When will I need my COVID vaccine booster shot? And can I switch to a different brand?

Nicholas Wood, University of SydneyAustralia’s vaccine rollout is really starting to gain pace, especially in New South Wales and Victoria.

We need to get two doses of vaccine into as many adults as possible — firstly because that helps reduce severity of illness and infection, but also because reaching vaccination targets is likely to bring some new freedoms.

The COVID-19 vaccines (Pfizer, Moderna and Astra Zeneca) continue to be highly effective in reducing risk of severe disease, hospitalisation and death, even against the Delta variant.

But as soon as we finish one vaccine rollout we may need to begin the next rollout of booster doses.

Read more:
Why is a third COVID-19 vaccine dose important for people who are immunocompromised?

When will I need my booster shot?

First, we need to differentiate between a booster dose and a third dose as part of the initial round of vaccinations. They are two very different things.

Some people who are immunosupressed might need a third dose as part of their primary COVID-19 vaccination schedule. In other words, their third dose comes not long after their second dose and is given to improve their initial protection.

A booster shot is given much later after the initial two dose round of shots. A good example is the way we give tetanus and whooping cough booster vaccines.

There’s a great explainer on who might need a third dose as part of their primary vaccination schedule over here.

For the rest of us, we don’t know for sure when you will need a booster shot. You’ll read lots of different figures on this — six months, eight months, more — and that’s because the research is ongoing. We don’t yet have a definite answer to the best timing for a booster dose.

Pfizer recently announced its research had shown a booster dose resulted an increase in antibodies against the initial virus as well as against the highly infectious Delta variant. These results are awaiting publication and the safety of the booster dose needs to be known. The European regulator (known as the European Medicines Agency) has also started to evaluate an application for the use of a booster dose of the Pfizer vaccine.

We know that there is a decline in antibodies after the primary course and some evidence of waning protection against infection.

In a recent letter to The New England Journal of Medicine, published online earlier this month, doctors and public health experts at University of California San Diego said their data suggested vaccine effectiveness against any symptomatic disease may wane over time since vaccination:

Vaccine effectiveness exceeded 90% from March through June but fell to 65.5% […] in July.

Read more:
How long does immunity last after COVID vaccination? Do we need booster shots? 2 immunology experts explain

Over time, data will emerge on immune responses and safety after a booster dose.

It may be that booster doses are particularly needed for certain groups in our community — for example, older people or frontline workers. There is also discussion of whether severely immunosuppressed people should get a booster dose from around six months after their third primary dose.

The US is planning to make COVID booster shots widely available to Americans from September onwards, starting eight months after people’s second dose of the Pfizer or Moderna vaccines.

The US booster plan is dependent on the Food and Drug Administration determining that a third dose of the two-dose vaccines is safe and effective, and following advice from the Centers for Disease Control.

Israel’s booster rollout has begun, with people there becoming eligible for a booster five months after their second dose.

The European Centre for Disease Prevention and Control recently said that there is

no urgent need for the administration of booster doses of vaccines to fully vaccinated individuals in the general population.

Can we mix and match, by getting a different brand of vaccine for the booster?

We don’t yet know for sure.

There may be benefits to getting a different vaccine to the one you first got as a booster. We also know that new vaccines designed specifically to target novel variants are in development and it may be better to receive a booster of a variant-specific vaccine.

It will be worth keeping a close eye on a key trial by the UK-based COV-BOOST group, which is aiming to find out which vaccines against COVID-19 are most effective as a booster vaccination, depending on which vaccine was used to provide the initial primary vaccine course.

This study will give us good information on whether it will be better to get a booster shot that is the same brand as your primary dose, or whether to switch to another.

For example, should a person who initially got Pfizer for their first two doses get an AstraZeneca shot for their booster? Or vice versa? Or should they get a booster of a new variant vaccine?

A trial is underway in the US looking at the safety and immune responses of using a different booster vaccine to the first two doses, but also includes a Beta (B.1.351) variant vaccine.

It’s possible mixing and matching different vaccines might broaden your protection — but the research is ongoing, and it’s too early to say.

Hopefully, supply chain issues for the Pfizer vaccine will improve in the coming months.

The prime minister recently announced Australia has secured an extra four million doses as part of a deal with the UK, on top of extra doses coming as part of deals with Singapore and Poland.

This will help with the rollout of initial doses.

For now, the priority is getting the two doses into arms

Monitoring of the effectiveness of the COVID vaccines will continue, particularly against the delta variant and any new variants that emerge.

Trials are also underway of the safety and immune responses to a variety of different booster vaccines, including the next generation variant vaccines.

The World Health Organization said in August:

In the context of ongoing global vaccine supply constraints, administration of booster doses will exacerbate inequities by driving up demand and consuming scarce supply while priority populations in some countries, or subnational settings, have not yet received a primary vaccination series.

The focus for the time being remains on increasing global vaccination coverage with the primary series.

For now, Australia must focus on getting our primary adult coverage as high as possible in order to protect against severe disease, hospitalisation, and death.

Read more:
Why we’ll get COVID booster vaccines quickly and how we know they’re safe

The Conversation

Nicholas Wood, Associate Professor, Discipline of Childhood and Adolescent Health, University of Sydney

This article is republished from The Conversation under a Creative Commons license. Read the original article.

How long does immunity last after COVID vaccination? Do we need booster shots? 2 immunology experts explain

Vasso Apostolopoulos, Victoria University and Jack Feehan, Victoria UniversityAn important factor in achieving herd immunity against SARS-CoV-2 (the virus that causes COVID-19) is is how long the vaccines protect you.

If a vaccine continues to work well over a long period, it becomes easier to have a significant proportion of the population optimally protected, and in turn suppress or eliminate the disease entirely.

As the rollout of COVID-19 vaccines continues, public attention is increasingly turning to booster shots, which aim to top up immunity if it wanes. But is a third dose needed? And if so, when?

Let’s take a look at what the data tell us so far about how long immunity from COVID-19 vaccines might last.

First, what about immunity following COVID-19 infection?

The presence of antibodies against SARS-CoV-2 is used as an indicator of immunity, with higher levels indicating greater protection. Once antibody levels drop below a particular threshold, or vanish completely, the person is at risk of reinfection.

Initially, scientists observed people’s antibody levels rapidly decreased shortly after recovery from COVID-19.

However, more recently, we’ve seen positive signs of long-lasting immunity, with antibody-producing cells in the bone marrow identified seven to eight months following infection with COVID-19. In addition, scientists have observed evidence of memory T cells (a type of immune cells) more than six months following infection.

A study of over 9,000 recovered COVID-19 patients in the United States up to November 2020 showed a reinfection rate of only 0.7%. These findings closely align with a slightly more recent study suggesting reinfection after COVID-19 is very uncommon, at least in the short term.

Read more:
5 ways our immune responses to COVID vaccines are unique

While it seems likely there’s some level of lasting protection following COVID-19 infection, if you’ve had COVID, getting vaccinated is still worthwhile.

There’s some evidence vaccination after recovery leads to a stronger level of immunity compared to “natural” immunity from infection, or immunity from vaccination alone. People with so-called “hybrid immunity” appear to exhibit a more diverse range of antibodies.

How long does immunity from vaccines last?

The vaccines deployed against COVID-19 in Australia and most of the western world come from two classes.

Those produced by AstraZeneca and Johnson & Johnson are viral vector vaccines. They use an adenovirus (which causes the common cold) to prime the immune system to respond to SARS-CoV-2.

The vaccines developed by Pfizer and Moderna use mRNA-based technology. The messenger RNA gives your cells temporary instructions to make the coronavirus’ spike protein, teaching your immune system to protect you if you encounter the virus.

For the viral vector vaccines, despite ongoing trials, there’s little data available on the duration of the antibody response. The original studies showed efficacy for one to two months, however the duration of protection, and whether a booster will be needed, require further evaluation.

Notably, a vaccine similar to AstraZeneca against a related coronavirus (Middle East respiratory syndrome, or MERS) showed stable antibody levels over a 12-month follow-up period. This gives hope for lasting protection against similar coronaviruses.

Read more:
How well do COVID vaccines work in the real world?

The Pfizer and Moderna COVID-19 vaccines are the first vaccines based on mRNA technology to be approved for human use. So there’s still significant research required to evaluate the nature and duration of immunity they induce.

Interestingly, “germinal centers” have been identified in the lymph nodes of people vaccinated with the Pfizer vaccine. These act as training sites for immune cells, teaching them to recognise SARS-CoV-2, indicating a potential for long-lasting protection.

Initial studies only evaluated short-term efficacy, however recent research has found strong antibody activity at six months.

What about Delta?

Variants such as Delta, which are more transmissible and potentially more dangerous, are likely to increase interest in booster programs.

All vaccines show modestly reduced efficacy against Delta, so any decrease in protection over time could be more problematic than with the original SARS-CoV-2 virus, or other variants.

A recent preprint (a study yet to undergo peer review) found protection against the Delta variant waned within three months with both the Pfizer and AstraZeneca vaccines.

This research from the United Kingdom showed the Pfizer vaccine was 92% effective at preventing people from developing a high viral load at 14 days after the second dose, but this dropped to 78% at 90 days. AstraZeneca was 69% effective against the same measure at 14 days, dropping to 61% after 90 days.

This study shows vaccinated people who become infected with Delta still carry high amounts of virus (viral load). Third booster doses will be important to reduce these breakthrough infections and subsequent transmission.

Read more:
Why do we need booster shots, and could we mix and match different COVID vaccines?

Although the UK study looked at infections rather than hospitalisations or deaths, data from around the world continue to show the unvaccinated are making up the vast majority of patients who develop serious illness.

Nonetheless, scientists are continuing to investigate how waning immunity could affect protection against the more serious outcomes of COVID-19.

OK, so what now?

Pfizer has reported positive results from trials of a third dose to boost immunity, and the company is seeking formal approval for a booster from the United States Food and Drugs Administration.

The United States has announced it will begin distributing third doses next month to people who received an mRNA vaccine eight months ago or more.

Other countries, such as Israel, have already begun rolling out boosters. The move to offer third doses in some high-income countries has raised ethical concerns, with many people around the world still unable to access a first or second dose.

A number of countries have authorised booster doses for at-risk populations in response to the rise of the Delta variant.

This includes older adults and those with compromised immune systems, to combat the increased risk of severe disease and diminished vaccine protection in these people.

In Australia, there is likely to be a booster program in the future. But given the current issues surrounding supply, it’s unlikely to be for some months.The Conversation

Vasso Apostolopoulos, Professor of Immunology and Associate Provost, Research Partnerships, Victoria University and Jack Feehan, Research Officer – Immunology and Translational Research, Victoria University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Why is a third COVID-19 vaccine dose important for people who are immunocompromised?


Emily Edwards, Monash University and Kylie Quinn, RMIT UniversityA number of countries including the United States and the United Kingdom are moving to make a third dose of COVID-19 vaccine available to people who are immunocompromised.

But why are people with weaker immune systems at the front of the queue for a third dose?

As we continue to roll out COVID-19 vaccines around the world, emerging data is showing those who are immunocompromised aren’t necessarily as well protected by the first two doses.

So for these people, a third dose, sooner rather than later, could be particularly beneficial.

First, who is ‘immunocompromised’?

People who are immunocompromised have conditions called immunodeficiencies, where part of their immune system is missing or not functioning as well as it should.

Around 2.8% of adults in the US are immunocompromised. We expect the rate is similar in Australia.

Immunodeficiencies are broadly divided into two categories:

  • primary immunodeficiencies are very rare, often inherited conditions caused by mutations in our DNA
  • secondary immunodeficiencies are more common and are acquired after birth. Factors that can cause secondary immunodeficiency include malnutrition, certain infections, cancer, and some drug treatments.

Read more:
Why do we need booster shots, and could we mix and match different COVID vaccines?

Immunodeficiencies vary in severity, depending on what part of the immune system is missing or the degree of function lost.

The moderate to severe end of the spectrum includes serious forms of primary immunodeficiencies, untreated human immunodeficiency virus (HIV) infection, organ or bone marrow transplant recipients, and people treated with chemotherapy or high doses of immunosuppressive drugs.

We know severely immunocompromised people are susceptible to more severe and prolonged illness with COVID-19.

A man receives a vaccination.
A person undergoing cancer treatment could be immunocompromised.

How well do COVID-19 vaccines work in immunocompromised people?

A preprint (a study yet to undergo peer review) from the UK shows the Pfizer and AstraZeneca vaccines are 73% and 74.6% effective in preventing symptomatic COVID-19 in immunocompromised people respectively.

However, several published and emerging studies are reporting that people who are severely immunocompromised have very high rates of “breakthrough” infections (where people become infected despite being fully vaccinated). This clearly signals COVID-19 vaccines aren’t working optimally in this group.

Some people with primary immunodeficiencies can generate immune responses to COVID-19 vaccines, but these responses tend to be lower than what we’re seeing in healthy people. This decreased immunity could lead to increased breakthrough infections.

Normally, after one dose of the Pfizer vaccine, nearly 100% of healthy people will make detectable levels of antibodies against the virus.

But in a trial with organ transplant recipients, only 4% of people generated a detectable immune response after one dose, increasing to 40% after two doses and 68% after three doses.

So a third dose is likely to provide significant benefit to severely immunocompromised patients.

Read more:
We don’t yet know how effective COVID vaccines are for people with immune deficiencies. But we know they’re safe — and worthwhile

Notably, immunocompromised people are already given additional doses of some vaccines.

For example, it’s recommended people who have received a bone marrow transplant receive two doses of the influenza vaccine in the first year after the transplant, instead of the usual single dose.

What about third doses in other people?

In addition to classic immunodeficiencies, ageing can lead to a modest immune deficit. In turn, older people are more susceptible to some infections, including COVID-19.

Studies with the Pfizer vaccine show immune responses are lower in older people compared to younger people. Pfizer has shared early data showing a third dose of their vaccine can increase immunity in 65 to 85-year-olds.

Some countries are starting to offer third doses to older people. For example, Israel started delivering third doses to people over 60 in late July (before opening boosters up to younger age groups during August).

However, double and even single doses of the Pfizer or AstraZeneca vaccines very effectively protect against severe disease with COVID-19 among older people. So it’s still unclear whether this is urgently needed.

A third dose for all ages could ultimately be used to generate optimal immunity against COVID-19. Some preprint studies suggest immunity can modestly decline by about three months after the second dose.

Pfizer has shared preliminary data showing a third dose can boost immunity in healthy people.

But the rollout of third doses to a broader range of people in higher-income countries has implications for vaccine equity. The World Health Organization Director General, Tedros Adhanom Ghebreyesus, has led calls to pause third doses until more people in lower and middle income countries are able to access vaccines.

However, he specified immunocompromised people should have access to a third dose.

When might third doses be offered in Australia?

In Australia, a third dose of a vaccine may be offered to immunocompromised people, and possibly eventually to everyone. Some media reports have suggested this may be months away. Health Minister Greg Hunt has indicated current vaccine agreements have factored in the possibility of boosting.

A shift to third doses would need approval from the Australian regulatory and vaccine advisory bodies, and would probably focus on immunocompromised and other high-risk people initially.

A third dose of a variant-specific vaccine could also be an option in the future. These vaccines can deliver an updated version of the virus “antigen” — the target our immune system learns to recognise on the surface of the virus — to refocus our immune system on new strains like Delta.

This approach would be similar to our yearly update of the flu vaccine. Pfizer, Moderna and other vaccine manufacturers have variant-specific COVID-19 vaccines in clinical testing.

Read more:
Immunocompromised people make up nearly half of COVID-19 breakthrough hospitalizations – an extra vaccine dose may help

Even with a third dose, other measures will continue to be important in protecting immunocompromised people from COVID-19. These include “shielding” (staying at home and minimising face-to-face contact with others), immunoglobulin replacement treatment (which replaces antibodies needed to fight disease), and high vaccine uptake among the rest of the community.

But it’s clear a third dose would be uniquely beneficial for this group.The Conversation

Emily Edwards, Research fellow, Allergy and Clinical Immunology Laboratory, Monash University and Kylie Quinn, Vice-Chancellor’s Research Fellow, School of Health and Biomedical Sciences, RMIT University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Coronavirus Update: Australia

Novavax is absent from Australia’s 2021 vaccination schedule. But it could be a useful booster later on

Cassandra Berry, Murdoch UniversityNovavax recently released excellent results from phase 3 clinical trials, finding its COVID-19 vaccine demonstrated 90.4% efficacy overall after two doses given three weeks apart.

The results, from close to 30,000 people in the United States and Mexico, found the vaccine demonstrated 100% protection against moderate and severe COVID-19, and was highly protective against circulating variants of interest and concern. It also has a good safety profile.

It’s important to note these results came directly from Novavax in a press release, and we’re still waiting to see the data published in a peer-reviewed journal. Once this happens, it’s likely Novavax will apply for approval from medical regulators around the world.

But this process will take a few months. The Therapeutic Goods Administration has said it doesn’t expect to receive the final data it needs to approve the vaccine until September. And in the COVID Vaccination Allocation Horizons, information the government released this week setting out vaccine allocation until the end of 2021, Novavax is not mentioned.

So by the time Australia is ready to deliver Novavax — the country has 51 million doses on order — we may well have completed most of the vaccine rollout with the AstraZeneca, Pfizer and Moderna vaccines. The situation will be similar in other countries, such as the United States.

However, that doesn’t mean Novavax won’t play an important role in Australia’s fight against COVID-19.

How does Novavax work?

Novavax is designed using protein-based technology. This is different from the AstraZeneca vaccine, which is a viral vector vaccine, and Pfizer and Moderna, which use mRNA technology.

Novavax works by introducing a part of the SARS-CoV-2 virus — the spike protein — to the immune system. The spike protein used is made in insect cells and doesn’t contain any live components of the virus. It can’t replicate or cause COVID-19.

To help the vaccine generate a stronger protective response, it uses an adjuvant, which is a molecule that boosts the immune system. The adjuvant Novavax uses is based on saponin, a natural extract from the Chilean soapbark tree.

An illustration of SARS-CoV-2.
COVID-19 vaccines work by targeting the spike protein, a protein on the surface of SARS-CoV-2.

In some countries, Novavax could be used as an initial COVID vaccine. It will be relatively easy to distribute because it can be stored at regular fridge temperatures.

In other countries where most people will have already received two vaccine doses by the time Novavax becomes available, the vaccine could be used as an annual booster — on its own or as a supplement in formulated vaccines.

Read more:
What is Novavax, Australia’s third COVID vaccine option? And when will we get it?

A potential booster

Let’s say you’re writing a book. You write your first draft — that’s the first dose of vaccine. Then you edit and refine the final draft — that’s the second dose. You could say annual booster vaccines are like updated editions. Perhaps the original book is also translated into different languages, just as boosters could cover viral variants around the world.

In slightly more scientific terms, after the first vaccine dose, certain cells in our immune system (normal B cells) are activated and produce a primary antibody response. After the second vaccine dose, a slightly different flavour of immune cells (memory B cells) mount a stronger antibody response more rapidly.

But this immune memory can wane over time. Boosters may be needed to enhance immune memory responses to the SARS-CoV-2 spike protein in people who have previously been vaccinated against COVID-19.

Boosters could also be important as new variants emerge. Vaccines can often be reformulated to protect against new viral variants when original formulations aren’t working as well.

So even if Novavax isn’t the first or second COVID vaccine in our arms, it could be an important tool in our arsenal as we continue to navigate the pandemic.

A person with a bandaid on their upper arm.
Novavax could potentially be used as a booster vaccine down the track.

What about in combination with the flu shot?

Novavax has recently revealed the efficacy of its COVID vaccine was roughly the same in a study where an influenza vaccine was administered simultaneously. This data, although yet to be peer-reviewed, signals Novavax could potentially be given alongside the annual flu shot.

In the future, we could even have the flu shot and Novavax combined in one vaccine. Novavax has designed and is currently testing a vaccine which combines SARS-CoV-2 and influenza spike proteins (called a multivalent vaccine).

Read more:
Can I get AstraZeneca now and Pfizer later? Why mixing and matching COVID vaccines could help solve many rollout problems

SARS-CoV-2 is rapidly evolving and we need to future-proof Australia against viral variants. As our knowledge of COVID-19 builds, we must develop strategies for more robust protection.

Rather than a fast sprint, our immune systems likely need to be primed for an ultra-marathon. Thinking about vaccines beyond the “first wave” of vaccination will be key.The Conversation

Cassandra Berry, Professor of Viral Immunology, Murdoch University

This article is republished from The Conversation under a Creative Commons license. Read the original article.