First-off-the-block COVID-19 vaccines – Expert Briefing

The Science Media Centre led an online briefing about promising COVID-19 vaccine candidates, including the mRNA vaccine from Pfizer and the adenovirus vaccine from Oxford/AstraZeneca.

Associate Professor Helen Petousis-Harris, University of Auckland

The full briefing is available here and an abridged transcript is below.

How does an mRNA vaccine work?

“Basically, the vaccine itself actually contains the instructions for our own bodies to actually make the vaccine. So, rather than… having the thing that provokes the immune response inside the vial, if you like, this has got the instructions for it. And in this case, and it’s also the case with the viral vector vaccines as well, that our bodies’ own cell machinery actually translates this instruction into the vaccine antigen and then what we might like to call an ‘antibody-generating’ protein – the thing we want to make the immune response against.

“And then from there, the immune system really takes over and responds by making immunity against this. I guess that’s how very fundamentally it works: it actually gets you to make the vaccine yourself.”

Is there any risk of an mRNA vaccine affecting human DNA?

“No, because your DNA – your instructions to make you – is contained within the cell, it’s contained in the cell nucleus. This mRNA has no way to actually access this part of the cell. I mean, that’s one reason: it can’t actually access it.

“And the other reason is that if it were to be able to get in there, and actually integrate or do something to our genome, it would need to be something like a retrovirus or something like that, which it’s not.

“So, there’s actually no biologically plausible way that an RNA vaccine can meddle with your genome. It’s likely to be very, very safe.”

If these mRNA vaccines are successful, will we see scientists trying the mRNA technique out with other diseases existing now?

“Absolutely. They’d already been developing vaccines against some of the more neglected diseases and had been making some progress, and there were some other coronavirus vaccines that had actually been tested in humans, not as far as these ones now. But, there had been some progress, and they really were looking like a way where we could perhaps develop vaccines very quickly and more cheaply.

“I think now we’ve seen the power of this technology unleashed, so I don’t think you’ll be putting it back in the box anytime soon. I think it opens up more options for other diseases.”

There have been news reports of two NHS workers over in the UK having allergic reactions in response to the Pfizer COVID-19 vaccine. The NHS is now telling people with severe allergies to stay away. Is this kind of reaction normal for such a new vaccine?

“First of all, I don’t think we really know exactly what sort of reaction or event that these people have had. I’ve seen the media reports and they’re a little inconsistent. But also, some of the descriptions suggest that they’re… I don’t think very clear on exactly what’s happened. So, perhaps they have had some kind of allergic response. Exactly what sort? I don’t think we know. I’m sure that data is being examined right now. It’s really, really important to let the investigation run its course, rather than trying to kind of guess what might have happened.

“We also need to be really clear that we’re going to see lots of events happen after people have been vaccinated, because everyday, in any population, lots and lots of health events are happening all the time. When we start vaccinating lots and lots of people, we are going to see events happen, and there are very, very good systems in place to assess these and come to some sort of conclusion as to what the role of the vaccine might be and whether there’s an increased risk. So, we kind of have to let those play out. We’re going to see this happen a lot so we need to figure out… how we discuss this because it is challenging when we hear these alarming stories. We have to sit back, take a breath, and let the investigations happen. I think that’s really important.”

Is this type of reaction something you’ve heard of happening with any other vaccine before?

“I think probably most, not all perhaps, but most vaccines all come with a very, very small risk of anaphylaxis, which is the life-threatening allergic reaction. A life-threatening allergic reaction will occur very quickly after injection, so that’s why people are asked to stay for about 20 minutes afterwards because that’s something that the vaccinators are trained to treat immediately.

“It’s very rare, in the order of about on average one per million, so that’s really rare. Most vaccinators have never seen this happen.

“What can happen is a lot of misdiagnoses of these. In fact, we’ve had examples of mass immunisation campaigns in New Zealand where a whole lot of people on one day appeared to have these anaphylactic reactions. It turned out – and there was a pretty sharp paediatrician actually on the scene quite quickly – they were actually faints. They weren’t anaphylaxis. That, you can imagine, it almost blew up into a huge media story with all these people having these terrible events. So, we have to be very careful because there’s a very specific diagnosis for this type of event, for anaphylaxis, and it does need to go through the proper evaluation, so we just need to be careful.”

Might this news put some people off getting the vaccine and what can be done to limit that if so?

“Yeah, I think any story about adverse events after a vaccine can, of course, increase people’s hesitancy. I think we have to reassure people, and get to grips with the idea that we are going to see events happen after vaccines. It’s inevitable. We have really good systems in place – we just saw the system in the UK kick in when it happened yesterday… and let that run its course. For example, the regulator – the people responsible for overseeing the safety – will be able to tell us what conclusions they come to, and we’re going to have to leave it with the people who got all the details of these cases. I mean, I don’t even know how long after the vaccine that these people had these events, for example, which is a very important piece of information.”

Would you have any message to worried people in New Zealand specifically as these vaccines get nearer to New Zealand?

“I think once we start vaccinating, we’re actually going to have data on tens of millions – if not hundreds of millions – of people [as it’s] already rolling out in the UK en masse and the US will be behind, and other countries soon to follow. So, by the time we actually start using it, we’ll have the benefit of quite a lot of new information and a lot of data.”