COVID-19 VAX
As the COVID-19 vaccine rollout continues across Australia and New Zealand and the fearmongering of certain groups grows louder, we look at the science behind the Pfizer and AstraZeneca vaccines and debunk some common misconceptions.
It’s time to examine the science behind the vaccines and debunk some myths.
Since February, immunisation against COVID-19 has become possible thanks to government approvals for two COVID-19 vaccines. While these vaccines are new, their delivery methods (known scientifically as ‘platforms’) had been in development “before we even knew what COVID was,” explains the Malaghan Institute of Medical Research’s Dr Fran Priddy, clinical director of Vaccine Alliance Aotearoa New Zealand – Ohu Kaupare Huaketo (VAANZ).
Dr Priddy explains that new technologies have enabled scientists to create more advanced and complex platforms like those used by Pfizer and AstraZeneca. Whereas older style vaccines involved injecting a whole (or part of) a live or killed virus or bacteria, neither of the new vaccines take this approach. Rather, they use the tiny, knob-like surface structures you see on drawings of the coronavirus (called ‘spike proteins’), albeit in different ways.
The AstraZeneca vaccine uses what scientists call an ‘adenoviral vector’ platform, says Dr Priddy. This platform works by taking a type of virus called an adenovirus (in this case one that affects chimpanzees), modifying it so it can’t replicate and cause disease, and including the genetic sequence of the virus of interest – in this case, the SARS CoV-2 spike protein. The adenoviral vector infects some of your cells, delivers the spike protein sequence, and the cell then manufactures the protein and displays it on its surface. In effect, these cells are camouflaged to look like the coronavirus to trigger an immune response.
Pfizer’s vaccine uses what is known as an mRNA platform. Dr Priddy explains that this works by taking the genetic sequence for the spike protein and putting it into a protective fatty bubble, which is injected into your muscle. The mRNA then uses your own cells’ machinery to make actual spike proteins for as long as it lasts in your system, which is usually a few days. This mimics the situation of being exposed to COVID-19 for several days, “so your immune system gets a good look at the virus and is able to make a decent immune response,” she says.
DEBUNKING VACCINE MYTHS
Understanding a bit more about mRNA vaccines also helps dispel some of the misinformation you might hear about them. For example, there have been suggestions these vaccines could alter your body’s DNA code. However, this is impossible, Dr Priddy explains, because RNA cannot cross the barrier into the cell’s nucleus where your DNA resides. And even if the RNA could get across, “it couldn’t actually change your DNA anyway,” she emphasises.
Dr Daryl Cheng, paediatrician and medical lead for the Melbourne Vaccine Education Centre, confirms the Pfizer vaccine doesn’t hijack your body to alter its DNA or cause it to do something it’s not already doing. “Our cells produce huge amounts of RNA already so that’s a normal process,” he explains. “Other viruses that invade your body, such as influenza viruses, also invade cells and present RNA for replication.”
Another common concern is about the speed with which these vaccines were developed and approved, but people need not be worried. As Dr Priddy points out, the pandemic created a unique global focus that saw unprecedented levels of political will and funding targeted at vaccine research and development.
When a vaccine or other therapeutic agent is given rapid approval for use under urgent circumstances (known as an ‘emergency use authorisation’), the usual rigorous processes still apply. “Safety steps weren’t skipped,” Dr Priddy confirms. “This could be done so quickly because many of the steps that usually go in sequence were just done at the same time.”
As Dr Cheng elaborates, “In Australia, we started setting up to manufacture the AstraZeneca vaccine even before it was finally approved by the TGA. That meant we could start shipping the vaccine the same day approval was given.”
He adds that Australia and New Zealand were in the fortunate position of being able to wait for data from studies and vaccine rollouts from the US and UK, before making decisions around our own vaccine safety and rollout plans. “And that’s real-life data, not just test-tube data,” he says.
Furthermore, that data was based on solid numbers. Says Dr Priddy: “The number of people that received the vaccines during the clinical trials was as high as, if not higher than, numbers that have received vaccines that have previously been approved.”
For people concerned about the new technologies, Dr Cheng points out several vaccine platforms are already being used in Australia and overseas. With the flu vaccine, for example, a ‘boosted’ platform known as an adjuvanted vaccine is used for Australians aged over 65 to boost the immune response, which tends to taper off in that age group. “No-one really questions that. You just turn up and get your shot and carry on.”
EFFICACY VS EFFECTIVENESS
It’s also crucial not to confuse vaccine efficacy with vaccine effectiveness, Dr Cheng cautions. He explains ‘efficacy’
is a term used by researchers to describe the performance of a vaccine in reaching predefined goals in a controlled clinical trial. Efficacy does not measure how well the vaccine stops people from getting the disease in the real world. Rather, in COVID-19 vaccine trials, it measures how well it prevents people during the trial from getting symptomatic COVID-19 and, in particular, severe COVID-19. A 94 per cent efficacy, for example, means the vaccine prevented 94 per cent of infected people from dying or developing severe symptoms requiring hospital admission.
In contrast, effectiveness is the term used to describe how well a vaccine works in everyday life among the general population, which is much more accurate in terms of determining how ‘good’ a vaccine is. Because the vaccine rollout has only recently commenced, effectiveness rates are not yet available in Australia, although there are preliminary data from other countries.
COMPARING VACCINES
Importantly, though, confusion over the terms has created a misconception that one vaccine is ‘better’ than the other. “Pfizer was the first to report and said that their efficacy was above the 95 per cent mark. This was significant news because it was much higher than expected,” says Dr Cheng. “Then, AstraZeneca’s came out and, because of some challenges with the trial, they reported outcomes anywhere between 62 and 90 per cent. People looked at the numbers and immediately inferred it was an inferior vaccine.
“This has led to people saying Pfizer is superior to AstraZeneca and that people who get one brand are going to be more protected against the COVID virus. That is untrue; vaccine efficacy cannot be inferred to mean vaccine effectiveness.”
This isn’t to say vaccine efficacy doesn’t matter, because it relates to the public burden of the disease. As Dr Cheng says, “If I can keep 95-100 per cent of COVID-positive patients out of hospital, as per specific vaccine efficacy rates in the Pfizer and AstraZeneca trials, that is a significant win for both the healthcare system and the economy.”
Australia’s vaccine rollout was overhauled in April after an extremely rare clotting disorder was linked to the AstraZeneca vaccine. A handful of Australians developed thrombosis with thrombocytopenia (TTS) after receiving the AstraZeneca shot. The Federal Government consequently stated that the Pfizer vaccine is now preferred to the AstraZeneca vaccine for adults aged under 50 years.
IT’S NOT ALL ABOUT YOU
Another important reason those who can get vaccinated should do so is to protect others. The ‘holy grail’ of vaccines is being able to stop the spread of a virus. “And because there may be some people who are not able to get the vaccine, they have to rely on others in the community getting vaccinated to try and prevent transmission,” Dr Cheng says.
He explains that for anyone who belongs to a “special risk group”, vaccination may need to be discussed with their healthcare provider. This includes pregnant women or anyone planning a pregnancy, and people with weakened immune systems, such as those undergoing chemotherapy treatments or who take immunesuppressing agents for autoimmune or rheumatological conditions.
For the immunosuppressed, the advice is that it’s safe to get vaccinated. As Dr Priddy explains, the vaccines don’t contain a live virus, “so it’s very unlikely they will cause any harm. The question is, ‘Will they be as effective in immune-compromised people?’ We just don’t know that. Some immune-compromised people may choose to wait until there’s more data, and some may decide it’s worth getting vaccinated.”
Dr Cheng points out that problems can arise when people who’ve had the vaccine subsequently have treatments such as immunesuppressing medications or chemotherapy, because “these treatments may wipe their immunity and they’d need to have the vaccine again.” Alternatively, people may choose to time treatments that suppress immunity with receiving the vaccine. “Those decisions should be discussed directly with their health professional,” he says.
For women who are pregnant or planning a pregnancy, Dr Cheng says the current recommendation from the Australian Technical Advisory Group on Immunisation is that immunisation should be considered on a case-by-case basis.
“There are not enough data at the moment in regard to potential side effects or impacts on the mother or baby, so the risk to benefit ratio needs to be weighed up,” he explains.
Looking at the risk to benefit ratio applies to all immunisations, Dr Cheng adds.
With COVID-19, it’s important to consider potential risks of the vaccine versus the potential for getting severe disease from COVID, especially in special risk groups.
He emphasises that COVID-19 can cause much more than a cough or cold. “We’re starting to see that some people develop what we call longCOVID effects, where they survive COVID-19 disease but experience significant long-term complications and repercussions. You also need to weigh up the potential for spreading the disease to your loved ones.”
Decisions should take your personal circumstances into account. “If you’re a pregnant hotel quarantine worker, for example, that’s very different to being a pregnant woman who is working from home.
“For many of these discussions, we have to be honest and say we don’t have all the information because this is a vaccine that’s only been employed for four or five months. But all the evidence so far lands on the side that immunisation can significantly alter outcomes in a positive way. That, in and of itself, is a good reason to continue to use it as we gather data.
“Some people are hesitant because this almost seems like building a bridge as you cross it.
“But in the overall scheme of things, especially in places where the burden of disease is severe, it’s of significant benefit all the way from an individual level to the top, where governments have to manage the health and economy of the country and make sure healthcare systems are not overwhelmed.”
For up-to-date information about COVID-19 vaccines in Australia, visit health.gov.au/initiatives-and-programs/ covid-19-vaccines
“THE VACCINE CANNOT HIJACK YOUR BODY TO ALTER ITS DNA.”