Cases where people have had COVID-19 twice, or where they’ve been infected despite being fully vaccinated, have naturally given rise to doubts about how long immunity lasts, whether booster shots will be necessary, and whether the approved vaccines available today will still be effective against new strains that may emerge next year – or next month.

There’s some good news, but also some not-so-good news.

How long will immunity last?

In early 2020, when little was known about the virus that causes COVID-19, the hope was that once you’d had the disease, you’d be immune. Likewise, it was hoped that when scientists had developed a vaccine, after being vaccinated then you’d enjoy long-term immunity.

Cases where people contracted COVID-19 twice were not unknown but appeared to be very rare. Now, it seems such cases are becoming more common, though the evidence so far is ambiguous, and it may still be relatively rare (at less than 1%).

The human immune system has been described as being rather like our own memory – it clearly remembers some infections but forgets others. With a ‘highly memorable’ infection (like measles, for example), you’ll probably have lifelong immunity after a single bout of it.

With COVID-19, however, this doesn’t seem to be the case. A recent study showed that most people – but not everyone - who’d had the disease were protected from contracting it again for at least five months. Many of the people who were reinfected had no symptoms, but they still had high levels of virus in their noses and mouths and were likely to infect other close contacts.

What are ‘breakthrough cases’?

This term refers to cases of people getting infected after vaccination. They’re known as ‘breakthrough’ infections because the virus ‘breaks through’ the protective barrier provided by the vaccine.

The latest advice from the US Centers for Disease Control and Prevention is that vaccination is recommended even after infection with COVID-19, because unvaccinated people are more than twice as likely to get COVID-19 again.

How long will my vaccination protect me?

The virus that causes COVID-19 – known as SARS-CoV-2 – is evidently one of those that keeps mutating and producing different strains or variants that behave differently and can cause a different array of symptoms. This raises the question as to whether there will have to be an ongoing ‘arms race’ between the capacity of the virus to develop new and different variants – and possibly evade vaccines – and the ability of scientists to keep ‘tweaking’ the vaccines so that they remain effective against the latest variant of the virus.

This is the good news – while existing vaccines may not provide as much protection against emerging variants, many infectious disease experts are optimistic that vaccines could be rapidly ‘reprogrammed’ to remain effective against new variants.

Booster shots

The upshot of all this is that given the fact immunity evidently wanes over time, and given that – like the flu – the virus can be expected to go on evolving and giving rise to new variants, it may be that COVID-19 vaccinations will become a regular feature of our lives, much as flu vaccinations already are, for many of us.

Booster shots are already being recommended for people with compromised immune systems, according to Dr Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, and this is the focus of much of the public discourse about booster shots – whether certain sectors of the population could benefit from them in the short term.

However, hundreds of new vaccines are in various stages of development, including here in Australia, for example, at the Westmead Institute for Medical Research. Some of the second-generation, booster vaccines currently in the pipeline employ different strategies for tackling the virus, and it’s hoped that some of them will deliver longer-term, broader immunity, better protection for older people, and greater effectiveness against future new variants.

It remains to be seen whether in the longer term, if supply eventually catches up with demand, regular COVID-19 vaccinations are added to the list of immunisations already recommended by Australian health authorities.

This content is not intended to be a substitute for professional medical advice and should not be relied upon as health advice. Always seek the advice and guidance of your doctor or other qualified health professional with any questions you may have regarding your health or a medical condition.