Covid-19: Don't wait until autumn for a booster vaccine

Covid-19 is no longer officially a global health emergency, but the World Health Organization (WHO) says SARS-CoV-2, the coronavirus that leads to Covid-19, is here to stay.

New booster shots designed to target Omicron subvariant XBB.1.5, which is currently the most dominant, are expected to become available by September or October — at the start of autumn in the Northern hemisphere.

But there are concerns that the existing vaccines will be ineffective against emerging strains like EG.5, also known as Eris.

When should I get my next COVID booster vaccine?

On 9 August 2023, the WHO classified EG.5 as a "virus of interest", one step below the more serious level of "virus of concern".

That risk evaluation for EG.5 seemed to have been the prompt for a New York Times article that suggested readers would be "a lot better off" if they waited "another month or two" to allow for an updated vaccine to be approved, instead of getting whichever boosters were available now.

Further into the article, however, their advice — based on interviews with three US-based infectious diseases and vaccine experts — appeared a little confusing.

First they say that "antibodies produced by the updated vaccine may not be quite as effective against [EG.5]". Then they say "the new booster is still a better fit for EG.5 than last year's booster".

So should you or shouldn't you get a booster vaccine is you are scheduled for one now?

Waiting to get a booster is 'silly advice'

The experts that DW contacted for this article challenged the advice in the NYT, arguing that any vaccine was better than none, especially if you are older than 65 years or have a condition that puts you at risk of serious Covid symptoms.

"This is silly advice," says Paul Hunter, an emerging infectious disease expert at the University of East Anglia, UK. "It's better to have the current vaccine than wait for an improved one."

Wait for a new vaccine, points out Hunter, and you increase the risk of serious Covid infection from a current or older variant.

"Every new variant that has appeared since Omicron hangs around for three months. If you wait a few months before getting a[n updated] vaccine that's good against EG.5, the variant will be history by the time the vaccine comes to market," Hunter says.

What is the best Covid vaccination strategy, then?

Covid is currently being managed by seasonal vaccination programmes.

"We don't have a long-lasting vaccine or a sterilising vaccine like we do for measles, therefore immunity doesn't last from year to year," says Keith Neal, an epidemiologist at the University of Nottingham, UK.

We therefore need to rebuild immunity for each new Covid variant through infection or booster shots. Vaccines can be changed very quickly to target the latest coronavirus strains, so they are always playing catch-up with new variants.

The difficulty with developing new shots is knowing which strains are likely to be the most dominant in the coming months.

"It's similar to the flu vaccine, where we make an informed guess — we say, 'Look, this variant has been circulating in Australia this winter, so we'll put that in our vaccine for the Northern Hemisphere's upcoming winter'," says Neal.

Neal says the best strategy is to get your Covid vaccine whenever you can, as soon as you're due.

"If things change substantially, we could give high-risk people a second Covid booster this winter. We always have strategies for situations that go worse than expected," he said.

Why vaccinate in autumn?

Respiratory virus infections, such as Covid-19 and influenza, tend to be more frequent in winter than in summer, and also tend to cause more severe diseases then.

Timing a booster campaign to early autumn gives the best protection during the worst time of the year for respiratory viruses.

"It means you can reduce Covid infections at a time when other respiratory infections are quite high, which takes pressure off health services. Getting both influenza and Covid at the same time isn't good," adds Hunter.

Vaccines don't necessarily reduce virus transmission from one person to another, Hunter reminds, but they do protect people against severe infections.

"It does this very well, especially in people with hybrid immunity — that is immunity from vaccination and a prior Covid-19 infection. This is why it's so important to get vaccinated," Hunter said.

Is there an alternative to seasonal Covid vaccines?

Moderna, a US-based pharmaceutical company, published early trial data on August 17 that suggested their new mRNA Covid vaccine targetted at the XBB strains was also effective against EG.5 and another emerging variant called FL1.5.1 or Fornax.

At time of writing, their updated vaccine was awaiting approval by the European Medicines Agency (EMA) and the US Food and Drug Administration (FDA).

While this is good news for booster programs in the short term, it does little to establish long-term sterilising immunity, and some worry that vaccine fatigue may hinder such long-term immunity.

So, scientists are working on what's called a pan-sarbecovirus vaccine — a vaccine that causes long-lasting and universal sterilizing immunity to SARS-CoV-2, much like the shot that helped eradicate smallpox.

"This wouldn't just work against SARS-CoV-2, but also against other beta coronaviruses, meaning it would be hugely beneficial against future potential pandemics," said Hunter.

Promising pan-sarbecovirus vaccine candidates are in the works, but huge development costs are hindering progress. The first candidates may come into clinical use in 2024.