Coronavirus: what we know about 'breakthrough' infections in vaccinated people

Breakthrough infections became news in India's recent surge, but scientists say only a tiny fraction of vaccinated people become very ill

Medical experts emphasised that Covid-19 vaccines are extremely effective and the only way to end the pandemic.

Several top scientists gave their views as breakthrough cases, when a vaccinated person becomes sick or even dies from coronavirus-related illness, were reported in the US and India.

The latest data adds to previous evidence that the vaccines, while not offering 100 per cent protection against Covid-19, significantly cut the risk of serious illness and death.

The publication of official figures show small numbers of vaccinated people have died globally, but they have been taken out of context and proportion.

“The vaccines are highly effective, remarkably effective, including the vector-based and mRNA [messenger RNA] ones,” said David Taylor, professor emeritus of pharmaceutical and public health policy at University College London.

“If something isn’t 100 per cent effective, it doesn’t mean it should be blamed for unfortunate individuals who don’t respond well.”

'Breakthrough' infection count

The US Centres for Disease Control and Prevention regularly releases figures for the US on breakthrough infections.

These are classed as affecting people who received a second vaccine dose at least two weeks earlier.

In its latest update, the CDC said it received reports of 9,245 breakthrough infections, in which 132 patients died.

With 20 of these deaths, the infection was asymptomatic or the person died from something other than Covid-19.

In contrast, more than 570,000 people in the US have died of Covid-19 or complications stemming from it.

“If it’s one in a million or two or three in a million, you’re looking at unusual biology,” Prof Taylor said.

“It’s probable that if the people were fully vaccinated and have been vaccinated for some time and they’ve fallen victim to the disease, they would’ve fallen victim anyway.”

India, in the middle of a huge infection surge, does not publish breakthrough infection death numbers.

But it estimated that between two and four people in every 10,000 vaccinated people are reinfected with the virus.

Last month, it recorded 180 "post-vaccination deaths", but that included deaths from potentially unrelated illnesses.

The figures were largely taken out of context on social media.

As of Saturday, 103.4 million people in the US had received two doses of a Covid-19 vaccine, suggesting that so far about one in a million fully vaccinated people have contracted Covid-19 and died.

In an online briefing document, the CDC emphasised that vaccine breakthrough cases “occur in only a small percentage of vaccinated persons”.

It recommends that fully vaccinated people continue to wear masks, maintain social distancing, wash their hands often and avoid crowds and poorly ventilated spaces.

Last week, the CDC released findings indicating that being fully vaccinated cut the risk of hospital admission by 94 per cent in people aged 65 or above.

Using data from two US healthcare networks with 24 hospitals in 14 states, a study found people who were partially vaccinated, meaning they had one dose of a vaccine at least two weeks earlier, were 64 per cent less likely to be need hospital treatment.

The CDC described the results, which related only to people vaccinated with the Pfizer-BioNTech or Moderna mRNA vaccines, as the first real-world findings in the US confirming the effectiveness of those types of vaccines at preventing serious illness.

The US authorised the use of a third coronavirus vaccine, from the Johnson & Johnson subsidiary Janssen.

Like the Oxford-AstraZeneca and Sputnik V vaccines, this is based on non-replicating adenoviruses that cannot cause infection.

Like the US, in other countries where large proportions of people have received shots, including Israel and the UK, death rates have dropped, although factors such as lockdowns have also been at play.

The UAE, which also has among the highest vaccination rates, had a gradual decline in deaths last month after they peaked in February.

Prof Taylor said a mix of measures would be required over the next two or three years to control the pandemic, including immunological control, which includes protection from vaccination, and epidemiological control, which takes in behavioural measures such as social distancing and mask-wearing.

“I think the key will be if we can get oral drugs that will control the disease early. That will be the big game-changer,” he said.

“Probably by the end of this year we’ll be looking at a situation where we’ve got drugs that can be used early and effectively on a mass scale.”

Updated: May 3, 2021 07:05 PM

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