Anecdotes tell us what the data can’t: Vaccinated people appear to be
getting the coronavirus at a surprisingly high rate. But exactly how
often isn’t clear, nor is it certain how likely they are to spread the
virus to others. And now, there’s growing concern that vaccinated people
may be more vulnerable to serious illness than previously thought.
There’s
a dearth of scientific studies with concrete answers, leaving public
policy makers and corporate executives to formulate plans based on
fragmented information. While some are renewing mask mandates or delaying office reopenings, others cite the lack of clarity to justify staying the course . It can all feel like a mess.
“We have to be humble about what we do know and what we don’t
know,” said Tom Frieden, a former director of the Centers for Disease
Control and Prevention and the head of the nonprofit Resolve to Save
Lives. “There are a few things we can say definitively. One is that this
is a hard question to address.”
Absent clear public health messaging, vaccinated people are left
confused about how to protect themselves. Just how vulnerable they are
is a key variable not just for public health officials trying to figure
out, say, when booster shots might be needed, but also to inform
decisions about whether to roll back reopenings amid a new wave
of the virus. On a smaller scale, the unknowns have left music lovers
unsure if it’s OK to see a concert and prompted a fresh round of
hang-wringing among parents pondering what school is going to look
like.
In lieu of answers, what has emerged is a host of case studies
providing somewhat different pictures of breakthrough infections.
Variables including when the surveys were conducted, whether the delta
variant was present, how much of the population was vaccinated and even
what the weather was like at the time make it hard to compare results
and suss out patterns. It’s difficult to know which data might
ultimately carry more heft.
“It’s quite clear that we have more
breakthroughs now,” said Monica Gandhi, an infectious disease expert at
the University of California, San Francisco. “We all know someone who
has had one. But we don’t have great clinical data.”
One of the best known outbreaks among vaccinated people occurred in the
small beach town of Provincetown, Massachusetts, as thousands of
vaccinated and unvaccinated alike gathered on dance floors and at house
parties over the Fourth of July weekend to celebrate the holiday -- and
what seemed like a turning point in the pandemic. About three-fourths of
the 469 infections were among vaccinated people.
Authors of a CDC case study said
this might mean that they were just as likely to transmit Covid-19 as
the unvaccinated. Even so, they cautioned, as more people are
vaccinated, it’s natural that they would also account for a larger share
of Covid-19 infections and this one study was not sufficient to draw
any conclusions. The incident prompted the CDC to reverse a
recommendation it had issued just a few weeks earlier and once again
urge the vaccinated to mask up in certain settings.
Still, the particular details of that cluster of cases may have made that outbreak especially bad, according to Gandhi.
“The rate of mild symptomatic outbreaks in this population was higher
because of a lot of indoor activity (including intimacy), rain that
weekend, not much outside time and mixture of people with different
vaccination status,” she said in an email.
A newly released, far larger CDC case study
of infections in New York state, meanwhile, found that the number of
breakthrough infections has steadily ticked up since May, accounting for
almost 4% of cases by mid-July. Those researchers cautioned that
factors such as easing public health restrictions and the rise of the
highly contagious delta variant might impact the results.
Yet another CDC case study, in Colorado, found that the
breakthrough infection rate in one county, Mesa, was significantly
higher than the rest of the state, at 7% versus about 5%. The report
suggested it was perhaps because the delta variant was circulating more
widely there, but also noted the ages of patients in Mesa and the lower
vaccination rate may have played a role.
Research
out of Israel seems to back the idea that protection from severe
disease wanes in the months after inoculation, and more recently, that
breakthrough cases may eventually lead to an uptick in hospitalizations.
The information is preliminary and severe breakthrough cases are still
rare, but it bolsters the case that some people will need booster shots
in coming months.
Case studies and data from some states in the U.S. have similarly shown
an increase in breakthrough cases over time. But with the delta variant
also on the rise, it’s difficult to tell whether waning immunity to any
type of coronavirus infection is to blame, or if the vaccinations are
particularly ineffective against the delta variant. It could be both, of
course. Changing behavior among vaccinated people could be a factor, too, as they return to social gatherings and travel and dining indoors.
All that said, some facts are well established at this point.
Vaccinated people infected with the virus are much less likely to need
to go to the hospital, much less likely to need intubation and much less
likely to die from the illness. There’s no doubt that vaccines provide
significant protection. But a large proportion of the nation -- almost
30% of U.S. adults -- have not been vaccinated, a fact that has
conspired with the highly contagious delta variant to push the country
into a new wave of outbreaks.
“The big picture here is that the
vaccines are working and the reason for the spike in the U.S. is we have
too little vaccine uptake,” Frieden said.
To a certain extent,
breakthrough cases of any virus are expected. In clinical trials, no
Covid vaccine was 100% effective -- even the best vaccines never are.
The more the virus is in circulation, the greater the risk of
breakthrough cases. It’s also common for some aspects of viral immunity
to naturally wane over time.
For the time being, there are simply more questions than answers. Are
breakthrough infections ticking up because of the delta variant, waning
immunity or a return to normal life? Are vaccinated people more
vulnerable to severe illness than previously thought? Just how common
are breakthrough infections? It’s anyone’s guess.
“It is generally
the case that we have to make public health decisions based on
imperfect data,” Frieden said. “But there is just a lot we don’t know.”
https://www.bloomberg.com/news/articles/2021-08-20/delta-case-wave-in-u-s-northeast-may-be-nearing-its-peak
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