Covid 19 coronavirus Delta outbreak: Vaccine expert Helen Petousis-Harris answers your questions about the Covid jabs

The Pfizer vaccine shows the way out of lockdown. Photo / George Novak

As New Zealand enters its third week of lockdown (though those south of Auckland can enjoy takeaways) vaccination offers the country a way back to the new normal. But some questions around the drug and the rollout remain. Auckland University Associate Professor Helen Petousis-Harris, a world-renowned expert on vaccines and vaccinations, answered subscribers' questions on all things Covid jab-related in a live online chat earlier today. Here's what she had to say.

Q: Do you think restrictions should be loosened for vaccinated people?
A: I think there is an argument for this but not until most people have had the opportunity to be vaccinated. Auckland hospitals are at capacity with their negative pressure rooms so we cannot manage more cases.

Q: Do you foresee needing jabs every year to boost immunity/deal with mutations, as with the annual flu?
A: I think we can expect boosters but suspect, as the infection becomes less in the populations, that it would not need to be annual. This coronavirus mutates much more slowly than the flu virus.

Q: Do you agree that vaccine certificates should be implemented? And if you are double jabbed and have a vaccine passport, would it be void after six months if you do not get a booster?
A: I think a vaccination record will be very helpful. While we have a pandemic raging there is an argument for proof of vaccine status for many public health reasons. I guess these are all questions we have to grapple with as the data comes to hand. As the public threat of Covid-19 eases, I imagine policies around vaccination proof will also evolve.

Q: What's the optimal lag between doses of the Pfizer jab?
A: Three weeks is the minimum space but the perfect space is not really known. There is no maximum - your body responds to the first dose and begins to develop a memory. We do know that a bigger gap - six-week, eight-week, 12, 14 weeks... - might be a little better but there is a lot of variability here. I think we can be relaxed about the spacing at the moment and the recommendations come down to pragmatism in getting the vaccine rolled out.

Q: Why does immunity wane following some vaccines but not others?
A: Briefly, all vaccines with the exception of polysaccharide vaccines induce immune memory. Sometimes this needs a boost to maintain protection. This is particularly relevant for very fast-moving infections such as meningococcal disease and Delta. This is because we need lots of antibodies ready to go in our blood and not dozing. Some vaccines are also better at doing all this than others.

Q: There's been a range of adverse effects resulting from the Covid vaccine reported internationally. The risk of dying from Covid-19 is low. Why should I be vaccinated?
A: The vaccines have completed very robust trials and 5.5 billion doses have been used in people. Safety has been monitored closely, particularly in the US and Europe with huge numbers [of people getting the jab]. No matter how young and healthy you, are your risk of becoming ill or dying from Covid is far, far greater than of you having a serious adverse event from the vaccine. The most serious event related to the mRNA vaccines is myocarditis, almost always mild in these cases. In all scenarios, it is much safer to have the vaccine than Covid. Also, we are seeing far more serious cases in young people with the Delta variant.

Q: How transmissible is the Delta variant in a partly vaccinated society?
A: Good question, and one that does not really have a good answer yet. There are a vast number of variables that go into the overall impact a vaccine has on the disease, the efficacy of the vaccine is only one... We do know that transmissibility of Delta is still reduced in vaccinated people but how this overall affects the incidence [how fast people catch the disease], we will need to wait and see.

Q: Why do people who've had both doses of a Covid vaccine still get infected?
A: Very few people who have been fully vaccinated are getting Covid-19, and even fewer are ending up in hospital. However, quite a few are getting infected without [getting] symptoms. This means [they] can pass it on... I would argue that the same people are generally not getting sick [who would have otherwise] and that when they are getting infected (as some do), they are transmitting [the virus] for a shorter period of time than the unvaccinated. This is possibly due to the combination of waning antibodies in the blood and the incredible speed that Delta moves. The reason they don't get sick and transmit for a shorter period might be because their immune memory kicks in and removes the virus before this happens.

Q: I'd like to get my child vaccinated, but they're aged under 12. Is this safe and possible?
A: The science almost supports it! The clinical trial results for this age group are due to be revealed this month and I understand authorisation in the US is likely to be October. Not sure about NZ but the intent is to test the vaccine down to six months old.

Q: If people have natural immunity from being infected with Covid, do they need a vaccine?
A: There is data to indicate that vaccine immunity might be superior; I imagine this depends on the vaccine type but for the Pfizer [jab], this looks good. People previously infected are recommended to get a dose. This [the vaccine] will be a pretty good boosting. There are limitations to testing people for immunity so we're not able to tell someone they have protective immunity by a blood test yet -only that they have had an immune response.

Q: Is it safe to be vaccinated against Covid while pregnant?
A: Pregnant women and their babies are at higher risk for Covid-19 complications (a bit like with flu). In the US, they were a priority group early on for the vaccine so there is now a lot of safety data. Two key reasons I would be confident about the safety in this group: 1. there are no biological reasons for a safety concern - the vaccine does not pass to the fetus; 2. the safety data in the pregnant [population] looks good.

Q: What's the deal with a vaccine rollout before clinical trials conclude at the end of 2023?
A: It's a common misunderstanding about when the trials "end". Trial endpoints for authorisation were completed last year (does it work and is it safe?). Studies continue for as long as is practical to collect additional data. For example, when might we need a booster? All vaccines are studied for the time they are in use, be it 10 years or 50 years; by that argument, they are all experimental. VAERS data is used to detect unexpected events, like an early warning system. Anyone can make a report. VAERS data cannot tell you if the event was caused by a vaccine. We use other methods for this.

Q: Can you convince me of the long-term safety of mRNA vaccines, such as the Pfizer jab, particularly among young people?
A: Vaccine adverse events occur within a short window after vaccination - two months max; most [are within] two weeks. This vaccine is no different.The vaccine components are degraded fast. The first people received mRNA vaccines many years ago now, and the first to receive a Covid mRNA vaccine are now about 18 months on. After hundreds of millions of doses, there is no indication of long-term [side] effects. There is an increased risk for myocarditis in males under 30 - usually mild and resolving quickly - around a 30 in a million risk. With the Covid [infection], a 450 per million risk and much more severe.

Q: How much would a Made in NZ Covid vaccine cost?
A: Starting from scratch, perhaps a couple of billion dollars. The biggest costs are with the Phase III clinical trials and a facility to manufacture. Not for the faint-hearted! However, we could possibly manufacture some types with a smaller investment.

Q: Could vaccines contribute to the evolution of vaccine-resistant variants?
A: Yes, it is likely this will happen, particularly in places that have vaccinated a lot of people but fall well short of targets – like getting half the population vaccinated, not most of them. This is another reason why high coverage is important. I suspect the next generation Covid vaccine will have a role to play when they become available. As the virus gets beaten back, these concerns will lessen.

Q: I understand that RNA use in vaccines was being researched several years before Covid hit. Can you confirm this and comment on the safety of this technology in relation to other vaccines?
A: Yes. MRNA vaccine have decades of history. The first in humans was for cancer vaccines, then infectious diseases from (i think) the 90s. MRNA vaccines are likely to be safer than most vaccines because the mRNA disappears in hours to days. So far this is bearing out to be the case. Serious events are extremely rare - as in, a few per million.

Q: What methods are available for researchers to gain assurance the risk of these long-term side effects is low? Do we have previous studies that show signs of long-term side effects from vaccines nearly always show up within the first year or two, especially when there's such a large population given the vaccine? Do you have different concerns for the different types of vaccines?
A: This is an impossible expectation and also very unlikely. First, there is no biologically plausible reason why a vaccine adverse effect might manifest a decade down the track. Second, this has never occurred in relation to another vaccine. Third, side effects occur within a couple of months tops and usually within two weeks. There is one exception to this and that is vaccine-mediated enhanced disease (VMED). The Covid vaccines have been thoroughly assessed for this potential; between preclinical, clinical and now real-world experience, this seems highly unlikely.

Q: Does the vaccine post a risk to fertility?
A: I think this idea comes from the misconception that the mRNA somehow interferes with our genomes. This is not true and biologically impossible. Also, the vaccine does not have access to our reproductive bits. The evidence would also argue against this as studies have shown outcomes of pregnancies/birth after receipt of Covid vaccines. In contrast, Covid can be particularly nasty in pregnancy and threatens both mother and infant. We have quite a bit of safety data now for pregnant women.

Q: Does having the vaccine reduces one's ability to develop an immune response to subsequent variants or possible other types of infections?
A: This is the first time I have heard this one! It would be the opposite. Each exposure results in an expansion/broadening of immunity. Also, the evidence would argue against this. This is because the immune response to mRNA vaccines is broad and involves a diverse repertoire of cells which is the ultimate goal of an effective viral vaccine.

Q: Should NZ be ordering boosters now? Isreal vaccinated at speed with Pfizer from eight months ago; they now have record new cases as vaccine effectiveness declined, and have opened up the booster shot for those aged 12+.
A: I would be cautious about the Israeli data. When you look more closely at the data, the vaccine is actually holding up very well in terms of effectiveness. There is a decline in the effect on transmission. They still have quite a large proportion of the population unvaccinated. Boosters are likely to have [value] in people at high risk of severe disease (elderly) and also people on the frontline who are at more risk of exposure.

Q: Can our health system sustain giving two vaccines and a booster (so three shots ) in one year? Do we have the staff and the money to do this without affecting other health services?
A: Good point! I do not think this would be a good idea for the reasons you mention and there is no indication for boosters (with few exceptions) at the moment. A good analogy by a WHO expert was that boosters are like throwing a third life jacket to someone who has two, while many people have no life jacket.

Q: Is it or will it be possible to obtain testing in NZ to see whether someone has built sufficient Covid-19 antibodies following vaccination? I am not sure that I will have built a sufficient immune response to the vaccination and potentially need a booster shot.
A: While a blood test can reveal you have made a nice immune response, we do not know what the cut-off levels are. You may have immunity but do you have enough to protect you? This space should evolve as we learn more from the trials. What you want to see is more IgG than IgM. As your immune response matures, your IgM will be low and IgG much higher.

Q: Can I have the vaccine injected into my thigh?
A: I imagine so, as long as it goes into the muscle. You would probably need to convince the vaccinator of why though!

Q: I believe everyone has a right to choose what medical treatment they have. But this could mean we never get to the point of having enough people vaccinated that lockdowns are no longer necessary. What are your thoughts on where our vaccination rates should be and what will happen if we don't get there?
A: I think we need to aim pretty high for this one, as in, up into the 90s per cent. Most people have had, are intending to have, or are thinking about having the vaccine which is good. We need to get enough [people] vaccinated so our hospitals are not swamped but will need very high rates in order to achieve community immunity and protect those who are not vaccinated. Looks like Delta is a heat-seeking missile and will find the vulnerable.

Q: Reports of a Covid variant worse than Delta have emerged. Any idea when a vaccine may become available against it? Also these strains seem to be getting worse by the month. Surely that cannot continue?
A: I have seen this. Yikes. I think some data about the potential impact on existing immunity will be out this week. Fingers crossed! ... The variants will slow when we have fewer infected people which is why we need to vaccinate all populations fast, not just a few.

Q: If Covid can be contracted and transmitted by fully vaccinated people who may be asymptomatic, how can we be sure it is eliminated in the community?
A: We need to keep testing to know what is happening in the community. Wastewater is another useful tool. Also, if it is widespread there will be cases in the unvaccinated and also some cases in the vaccinated. You can look at the US to see what this looks like.

Is it safe to be vaccinated if I have type-1 diabetes?
A: Yes! [There's] no increased risk of side effects.