The 2026–2027 influenza season is under way, and the Centers for Disease Control and Prevention has opened its season pages with the usual toolkit: weekly surveillance reports, burden estimates, and prevention guidance last updated in September. In pharmacies and supermarkets, a parallel season is also opening — the annual run on products that promise to “support” or “boost” immunity.

The two conversations are not equally well documented. Here is what the public health guidance and the federal evidence reviews actually say.

The recommendation that comes first

The CDC is direct about priorities. “The single best way to reduce the risk of seasonal flu and its potentially serious complications is to get vaccinated each year,” its prevention guidance states, noting that seasonal vaccines are formulated to protect against the three influenza viruses research indicates will be most common in the coming season.

Everything else in the agency’s list is unglamorous and familiar: avoid close contact with people who are sick, stay home while you are sick, cover coughs and sneezes, wash your hands often, keep hands away from your eyes, nose and mouth, bring in fresh air or purify indoor air, and clean frequently touched surfaces such as countertops, handrails and doorknobs.

The CDC adds general health habits to that list — plenty of sleep, regular physical activity, stress management, fluids and nutritious food. On the hydration and rest side, our own guides to drinking enough water and to evening routines and sleep cover the same ground. The agency frames these as supporting habits, not as substitutes for vaccination.

It also sets a return-to-normal marker for anyone recovering from a respiratory illness: at least 24 hours in which symptoms are improving overall and there has been no fever without the use of fever-reducing medication.

What the supplement aisle looks like under review

The National Center for Complementary and Integrative Health, the NIH center that evaluates complementary approaches, states its flu conclusion without hedging: no complementary health approach has been shown to be helpful for the flu.

For colds, the center sorts the evidence into two piles. Approaches with some promise include oral zinc products, rinsing the nose and sinuses, honey as a nighttime cough remedy for children, vitamin C in people under short periods of extreme physical stress, probiotics and meditation. Approaches whose evidence is conflicting, inadequate or mostly negative include vitamin C for most people, echinacea, garlic and American ginseng.

Some of the specific reviews behind those labels are worth spelling out, because they are narrower than the marketing:

  • Vitamin C. A pooled analysis of 29 studies involving more than 11,000 people found that vitamin C does not prevent colds in the general population and shortens them only slightly. Started after symptoms appear, it made no difference to length or severity. The exception was people under brief, extreme physical stress — marathon runners and skiers — among whom it roughly halved the number of colds.
  • Echinacea. More than 24 studies have tested it, and a comprehensive 2014 assessment concluded it had not been convincingly shown to be beneficial, though some products might have a weak effect. The center notes that echinacea products vary so much in species, plant part and manufacture that findings for one may not apply to another.
  • Oral zinc. A 2012 evaluation of 17 studies found that zinc lozenges, tablets or syrup can reduce how long colds last in adults. Bad taste and nausea were reported by some participants.

Three cautions that get less airtime than the claims

The same NCCIH review flags risks that rarely appear on the front of a package:

  • Zinc products used inside the nose — gels and swabs — have been linked to long-lasting or permanent loss of the sense of smell. The FDA warned consumers about this in 2009, and the center’s position is that the risk of a serious, lasting side effect outweighs any possible benefit for a minor illness.
  • Nasal rinsing devices such as neti pots are not safely used with untreated tap water. In 2011 a severe amoebic infection was linked to tap-water rinsing; the FDA advises using water that has been filtered, treated or processed in specific ways, and cleaning the device as directed.
  • Honey should never be given to infants under 1 year old, because it may carry the spores that cause infant botulism. For older children it is considered safe.

What we did not find

Several things that are widely assumed did not turn up in the guidance. There is no complementary approach the NIH center says has been shown to prevent flu or relieve its symptoms. There is no product that prevents colds in the general adult population. There is no vaccine for the common cold, which MedlinePlus notes can be caused by more than 200 different viruses, with rhinoviruses the most common type. And antibiotics do not help with colds, because they treat bacterial infections rather than viral ones.

Two practical facts from MedlinePlus are also worth keeping in proportion: adults average two to three colds a year, and most people feel better within a week or two.

Where antivirals are concerned, the NCCIH review is explicit that prescription flu drugs are a second line, used in people who are very ill or at high risk of complications, that they work best started early, and that they are not a substitute for vaccination.

None of this is a diagnosis or a treatment plan for any individual. Readers weighing vaccination, an antiviral prescription or a supplement — and especially anyone who is pregnant, managing a chronic condition, or considering a product for a child — should raise the question with a healthcare professional, in line with our medical disclaimer.