Vaccines that do not prevent or cure COVID still beneficial: Study

Anastasia Tsirtsakis

11/01/2021 3:58:41 PM

As Australia moves closer to its COVID vaccine rollout, experts discuss new US modelling that suggests reducing the virus’ contagious period could prevent millions of cases.

Deteriorating COVID virus
Australian experts have said the new modelling is based on assumptions that can only be confirmed as more people are vaccinated against COVID.

In the 12 months since the first confirmed case of SARS-CoV-2 in China, scientists around the world have done what usually takes several years, developing multiple viable vaccine candidates to fight the novel virus.
And just weeks after some of those candidates were approved for use, more than 25 million people in 42 countries have been vaccinated. 
While a major achievement, none of the vaccine candidates in circulation can entirely prevent the virus from entering the body, nor stop its transmission. But according to a new computational analysis, outright prevention or cure may not be the be all and end all.
The research, led by Bruce Lee, Professor of Health Policy and Management at City University of New York, suggests that a vaccine or viral treatment that can shorten the infectious period of COVID-19 by just half a day for 25% of confirmed cases could avert up to 1.4 million infections and more than 99,000 hospitalisations.
Cut the infectious period by 3.5 days for 25% of cases, and that number increases to 7.4 million. Expanding treatment to 75% of cases, including asymptomatic infections, could avert 29.7 million cases.
‘There may be a tendency to overlook vaccines and other treatments that don’t prevent a COVID-19 infection or cure disease,’ Professor Lee said. ‘But this study showed that even relatively small changes in how long people are contagious can significantly affect the transmission and spread of the virus.’
Epidemiologist Professor Raina MacIntyre, head of the Biosecurity Research Program at the Kirby Institute, says the modelling is ‘plausible’, but adds that vaccines, rather than antiviral treatments, are more likely to be effective in reducing transmission.
‘Vaccines are the only feasible way to do it because most of the infectiousness would occur prior to people knowing that they’re infected. By the time they get tested, they’ve probably already infected everyone that they’re going to infect,’ she told newsGP.
‘So if the vaccines don’t prevent infection – and they will prevent infection in some people, but the percentage of that will vary from vaccine to vaccine – all the vaccines do seem to reduce the severity of infection.
‘We don’t have the biological studies to prove that it reduces the duration of infectiousness, but it would make sense that it may do so.’
Former World Health Organization (WHO) epidemiologist Associate Professor Linda Selvey is a public health physician and infectious diseases epidemiologist at the University of Queensland.
She told newsGP the modelling is a ‘no brainer’ in that it confirms what is already understood about viral spread, but that it is based on assumptions that can only be confirmed as more people are vaccinated against COVID.
‘Intuitively you would think that the vaccine, even if it doesn’t prevent infection, will reduce the duration of infection because it’s based on your immunity and so on – but we don’t know that for sure,’ she said.
‘An example of what we do know is if we look at the polio vaccine. The live oral polio vaccine prevents transmission, as well as polio. Whereas injectable only doesn’t prevent transmission, but it does prevent people getting disease, and there certainly has been transmission of polio with people only immunised through the injectable form.
‘It does seem to reduce the amount of transmission that occurs, but it doesn’t get rid of it altogether.
‘But the [new] modelling is based on assumptions that at the moment we’re not in a position to test. I think that information will come out though fairly quickly from experiences in countries where they’re rolling out the vaccine and where there’s also a lot of transmission happening.
As long as they’ve got good surveillance, we will learn a lot over the next couple of months.’

Epidemiologist Professor Raina MacIntyre says vaccines, rather than antiviral treatments, are more likely to be effective in reducing COVID transmission.

According to Australia’s COVID-19 Vaccine Roadmap released last week, priority population groups, including GPs, are set to receive the Pfizer/BioNTech candidate, which has an efficacy rate of 95%. The majority of the population, however, will receive the University of Oxford/AstraZeneca candidate, which, based on current data, has an efficacy rate of 70%.
The modelling would suggest a lower efficacy rate could still have significant benefits in curbing the pandemic. But it may take longer to achieve the end goal of elimination, according to Professor MacIntyre.
‘[The AstraZeneca vaccine] will have a positive impact in the sense that it’ll protect people from dying or getting seriously ill needing intubation, etcetera. But it won’t be able to eliminate COVID,’ she said.
‘Whereas the higher efficacy vaccines may be able to eliminate it.’
The modelling also showed significant financial benefit for reducing the contagious period and, in turn, transmission.
A reduction of just half a day for 25% of symptomatic people could result in a saving of US$209.5 billion in direct medical and indirect costs. Increasing that to 3.5 days by treating 75% of symptomatic and asymptomatic cases had a projected saving of US$856 billion.
Associate Professor Selvey says the savings are more relevant to countries with high community transmission, like the US, and believes the individual cost of infection priced by researchers – US$500 – is likely set too low.
‘Those costs of individual cases are probably a bit of an underestimation given all the implications, not just for the case, but for all the quarantining of case contacts and the costs of that as well,’ she said.
‘But it’s not that relevant to our situation [in Australia] because we’re in a very fortunate position where we don’t have a lot of cases.’
The epidemiologist says what is most important is that once the rollout commences that it is ramped up as quickly as possible. She adds, however, that the modelling reinforces the need to continue putting other preventive efforts into action, which the Federal Government’s new vaccine education campaign will seek to emphasise.
‘Vaccinate as much of the population as is possible to vaccinate; that’s going to be the most effective way to protect people,’ Associate Professor Selvey said.
‘But we still will need to continue with good surveillance, testing, isolation and quarantine even with the vaccine, simply because no vaccine is 100% effective.
‘It is important that people understand that vaccination is absolutely important but also that it’s not a panacea.
‘We’re quite familiar with it in terms of the flu vaccine. Many of us get vaccinated even though we know it’s not 100% effective because it still does protect many of us from getting influenza. But there’s also a lot of people who don’t get the flu vaccine. So it’s a nuanced message.
‘So it is important that people get vaccinated, but also understand that that’s not the end of the story, unfortunately.’
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