The CDC's recent shift in monitoring breakthrough COVID-19 infections after vaccination hasn't sat well with everyone, as some scientists are concerned it could miss the full picture of what is happening with these breakthrough cases.
As of May 1, the agency went from monitoring all breakthrough infections after COVID-19 vaccination to focusing on only hospitalized or fatal cases.
The rationale for this change is to focus on cases that are of "most importance to public health," and it is "not a resource limitation question," said Tom Clark, MD, MPH, deputy director of the division of viral diseases at the CDC and lead of the agency's vaccine evaluation team.
"We're focusing on breakthrough cases that have contact with the health system," he told MedPage Today.
Recent CDC data on breakthrough cases indicate that "the vaccines are working well," Clark added.
Data from the Morbidity and Mortality Weekly Report found out of 101 million fully vaccinated individuals, around 10,000 reported a breakthrough infection. Of specimens available for sequencing, 64% were variants of concern.
"The variants we identified in breakthrough cases looked very similar to the ones we identified in our strain surveillance nationwide. There were no red flags," Clark said. "What we're learning from vaccine effectiveness studies is that the vaccines are protecting well against strains that are circulating in the U.S."
Even though he characterized this data as "really reassuring," some scientists have been concerned that focusing only on more severe breakthrough cases could miss important information.
Missing the Full Picture
Understanding as much as we can about breakthrough cases is "essential," according to Michael Kinch, PhD, of Washington University in St. Louis, Missouri. Kinch has done research on drug discovery for cancer and infectious diseases.
"I'm not supportive of this change. I'd rather err on the side of having too much information," he told MedPage Today. "My worry is that missing variants could potentially evade the effectiveness of vaccines. When we find a variant like that, we want to try to snuff it out as quickly as we can."
Because the same viral strain may cause only mild illness in one person but deadly illness in another, not tracking mild breakthrough cases could risk missing out on the "full picture," of SARS-CoV-2 infection, he added.
Rick Bright, PhD, the former director of the Biomedical Advanced Research and Development Authority (BARDA), said in a May 24 interview with MarketWatch that we should learn from the lessons of influenza, for which the vaccine is only partially effective.
He added we should analyze SARS-CoV-2 in a "unique way" by looking at all the variants that are emerging, cataloging them, seeing how well they grow and spread, and seeing how well current vaccines work against them. Bright is currently senior vice president of pandemic preparedness at the Rockefeller Foundation.
Breakthrough infections in vaccinated individuals are "the most important viruses that we should look at," he said. "Those are where the virus variants are going to appear, where mutations might occur, and the viruses there are already escaping immunity. That is where I would focus."
Very Reasonable Approach
On the other hand, Lee Harrison, MD, of the University of Pittsburgh, said the CDC's approach is "very reasonable."
"You can argue that ideally CDC would study all breakthroughs. But from a practical and public health standpoint, a very reasonable approach is to focus on the most severe cases," he told MedPage Today via email.
"Even with highly efficacious vaccines -- around 95% for the mRNA vaccines -- we expect to see breakthroughs, most of which will be mild and not that clinically meaningful. So it makes sense to focus efforts on the most important and informative cases," Harrison said.
He added that the CDC's analysis of breakthrough infections is not being conducted in isolation, and that the CDC has multiple layers of COVID-19 surveillance that will provide a "pretty complete picture of what's going on and how to formulate future vaccines."
For example, the CDC recently ramped up whole genome sequencing efforts. Clark said whole genome sequencing surveillance will look for variants in both breakthrough and non-breakthrough cases across all severities of illness. In April, the White House also announced an additional $1 billion will be made available to expand genomic sequencing.
Clark said that a range of surveillance systems are in place, which include Sequencing for SARS-CoV-2 (SPHERES), a public-private collaboration of over 200 institutions that is focused on large-scale, rapid genomic sequencing of SARS-CoV-2; and the National SARS-CoV-2 Strain Surveillance System (NS3), which provides information on strains circulating nationally and how prevalent they are. The CDC also developed a national COVID-19 vaccine breakthrough REDCap database, where state health departments voluntarily report breakthrough cases.
"We have many systems in place to understand if certain variants cause more severe disease or transmit more readily," Clark said.
Additionally, the CDC is conducting several vaccine effectiveness studies that will be "critical" in determining the effectiveness of vaccines against variants, according to Clark. These studies include analysis of vaccine effectiveness in special populations, such as the immunocompromised and residents of long-term care facilities.
He added that the CDC is also setting up a population-based project to look at breakthrough infections, which will "identify all confirmed cases" and will be designed to compare cases in vaccinated and unvaccinated individuals. These studies should provide data on whether a certain variant is more likely to cause a breakthrough infection or whether certain patient risk factors may be involved, he explained.
"Many of our vaccine effectiveness studies include sequencing, and our population-based project around breakthrough cases has enhanced sequencing to look at whether certain variants are more prominently associated with vaccine breakthroughs compared to unvaccinated people," he said.
Taken together, these efforts should be enough to capture what's going on with breakthrough cases, according to Clark.
Still, Kinch hopes that we will keep past missteps in mind, and learn from them.
"It's really important to make sure that we don't take actions or inactions today that we might regret tomorrow," he said. "We're 18 months into this. Hopefully, we will avoid problems that might arise 18 months down the road."
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