Last week, the CEO of Pfizer said that anyone who receives his COVID-19 vaccine should probably have a third dose within 6-12 months after being fully immunized, and then probably one dose every year.
We will need it, because immunity is likely to decline for many of us within the time frame. The vaccine must also be adapted to cover new coronavirus variants as it occurs.
The advantage of mRNA vaccines like that of Pfizer is that it is much easier to update than the “viral vector” vaccines like AstraZeneca. We still have to use AstraZeneca for over 50s now, but our best long-term strategy is to use mRNA COVID-19 vaccines, and therefore develop the ability to manufacture them here in Australia.
Immunity to coronaviruses does not last
We know that our immunity to different coronaviruses decreases over time. This is true of the four common colds (endemic) coronaviruses that circulate all the time – there are always enough people who have lost their immunity to ensure that these viruses can persist and cause respiratory illnesses.
It also appears that our immunity to SARS-CoV-2, the virus that causes COVID-19, is rapidly declining, although the rate at which this is happening can be quite variable. Data suggest that the immunity gained with the Pfizer survey has been fairly strong for six months, but it is not clear how quickly our immunity is lost thereafter. However, it is reasonable to predict that within 12 months of a population being vaccinated, a significant number of people are likely to have lost protection against SARS-CoV-2. This will be especially the case if the prevailing SARS-CoV-2 strain circulating at the time differs significantly from the virus against which humans were originally vaccinated.
This is related to the fact that some coronavirus variants have mutations that reduce the effectiveness of the vaccine-induced immunity. It is described as a ‘variant of concern’ and contains a virus that originated in South Africa, which has reduced the effectiveness of both the AstraZeneca and Pfizer vaccines. As the pandemic increases worldwide, more variants will certainly emerge.
Both declining immunity and viral variants will work together to reduce our protection over time. So we need a boost survey, ideally updated to deal with the viral variant that poses the greatest threat.
Using AstraZeneca is not our best long-term solution
I understand why the Australian government originally chose the AstraZeneca vaccine. It is easier to manufacture, store and distribute. This made sense in the early stages of the pandemic. And it is still an effective vaccine that people, here and abroad, should receive as soon as possible – any immunity is better than no one and you will definitely be protected from severe COVID-19.
But over time, using the AstraZeneca shot is not the best long-term strategy.
One reason for this is what immunologists call “vector immunity.” The AstraZeneca and Johnson & Johnson vaccines use a viral vector, which is an inactivated form (which cannot be repeated) of a common type of virus called an ‘adenovirus’. They use this adenovirus as a delivery agent to get DNA into our cells to give the instructions to develop immunity to the coronavirus. However, you cannot be vaccinated repeatedly with this type of vaccine because you are likely to develop immunity to the adenovirus vector (the delivery vehicle) itself. When this happens, your immune system can interfere with the delivery vehicle in your cells, and the effectiveness of these vaccines will erode over time.
Peter Dejong / AP / AAP
What’s more, in a very, very small number of people, this viral vector appears to be linked to an extremely rare but severe blood clotting syndrome. In these people, it is thought that the result of the immune response to the viral vector is that their immune systems cause ‘auto-antibodies’. These are antibodies that, in addition to fighting a foreign invader (or the adenovirus-based vector used in the AstraZeneca vaccine), also attack our own cells. In this case, these autoantibodies attack blood cells called platelets, resulting in the blood clots and low platelets seen in about 1 in every 250,000 people vaccinated with the AstraZeneca shot.
There are also problems with the clotting of the Johnson & Johnson vaccine, which is also a vaccine based on adenovirus, after six women developed the condition in the United States out of 6.8 million. However, this link has not yet been proven for this vaccine.
Read more: What is thrombocytopenia, the rare blood condition possibly linked to the AstraZeneca vaccine?
In contrast, mRNA vaccines like Pfizer (and Moderna’s) can be updated much faster. Pfizer just needs to rework its RNA series to cover variants, which is a small change. Nothing changes to the delivery system of the vaccine, so the approval will probably be much easier. Regulators have indicated that there will be a quick way for approval for vaccines that are being updated for variants.
Read more: Why do we get COVID booster vaccines fast and know that they are safe?
The mRNA vaccines consist of a lipid-based delivery system that protects the mRNA and gets it into cells. Then the cells can produce the vein protein to host your immune system. There are no proteins in the vaccine itself, so there is no chance of developing immunity to the vaccine components.
mRNA vaccines are our best choice going forward
There is a fear among researchers, including myself, that we will chase our tails with these new variants. We will identify a new variant and be prepared to update our vaccines against it, but by the time the formulation is updated, approved, manufactured and distributed, we may already be dealing with another variant or many variants on different places.
It is imperative that Australia develops the ability to land mRNA vaccines, especially if new variants appear here or in our region. It will be much more effective than waiting months to get new shots from overseas.
Read more: Australia could miss several COVID vaccines if unable to make local mRNAs
Federal Health Minister Greg Hunt has indicated that Australia is interested in developing this capacity.
At present, the AstraZeneca vaccine still plays a role in Australia’s current vaccine strategy. We have it and we can make more of it, so let’s get it out there before the age of 50, and also give those under 50 the opportunity to make an informed choice to use this vaccine.
So few Australians currently have immunity to the virus; we remain vulnerable to outbreaks. If there are new outbreaks, we will have to rely on locks, masks and other strategies again and we can return to where we were last year. And let us not forget that some people will get sick and some will die. The effects of the vaccine are deteriorating, and we really need to catch up as soon as possible.
But over time, the AstraZeneca vaccine will become less attractive, and mRNA vaccines like those of Pfizer should eventually take its place.