Q&A: What’s the story with Omicron and waning immunity?

Vaccines and previous infection with Covid-19 are no guarantee against reinfection

There are shocking indications of Covid-19 reinfection at present. The virus is affecting those who have previously had Covid-19 and also people who have been double vaccinated. This seems to be the calling card of the Omicron variant - it is not only far more infectious than predecessors, it is also is causing reinfection at an alarming rate.

Mutations mean its spike protein looks different from that of the original strain current vaccines were designed to target. Antibodies from previous infection and vaccination will be less efficient at intercepting Omicron. Because they stick to the virus less vigorously, a higher quantity of antibodies is also required to compensate for them being less well matched.

The same applies to antibodies post-infection. Omicron has eradicated any well-meaning but misguided notion among previously infected people that “we have had our Covid dose, so we can go mad at Christmas and meet whoever we wish, safe in the knowledge we cannot contract it again in the short term”.

How is waning immunity adding to the threat?
What's not helping is confirmation of waning immunity with all currently used vaccines, with some showing signs of weakening antibody strength faster than others.


Current circumstances point to the paramount need to get a third “booster” dose as quickly as possible, as that combination re-strengthens immunity hugely. It also underlines the heightened vulnerability of unvaccinated people. One in six Irish people are unvaccinated; more than one million over-40s have yet to come forward for their booster.

A UK study to be published in coming days illustrates the precarious position the world is in right now. At one level, it provides reassurance, as it shows those who fall ill with Omicron are less likely to become severely sick than those who contract Delta – the first early, real-world data on disease severity.

Though Omicron cases in Britain seem to be milder overall, the UK Health Security Agency (UKHSA) concludes it is not necessarily mild enough to avoid large numbers of hospitalisations, according to its data.

The UKHSA is reported to conclude that while two doses of a Covid vaccine are not enough to offer strong protection against Omicron, a booster dose significantly reduces chances of symptomatic infection and hospitalisation.

What of those who have previously had Covid-19?
Worryingly, there are indications people who have had Covid in the past six months are also missing out on getting a booster. Research by Imperial College London shows protection may be as low as 19 per cent against Omicron among those who have had the disease, whereas with other variants 85 per cent protection applied.

In such circumstances, the risk of reinfection is 5.4 times greater than that from the Delta variant, according to UCD virologist Dr Gerald Barry. So a false sense of security, which to an extent you might have got away with previously, no longer applies.

Is a fourth jab now looking inevitable?
Israel is set to become the first country in the world to offer a fourth dose of vaccines in an effort to protect against Omicron. People over the age of 60 and healthcare workers will be eligible for a second booster shot.

Ireland will watch that space, chief medical officer Dr Tony Holohan confirmed on Wednesday. So if it proves necessary, we will follow that course. There is every indication continued use of boosters will apply, if Covid infection waves recur. Likewise, if Omicron is shown to be considerably more dangerous, Omicron-targeted versions of Covid-19 vaccines will be developed; in some cases, they can be ready within months.

What is the latest advice for the festive period?
The Omicron variant accounts for two-thirds of confirmed Irish cases, so there is no room for complacency even if Christmas is a relentless push towards socialisation.

Dr Holohan warned on Wednesday public health teams are reporting a higher level of infection among household close contacts – while a surge in 16- to 34-year-olds is inevitable.

The need to get tested if showing signs of infection is especially important – and to self-isolate and book a PCR test either by phone or online.

Antigen tests are for use where there are no symptoms when going out or meeting people, and self-isolation must apply with any positive result.

In the meantime, while we wait for a definitive indication of whether Omicron is less severe or not, increased transmissibility remains the most immediate and growing threat.