, namely the Sputnik V and the Johnson and Johnson vaccines which has been shown to be efficacious in clinical trials and has been published in peer-reviewed medical journals.
This is unlike the inactivated Covid-19 vaccines which lack published interim data analysis and, therefore, poses difficulty in attempting to verify and validate their claims on vaccine efficacy and safety.
Amendment on April 24: The last paragraph and third-last paragraph were amended to reflect the writer’s original intention after inadvertent edits.
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