The Centers for Disease Control and Prevention released a guide Friday to safe classrooms in the era of COVID-19 as President Joe Biden pushes to maintain a campaign promise to reopen schools in his first 100 days. 

Most outbreaks in schools are due to lax mask-wearing, CDC Director Rochelle Walensky told reporters.

The road map centers on five mitigation strategies: universal and correct use of masks; physical distancing; hand-washing and respiratory etiquette; cleaning and maintaining healthy facilities; and contact tracing in combination with isolation and quarantine.

The road map emphasizes being mindful of rates of community spread. Just 5 percent of counties have low enough community transmission to justify reopening to all students full time.

Walensky emphasized that the CDC, which is not a regulatory agency, is not requiring that schools reopen.

The guidelines could reassure school administrators seeking safety in an ongoing pandemic and a simmering mental health crisis. Remote learning has set back academic achievement and emotional growth, cut off free and reduced meals in some areas, and trapped some children in dysfunctional homes. 

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But it’s not clear how many schools will reevaluate plans already in place. A majority of schools are already open in some capacity.

About half of school districts nationwide are offering a mix of in-person learning and online learning, according to reopening plans compiled and analyzed on Feb. 1 by MCH Strategic Data, which specializes in educational data. Another 18 percent of schools are offering full-time in-person learning to all students. Just 23 percent of districts are offering only online learning. 

Masking within schools is already common. An estimated 70 percent of school districts require students of all ages to wear masks. 

Still, some teachers and parents worry that the Biden administration’s messaging on schools does not take into account the challenges in stuffy, crowded classrooms found throughout the country.

The CDC road map recommends that schools open windows and doors when possible. Walensky said the CDC has recommended other strategies for improving ventilation, too, but it’s not clear how much funding different school systems would have for HVAC updates.

But about a third of public schools nationwide — roughly 36,000 schools — have outdated ventilation systems, according to government researchers. A 2020 Government Accountability Office report found that in 41 percent of U.S. school districts, at least half of the schools need repairs to HVAC systems. Even in schools where HVAC systems were updated, sometimes pipes and insulation serving the HVAC systems were not. 

According to the reopening plans compiled by MCH Strategic Data, 71 percent of schools have an isolated area for students who may be exhibiting symptoms. It’s not clear how many of those isolation rooms have their own HVAC systems, as the American Society of Heating, Refrigerating and Air-Conditioning Engineers advises.   

Affluent areas were more likely to have resources for renovations than high-poverty areas, the GAO report stated.

Anecdotally, parents and teachers have reported dramatic differences in infection control protocol between districts. In Philadelphia, for example, the school district reportedly installed makeshift ventilation systems pieced together from cheap window fans.

Ventilation concerns have been factors in delaying reopening in some urban school districts where the class sizes may be bigger and teachers unions have more sway.

Walensky said that while schools should conduct COVID-19 screening tests particularly for staff if possible, they are not a prerequisite for opening. Tests are not widely available for children in the United States, where tests are in high demand.

Biden is seeking $130 billion in funding for K-12 schools in a coronavirus relief bill making its way through Congress. Some Republican senators have bristled at that request. Some have said that schools received plenty of money through a March 2020 coronavirus relief law, which allocated $68 billion, or have proposed conditioning funding on reopening doors. 

The $130 billion would not be enough to cover all the estimated expenses, administration officials say. 

Although schools are notorious focal points for the spread of infectious diseases, COVID-19 is less likely to spread between children. Some outbreaks have occurred, but clusters are generally small, and there are fewer infections in schools doing hybrid learning than in the community, according to studies conducted in North Carolina and Washington state. 

But there are some limitations to the data. The CDC warned that it has been tough to track the number of cases among teachers and staff. The data also are not designed to reflect the increasing risk of transmission as worrisome viral variants gain ground in the United States. 

Walensky acknowledged that variants are a concern the CDC would continue to monitor. 

The CDC road map recommends that teachers be prioritized for vaccinations, but the agency has said mass vaccination should not be a prerequisite for reopening. 

Teacher vaccinations are spotty. A reordering of CDC priority guidelines has delayed teacher vaccinations in many states. Thirty-four states initially prioritized teachers in the 1B category according to CDC guidelines, which recommended vaccinating educators and other essential workers along with people age 75 or older, according to Johns Hopkins University.  

But a shortage of vaccines and the national expansion of eligibility to people who are 65 to 74 years old ahead of the CDC’s timeline ratcheted up competition for a vaccine. Many teachers in states like North Carolina were bumped from the line, while in states like California, teachers reportedly struggle to secure appointments.