Catching Covid-19 more than once – expert Q&A

The combination of vaccination and prior infection provides robust immunity against severe illness in future infections.

New Covid-19 variants and waning immunity could see more New Zealanders catching the virus for a second time.

As we head further from the peak of the vaccine campaign and the Omicron outbreak, people’s immunity will eventually start to wane. The coronavirus is also continuing to mutate, with subvariants like BA.4 potentially making it easier for people to be reinfected.

The Science Media Centre asked experts for the latest on Covid-19 reinfection.

Professor Michael Plank, Te Pūnaha Matatini and University of Canterbury, comments:

If someone has already had Covid-19, how well are they protected from getting it again?

“It’s tempting to think that getting Covid-19 means you “get it over with”. However, it’s likely that immunity against getting reinfected starts to wane after a few months and some people could be reinfected even sooner than that. It’s very likely we will continue to experience waves of infection driven by a combination of waning immunity and evolution of the virus. This is similar to what we see with flu and other seasonal illnesses, although Covid-19 is much more infectious than flu so remains a bigger public health issue.”

Will a second infection make someone more, less, or just as sick as the first time?

“For most people it’s a question of when – not if – they will next get infected with the virus. There’s no guarantee that second and subsequent infections will be milder than the first. But the good news is that the combination of vaccination and prior infection provides robust immunity against severe illness in future infections. Infection on its own without vaccination provides much weaker protection. This means it’s essential that you’re up to date with your vaccinations even if you’ve had Covid-19, otherwise you are needlessly risking serious illness the next time around.”

Do variants and sub-variants increase the chance of reinfection?

“New strains are emerging that may be able to reinfect people more easily. With borders open these variants are likely to quickly make their way into New Zealand, as has happened with the BA.4 sub-variant recently. This could mean we get a second wave sooner rather than later, although it’s not likely to be as dramatic as the way Omicron took over from Delta unless a completely new variant explodes onto the scene.”

Conflict of interest statement: Michael Plank is partly funded by the Department of Prime Minister and Cabinet for research on mathematical modelling of COVID-19.

Dr Anna Brooks, Cellular immunologist and Senior Research Fellow, Maurice Wilkins Centre, University of Auckland, comments:

If someone has already had Covid-19, how well are they protected from getting it again?

“Published studies on reinfections will take time to emerge given that the new variants/subvariants are all relatively recent. However Omicron and its subvariants partially evade our immune defences, meaning despite vaccine protection, symptomatic infections are relatively common. Even with our high vaccination rates and widespread Omicron outbreak, as long as we have more than one variant circulating, there will be a risk of reinfection. Immunity from our vaccinations or previous infection will also wane, leaving many at risk of infection.

“The figure of three months of immunity is largely a generalisation as cases of reinfection are definitely occurring within this time frame. Even if you’ve had Covid, you may have fairly decent immunity for at least a month or so, but you’re certainly not immune to further infections in the near future. The best approach is to avoid exposure, regardless of your vaccination or pre-infection status.”

Will a second infection make someone more, less, or just as sick as the first time?

“In NZ these reinfections are anecdotal as we are not actively tracking them, especially as the advice is to not retest within 90 days. However despite this, the cases we are hearing about (i.e. completely recovered, tested negative after their first infection and got another infection), are either similar or often worse. The symptoms are reminiscent of a new infection, i.e. not to be confused with ongoing symptoms more indicative of Long Covid.”

Does reinfection increase the risk of Long Covid?

“We are hearing from our international partners that anecdotally, repeat infections, especially in children and adolescents may lead to a higher chance of long term health complications, including Long Covid.

“It’s now been approximately two months since the Omicron peak and already we have an influx of people joining our research study and Long Covid support group, including families with children impacted by ongoing symptoms. Although the official time-frame for Long Covid is persisting symptoms beyond three months, some joining up have already experienced serious health complications, some requiring hospitalisation. Many still report having trouble getting adequate medical care. Many also don’t seem to realise that there are no treatments to reverse the debilitating symptoms experienced (shortness of breath, brain fog/cognitive impairment, extreme fatigue to name a few).

“We know that vaccinations are excellent at protecting against severe illness, however they aren’t great at reducing the risk of Long Covid. Protective immunity will also wane over time. Symptomatic infections, even while triple vaccinated are common. In addition, surviving one infection unscathed does not mean you will be out of the woods with getting Long Covid. It might be a 2nd or 3rd exposure that triggers this illness. Limiting exposure to the virus, even if previously infected and/or fully vaccinated is the best way to avoid the risk of developing long term health complications.”

No conflict of interest declared.

Dr Dianne Sika-Paotonu, Immunologist, Associate Dean (Pacific), Head of University of Otago Wellington Pacific Office, and Senior Lecturer, Pathology & Molecular Medicine, University of Otago Wellington, comments:

If someone has already had Covid-19, how well are they protected from getting it again?

“Many who’ve recovered from Covid-19 will have developed immunity at least for the initial months following infection, however re-infection risk with the SARS-CoV-2 virus remains. Although previous infection with the SARS-CoV-2 virus does offer some immune protection, this does wane over time.

“Importantly, recent evidence is indicating re-infections have been increasing with the Omicron variant of the SARS-CoV-2 virus.”

Will a second infection make someone more, less, or just as sick as the first time?

“In the UK, Covid-19 reinfection estimates from their Office for National Statistics indicated that reinfections with the Alpha variant produced symptomatic Covid-19 in 20% of cases, while reinfections with the Delta variant caused symptoms in 44% of cases and for Omicron, 46% of cases had symptomatic Covid-19 (-reinfections were defined as 120 days between positive tests or 4 subsequent negative PCR tests between infections). This data showed that people reinfected with the Alpha variant were much less likely to get symptoms the second time, when compared to their primary infection. Delta and Omicron reinfections however were more likely to cause people to experience symptoms.

“One study from Qatar looking at the re-infection severity after initial infection with the Alpha and Beta variants indicated that overall, SARS-CoV-2 re-infections (i.e. another infection occurring at least 90 days after the 1st infection), tended to be less severe when compared with the primary infection.

“Ongoing work will be needed to understand more about whether re-infections for Omicron and all its subvariants are more or less severe, when compared to the primary infection. It is still important that those who may have already had a Covid-19 infection, strengthen their immunity with vaccination as well.”

Do variants and sub-variants increase the chance of reinfection?

“A study from Imperial College London based on the UK Health Security Agency and National Health Service data showed that the risk of re-infection with Omicron was more than five times higher when compared with Delta.

“Monitoring for new variants will be important moving forward particularly with further easing of border restrictions, and will be especially important for managing potential future outbreaks caused by any new variants arising overseas. Community spread in Aotearoa New Zealand will be rapid if any new variants appear that are resistant to current Covid-19 vaccines.

“While issues with unequal global Covid-19 vaccine coverage, availability, accessibility and distribution persist, and remain unaddressed, new variants will continue to emerge, develop and spread.”

No conflict of interest declared.

ENDS.