Covid-19 vaccine: Will we need a booster shot and when?

With the successful rollout of Covid-19 vaccines to a significant proportion of the population and the promise of everyone in the State being vaccinated by the end of September, the next issue on the immunisation front is the need for booster vaccines.

What is a booster dose? Some vaccines, such as tetanus, are recommended every 10 years. Boosters are a reminder to our immune system; if we become exposed to a toxin, it will remember and respond quickly.

Here are some of the many questions that experts in the National Immunisation Office (NIO) and the National Immunisation Advisory Committee (NIAC) will be looking at: Will we all need a Covid-19 booster or will it be mandated only for certain groups? When might we need to boost our immune systems and how will this be decided? Would it be best to use the same brand of vaccine as a booster shot? Does the existence of variants mean modified versions of existing vaccines will be needed to offer ongoing protection against the novel virus?

One of the issues that has been addressed, in the context of a possible autumn booster campaign, is the co-administration of Covid-19 and influenza vaccines. Recently updated NIAC guidance says “Covid-19 vaccines and other vaccines may be administered at the same time or at any interval”.

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This means that a possible autumn Covid-19 booster campaign could be helpfully “piggy-backed” on to the annual flu shot as one single visit.

While there is caution about the possibility of variants 'breaking through' the defence of our vaccines, the most recent data on the Indian variant is reassuring.

But back to more basic considerations: will there be a need for a Covid-19 booster? The short answer is that nobody can be sure. Revaccination hinges on two factors: the prevalence of vaccine-resistant variants and the issue of waning immunity. Speaking to Pulse magazine, vaccine expert Dr Peter English said "there is 'minimal evidence' that people's immunity will have decreased by the autumn, even for those who were vaccinated earliest".

Dr Anthony Fauci, respected medical advisor to the US president Joe Biden, told a recent Senate committee hearing that coronavirus booster shots will probably be needed for vaccinated Americans: "I don't anticipate that the durability of the vaccine protection is going to be infinite – it's just not. So I imagine we will need, at some time, a booster. What we're figuring out right now is what that interval is going to be," he said.

While there is caution about the possibility of variants "breaking through" the defence of our vaccines, the most recent data on the Indian variant (B.1.6172) is reassuring. A study by Public Health England, published on May 22nd, found both the Pfizer and AstraZeneca vaccine offer high levels of protection against symptomatic disease from the Indian variant, following two doses. However, manufacturers Pfizer, Moderna and AstraZeneca are accelerating the development of tweaked boosters to combat the variants.

Autumn 2022

Will it be best for us to get the same brand of vaccine or a different type as a booster shot? The jury is out on this, with the European Medicines Agency (EMA) saying more data and evidence is needed to give a third dose – whether a booster dose of existing vaccines or one developed for variant strains.

There are lots of “known unknowns” when it comes to the why, when, where and what of booster Covid-19 vaccines. If readers will allow me a guesstimate, I predict the following: we will require boosters for Covid-19, probably on an annual basis. A booster campaign in the autumn of 2021 will be limited to priority groups, such as older people and those who are immunocompromised.

As for the rest of us, I predict the average person will not require a booster vaccine until autumn 2022.

mhouston@irishtimes.com, muirishouston.com