Breakthrough Cases Hinder Fight

"LONDON -- Covid-19 infections among vaccinated people are complicating the fight to bring the coronavirus under control. And in the U.K., where the path of the disease has been more closely tracked than just about anywhere in the world, they are on the rise.

Breakthroughs happen because vaccines, while still offering strong protection against severe illness and death, aren't bulletproof. The virus can in some cases infect the body and replicate, causing illness, before the immune response can tackle it. Immunity also wanes over time, prompting many countries, including the U.K., to roll out booster-shot campaigns.

Breakthrough infections are expected to become more common as more people get vaccinated: if 100% of the population were vaccinated, every infection would be a breakthrough infection. However, U.K. data also suggest that among vaccinated people, the chances of getting a breakthrough infection are up.

The rise in breakthroughs in the U.K. is being driven in part by children, still largely unvaccinated in the U.K., passing on the virus to their vaccinated parents. A detailed study on household transmission in the U.K. suggests a vaccinated person who shares a home with somebody with symptomatic Covid-19 has a 25% chance of catching the virus.

 

In addition, breakthrough infections contribute to the spread of the virus, posing a risk to vulnerable and unvaccinated people. The household-transmission study also found that a vaccinated person with symptomatic Covid-19 is as likely to pass the virus to someone who shares their home as an unvaccinated one.

 

Also contributing to stubbornly high numbers in the U.K. are the tenaciousness of the fast-transmitting Delta variant and, some scientists say, the lack of social-distancing and other measures aimed at curbing transmission. Still, thanks to the vaccines, hospitalizations and deaths are a fraction of what they were in previous phases.

In most age groups in England, breakthrough infections are higher now than they were in mid-August, according to data from the U.K. Health Security Agency, formerly Public Health England. That rise has been especially stark in people in their 40s. In the four weeks to Oct. 31, 2.1% of fully vaccinated 40-to-49-year-olds tested positive for the virus. That is up around 90% from a four-week infection rate of 1.1% in mid-August. Other age groups have seen more modest increases -- between 22% and 56% -- in the rate of breakthrough infections. In under-30s, the rate is now lower than it was in mid-August.

Ajit Lalvani, chair of infectious diseases at Imperial College London and lead author of the household-transmission study, said people in their 40s were at higher risk of breakthrough infection for two reasons. "Waning immunity plus pools of unvaccinated people acting as vectors of infection into the household where it transmits effectively to vaccinated parents," he said. "Both are happening."

Most people in their 40s received their second vaccination at least four months ago. A recent study from UKHSA found that vaccine effectiveness started to wane as early as 10 weeks after the second dose for the vaccines developed both by Pfizer Inc. and BioNTech SE, and by AstraZeneca PLC and the University of Oxford, the two most common in Britain.

They are also the most-likely age band to share a home with teenage children, a group that is still mostly unvaccinated in the U.K. and in which case numbers have been surging." [1]

1. World News: Breakthrough Cases Hinder Fight
Roland, Denise.  Wall Street Journal, Eastern edition; New York, N.Y. [New York, N.Y]. 08 Nov 2021: A.18.