How worried should we be about COVID-19 breakthrough infections?

The idea of breakthrough cases is not a new concept. With COVID, these infections are not a reason to turn down the offer of a vaccine.

[Muaz Kory/Al Jazeera]

As the pandemic rages on, new buzzwords and phrases find their way into our daily vernacular – and one that is currently doing the rounds is “breakthrough infection”. This term refers to COVID-19 infections that occur more than 14 days after someone has been fully vaccinated; it does not refer to the severity of illness suffered from the disease but implies that a person has tested positive for the virus.

On the surface of it, this may appear rather worrying – but do not forget the purpose of the COVID vaccines is not to make you immune to the virus (they never claimed to do that), but to protect those vaccinated from severe illness and hospitalisation should they contract the virus. Since no COVID vaccine is 100 percent effective, some infections in fully vaccinated individuals are expected. However, these appear to be uncommon, and a high proportion may be asymptomatic.

Generally speaking, those who have been fully vaccinated may still pick up the virus, but the immune response triggered by the vaccines means they are only likely to have mild if any symptoms at all. For instance, in an American study looking at military personnel who had been fully vaccinated and got breakthrough infections, none of them needed hospital treatment.

People who become infected with SARS-CoV-2 after being vaccinated against it are likely to have milder and shorter illnesses. This is because their immune systems have been primed by the vaccine to recognise the coronavirus that causes COVID-19 and to destroy it and any cells it has managed to invade before it has a chance to make them unwell – even though they can still test positive for the virus.

The fact that there are still high levels of coronavirus circulating in the general population means a higher chance of those fully vaccinated coming into contact with it and getting a breakthrough infection, albeit with milder symptoms.

Prior to the emergence of the Delta variant, it was thought that those who were fully vaccinated were less likely to pass the virus on to others as they had lower “viral loads” – this refers to the amount of virus a person is carrying; the higher the amount of virus or “viral load” the more infectious the person is. However, whether or not this is still true when it comes to the Delta variant is under review, but it is likely that even with Delta, breakthrough infections are likely to be milder in those vaccinated than those unvaccinated.

We are likely seeing an increase in breakthrough infections because fully vaccinated people are able to mix more as restrictions across countries with high vaccination rates ease.

It is thought that the vaccines trigger less of a robust response in older people, thus we are seeing larger proportions of breakthrough infections in those aged 65 and over. Having a weakened immune system may also increase the risk of getting a breakthrough infection, despite being fully vaccinated – such as those who are on treatment for cancer and those who are on medication that dampens down their immune systems because of other underlying health conditions.

The emergence of the Delta variant has also increased the risk of breakthrough infections as both the mRNA vaccines (Pfizer and Moderna) and the AstraZeneca vaccine are less effective against Delta when compared with the “wild” or original variant and the Alpha variant.

The fact that there are still high levels of coronavirus circulating in the general population means a higher chance of those fully vaccinated coming into contact with it and getting a breakthrough infection, albeit with milder symptoms.

[Muaz Kory/Al Jazeera]

But it is important to note that the idea of breakthrough infections is not a new concept, and in relation to COVID-19, these infections are certainly not a reason to turn down the offer of a vaccine.

We see breakthrough infections in many other diseases we vaccinate against because no vaccine is 100 percent effective. The gold standard of vaccines is the mighty MMR vaccine (measles, mumps, rubella). Two doses of MMR vaccine are 97 percent effective against measles and 88 percent effective against mumps. This means about three out of 100 people who get two doses of the MMR vaccine will get measles if exposed to the virus. However, they are more likely to have a milder illness and are also less likely to spread the disease to other people. The fact that so many people are vaccinated against measles reduces the risk of breakthrough infections. Mumps outbreaks can still occur in highly vaccinated communities, particularly in settings where people have close, prolonged contact, such as universities and close-knit communities.

Breakthrough infections are even more likely with the seasonal flu virus even in those vaccinated against it – flu vaccine efficacy rates vary from year to year depending on the strains they are targeting that year but they generally vary from 40-60 percent – meaning breakthrough infections are relatively common.

Groups and individuals who are opposed to the idea of COVID vaccines point to breakthrough infections as another reason not to get vaccinated, but that argument is specious. The vaccines were never about 100 percent protection from the virus; no vaccine can boast that efficacy. They have always been about reducing the severity of symptoms, and significantly lowering the risk of needing hospitalisation from COVID – and they are still excellent at doing this even with the highly transmissible Delta variant to contend with.

Breakthrough infections remain a reality for all diseases that we have vaccinated against, the key is getting enough of the world vaccinated to help reduce the number of breakthrough infections and protect the most vulnerable in society. That has been the mantra for all vaccination programmes that have come before and is still the mantra for the COVID vaccination programme.

Progress Report: The Lambda variant

While most of us have been focused on the Delta variant that first emerged in India and spread rapidly through Europe, the US and Asia – in South America another variant has been gathering momentum.

The Lambda variant, also known as C.37 and first identified in Peru as early as August 2020, is now present in more than 30 countries and is dominant in Argentina, Colombia and Chile. Studies have shown that specific mutations on its spike protein make it more infectious than the Alpha variant. The World Health Organization (WHO) has declared the Lambda variant a “variant of interest” as of June 2021.

[Muaz Kory/Al Jazeera]

The rate at which the Lambda variant has spread through Peru and other Latin American countries has meant many governments across the world are now spooked by it. Much of the concern has come from mutations occurring on the spike protein of the Lambda variant of the virus. The spike protein is the part of the virus that juts out and allows it to bind to human cells, merge with them and then enter them causing them to become infected.

A study that is awaiting peer review describes a mutation on the spike protein of the Lambda variant, known as L452Q, which might mean the variant is twice as infectious as the original or “wild” variant of the coronavirus. This mutation is similar to the L452R mutation that helps make the Delta variant so transmissible.

There is also growing concern about whether the vaccines are less effective against the Lambda variant. A preprint study (not yet peer-reviewed) by investigators in Chile suggests that the mutation is highly infectious, and may also be able to evade vaccine antibodies triggered by the Chinese produced CoronaVac vaccine – a vaccine that has been used widely in South America. There is little research currently looking at the effectiveness of the Pfizer or Moderna vaccines against Lambda, but they are thus far thought to offer effective protection against severe disease from the variant.

Much of Latin America remains unvaccinated, and while richer countries continue to have highly successful vaccination programmes that protect their own populations, we are going to see new variants arise in countries that rely on vaccine donations to help them protect their populations.

We are in a race against the virus. We must vaccinate as much of the world as possible, as unvaccinated populations are breeding grounds for COVID. And where the virus breeds, it has a high risk of mutating – which will be a problem for us all.

Good News: Identifying high-risk patients with vaccine-induced blood clots

Much was made of the very rare link between the Oxford-AstraZeneca COVID vaccine and what is now called vaccine-induced thrombocytopenic thrombosis (VITT). Thrombocytopenia is a condition where the number of proteins (called platelets) in your blood drop; these help the blood to clot and when numbers drop there is a risk of bleeding. Thrombosis means blood clots and VITT can lead to both a bleed and a clot, which can be very dangerous. Although these clots can occur anywhere in the body, there was particular concern about those that occurred in the blood vessels draining blood from the brain.

Scientists at Oxford University have been looking at better ways to identify those admitted to hospital with these very rare blood clots. They identified the most common symptoms, as well as those who were at the highest risk of death from the rarer clots. The research showed that the overall mortality or risk of death from this rare condition was about 23 percent, though this increased significantly in those who had a very low platelet count and bleeding on the brain following blood clots.

The authors of the study were anxious to point out that the risk of developing a clot or a bleed after getting the AstraZeneca vaccine remains rare; in those aged under 50, the incidence is about 1 in 50,000 people who have received the vaccine.

[Muaz Kory/Al Jazeera]

It remains important that those who did have symptoms were recognised early and treatment started as soon as possible. Dr Sue Pavord of Oxford University Hospitals (OUH) NHS Foundation Trust, who led the research, said, “We have worked relentlessly to understand and manage this new condition so that the hugely successful vaccine rollout can continue, which is the most viable solution to the global pandemic.”

In the Doctor’s Surgery: Is it time to start ‘living with the virus’ now that much of the adult population has been vaccinated?

I was recently asked this question on national television, and I was torn between being a healthcare professional who has seen the devastating effects of COVID and one who has seen the huge mental health effects that repeated lockdowns in the UK have had on my patients.

The UK has had a successful vaccine rollout, mainly due to the hard-working people of the NHS. It is estimated that more than 75 percent of the adult population has been vaccinated and we are now turning our attention to 16- and 17-year-olds. Unlike many other developed nations, the UK has decided to hold off vaccinating those aged 12 to 15 until more data, specifically around inflammation of the heart, becomes available. This has angered many scientists and healthcare professionals.

Children are, of course, less likely to suffer serious illness from the virus, though that is not an absolute rule. We are seeing large numbers of children in the US admitted with serious illness from COVID and there is a significant cohort of immunocompromised or clinically extremely vulnerable children with underlying health conditions that make them particularly susceptible to the effects of the virus.

Time is not a luxury many of my patients can afford … so a balance must be struck. And therein lies the problem: whatever decision is made, someone will suffer.

On the other hand, so many people have suffered financially, socially and mentally from the effects of the lockdowns and have welcomed the easing of restrictions across the UK. I have spoken with many patients who have lost their livelihoods because of the lockdowns and, as a result, are now suffering from significant mental health issues. Children have suffered terribly due to schools being closed at the height of the pandemic, and recent exam results reveal a widening gap between children from wealthy backgrounds and those from poorer ones, a gap that will take years to close. That, too, will have a knock-on effect on the health of these children as they develop into adults.

So as a generalist who sees both sides of the argument, it was a difficult question for me to answer. Ideally, I would like more time to vaccinate more of the adult population; I would advocate for vaccinating those aged 12-15; I would like to see the effect that schools reopening in the autumn term has on the spread of the virus, and I would like to see if the combination of easing of restrictions and change of seasons into the autumn and winter period leads to an increase in infections.

But time is not a luxury many of my patients can afford – people who run businesses, or who are struggling to put food on the table due to the lack of income they have had to endure over the last eighteen months – so a balance must be struck. And therein lies the problem: whatever decision is made, someone will suffer.

Reader’s Question: If I test positive for COVID but don’t have any symptoms, will I still be able to pass it on to others?


Although people with no symptoms are probably less infectious than those with symptoms, they can still pass the virus on to others. It is also worth noting that the peak time at which you can pass the virus on is 1-2 days before your symptoms develop.

There is a concern that those without symptoms have played a large part in spreading the virus, so countries like the UK have advised regular lateral flow rapid tests – even if you do not have symptoms – to see if you are carrying the virus.

Do not assume that because you don’t have symptoms you are not a risk to others – you could still be.

Source: Al Jazeera