Breakthrough cases – infections among vaccinated people – are happening. These are normal and expected because the vaccines, though all powerfully protective against Covid-19, are not 100% effective. But how many people, and which populations, are having breakthrough infections? And what are the chances they will develop long Covid, the cluster of debilitating symptoms that can last for weeks or even months?
It’s difficult to answer these questions because there’s a dearth of rigorous data on breakthrough cases in the United States. The US Centers for Disease Control and Prevention (CDC) tracks only breakthrough cases that lead to hospitalization and death, which it does by gathering data from state health departments. Only 25 states report some data on breakthroughs, and only 15 of those states update it regularly, according to a recent Kaiser Family Foundation analysis of state data. Encouragingly, this data suggests that breakthrough cases among the fully vaccinated are extremely rare – well below 1% in states collecting this information. (Note that undercounts are expected, since people with breakthrough infections may not know they are sick or bother to get tested.)
This is the kind of information that the public needs in order to understand the risks of daily life during the pandemic, and that scientists need to assess the shifting epidemiology of the virus. We should be able to rely on the CDC to collect and share this data. Instead, we are relying on nonprofits, media outlets and patient advocacy groups to fill the gap.
The CDC used to be more thorough in its surveillance of breakthrough cases. It tracked them all between 1 January and 30 April of this year, counting 10,262 in that time frame. But on 1 May, the agency changed its strategy to investigate only breakthrough cases that led to hospitalization or death. “This shift will help maximize the quality of the data collected on cases of greatest clinical and public health importance,” it explained.
There’s no question that learning about hospitalized or fatal breakthrough cases is critical. But it is just as important to know about the ones that don’t – the ones that are asymptomatic but still contagious, those that lead to mild symptoms and, crucially, those that develop into long Covid.
The general public must have this information so they understand how and why to protect themselves, even if they are vaccinated. Vaccine-hesitant people must have it so they can see that the likelihood of breakthroughs is rare because the vaccines are such a powerful shield against new infections. And researchers must have it so that they can understand how the virus is evolving and track any emerging vaccine-resistant variants that may be driving breakthrough cases.
A major concern regarding breakthrough cases is the possibility they may lead to long Covid. As I wrote recently for Slate, the limited data available suggest that this is possible even with mild or breakthrough cases, but the risk of this happening is unclear because, again: there’s hardly any data. Long Covid is a mysterious, devastating group of symptoms that may already be affecting millions of people, many of them young, making it impossible for them to return to work or resume normal life. It doesn’t necessarily lead to hospitalization or death, but the impact it has on quality of life is massive. Frankly, it is shocking that breakthrough cases that lead to long Covid are not counted among those of “greatest clinical and health importance” to the CDC.
Surveilling all breakthrough cases, regardless of outcome, would no doubt be an immensely resource-intensive endeavor for the CDC. But now is not the time to count costs – especially when it comes to gathering data that will be crucial to getting the coronavirus under control again. Early in the pandemic, we saw what happens when decisions are made without data. Covid tests were scarce and the data on infection rates scarcer, yet lockdowns were enforced, then lifted prematurely; hospitals overflowed because the timing of surges could not be predicted; and communication about the risk of infection and death faltered spectacularly.
Now, as the US case count has surpassed 35m, and more than 615,000 people have died, the highly contagious Delta variant is rising, cases are ballooning among the unvaccinated, and some vaccinated people are experiencing breakthroughs. There is much we do not understand. But what is clear is that we cannot afford to navigate yet another phase of the pandemic without data to guide our way.
Yasmin Tayag is a freelance science writer