Delta variant ‘breakthrough infections’ guide

The infectious Delta variant has led to a substantial rise in “breakthrough infections” of Covid-19 among people who have been vaccinated. But the infections are mild or asymptomatic in more than 90% of cases, and Covid-19 vaccines are preventing hospitalisation and death in nearly everyone who has one.

The Sunday Times asked a range of experts to answer common questions about breakthrough infections...

What are breakthrough infections?

BTIs are Covid-19 infections that occur more than four weeks after getting vaccinated. Anyone who is fully vaccinated and develops Covid-19 is considered to have a BTI.

Why get vaccinated if I can still get Covid-19?

A Covid-19 vaccine is almost guaranteed to save your life even if you get infected, numerous studies and real-world observations show.

“They keep away the worst effects of the virus: severe illness, death and long Covid,” said Wits professor of medicine Francois Venter.

UCT infectious diseases expert, Professor Marc Mendelson, shared on Twitter: “I have yet to see a Covid-19 vaccinated person with Covid pneumonia in my high-care ward or one needing intubation and ICU. No vaccine is 100% effective so there will be the odd few, but you do the maths.”

Did vaccinations protect health-care workers in SA who got jabs under the Sisonke implementation study?

Yes. “Consistently we are finding that 94% of BTIs are mild, 4% are moderate and only 2% severe,” according to a Sisonke report on July 1.

Will I get symptoms with a BTI?

Some people do, but they are likely to be mild or moderate. Venter said: “Many of us think BTIs will become routine, like the common cold, and we are seeing it already in lots of people with J&J and Pfizer [vaccines]. The vaccine keeps you out of hospital in the vast majority of cases, it doesn’t make you totally immune to infection.”

A study among US health-care workers published last week shows that mRNA vaccines (Pfizer-BioNTech and Moderna) reduce the severity of Covid-19 symptoms, including fever and the length of illness, in breakthrough infections.

How much protection do the vaccines offer older people?

Glenda Gray, president of the South African Medical Research Council, said a US effectiveness study among vaccinated 65-year-olds found:

• The J&J vaccine prevented 11,800 hospitalisations, 3,300 ICU admissions and 2,300 deaths;
• mRNA vaccines prevented 12,500 hospitalisations, 3,500 ICU admissions and 2,400 deaths; and
• There were seven cases (J&J) and eight cases (mRNA vaccines) of severe side effects including blood clots and Guillain-Barré syndrome. These results were presented by the Centres for Disease Control (CDC) at a meeting on July 22, said Gray.

If I get a breakthrough infection, can I give Covid to other people?

Yes. The risk of infecting those around you is roughly halved but a CDC report on Friday suggests vaccinated people can pass on the Delta variant of the virus as easily as those who have not been inoculated.

Why do some people get BTIs and others do not?

Every person’s individual immune response determines how effectively they make neutralising antibodies to block the virus. A study at an Israeli medical centre found that people who make high levels of these potent antibodies have a lower risk of infection. Only 39 of the 11,500 got BTIs.

How long do the symptoms last?

Eight (19%) of the 39 Israeli healthcare workers who had BTIs still had some symptoms six weeks after infection. All those infected had mild symptoms or no symptoms.

Does the Delta variant mean I am more likely to get a BTI?

Yes. The Delta variant, dominant in SA and many countries, has massively increased the risk of breakthrough infections and they are much more frequent than expected.

Gray said: “There are BTIs everywhere. SA is no different.”

The Covid-19 vaccines being used in SA — J&J and Pfizer-BioNTech — remain effective against the Delta variant, but their potency is reduced.

Do health-care workers need a booster shot against Delta?

“We should give this serious consideration once SA is satisfied with the number of people who have got their first jab. Health-care workers are at high risk and deserve a booster dose before anyone else,” said Gray.

“The vaccine is effective but not 100% and this could close the gap. But there is not data or evidence for this.”