The influenza virus gained an important ally during the last few weeks: the Trump administration. If you have been rooting for a widespread and virulent flu epidemic this winter, several of its new immigration policies should give you reason to cheer.

The first bit of good news for flu fans is a decision to withhold vaccination from children held in Customs and Border Protection detention centers. These facilities are supposed to hold migrants for no longer than three days, but many remain much longer, and the centers are often severely overcrowded. Since the flu can be quite serious, this puts the thousands of children held in them at increased risk of major illness or death.

Of course, that aspect of a Trump administration immigration policy is hardly news. At least three children have already died in detention centers of flu-related causes.

The real excitement for flu enthusiasts is that any residential facility where people live in close quarters is a perfect breeding ground for the virus. If any of the unimmunized children contract the disease, they can easily transmit it to workers, visitors, and anyone else with whom they come into contact. Those people, in turn, can spread the virus more widely outside the facility.

The policy coincides with another that permits immigrant families to be held indefinitely while awaiting decisions on their cases. There had been a 20-day limit on holding children. Conditions in detention facilities are often unsanitary and have reportedly led to flu outbreaks in the past. The new policy gives the virus better access to a large pool of people among whom it can incubate.

A final new policy that gives the flu a boost is the “public charge” rule for legal immigrants that is slated to go into effect this fall. That policy penalizes immigrants hoping for citizenship or a green card if they have used a safety-net program while they are waiting. Included among those programs is Medicaid, which covers health-care expenses for those who are poor or near poor. It is the only insurance that many people who are looking for work or are working in low-wage jobs can find or afford.

The rule means that legal immigrants who become ill while still finding their bearings in the country face the choice of forgoing health care or jeopardizing their shot at permanent legal status. With their dream of staying in the United States on the line, many will see health care as the disposable option. If their illness is an infectious disease like the flu, lack of treatment reduces the chance of stopping it quickly, which makes them more likely to spread it to others.

The rule could also discourage immigrants from seeking flu vaccines for themselves and their children. Even though it doesn’t apply to children’s use of Medicaid, the rule has already begun to exert a chilling effect, making parents fearful of accessing pediatric care. Increasing the number of unvaccinated people weakens the phenomenon of “herd immunity” through which entire communities can be protected against an infectious disease when enough of their members are immunized.

None of this necessarily means that the flu will have an easy time of it this year. Widespread vaccination among the general population or a weaker strain could still lead to a mild flu season. But the latest round of Trump administration immigration policies makes that possibility less likely.

Immigration is a complex issue, and new policies can have wide-ranging unanticipated effects. For those of us rooting against the flu, the possible effects of the new Trump administration policies deserve a lot more attention than they seem to have received. The health of everyone is at stake.

Robert I. Field is professor of law and public health at Drexel University.” He is also founder, editor, and lead writer of the Health Cents blog on Inquirer.com.