How the US actually tracks Covid-19 now: the surveillance systems and the 2026-2027 vaccine formula

The United States no longer counts Covid-19 cases in any meaningful national way. The daily case dashboards that defined 2020 and 2021 are gone, and what replaced them is less intuitive but more durable: a set of indirect indicators that infer how much virus is circulating without needing anyone to take a test and report it. Anyone trying to answer the simple question of whether Covid is going around right now is, in practice, reading the output of three or four separate federal surveillance systems that measure different things on different schedules.

As of July 17, 2026, those systems agree that activity is low. The Centers for Disease Control and Prevention describes the overall amount of acute respiratory illness sending people to health care as very low, with Covid-19 activity very low and stable nationally — but with early signs of an increase, mainly in the South.

The direction of travel is the part worth watching, and it is genuinely mixed rather than settled. The picture is a national average sitting on top of considerable state-level divergence, and CDC's own framing pairs the reassuring headline with an explicit caveat about what could change it.

The reproduction number, and what 18 states means

CDC's Center for Forecasting and Outbreak Analytics publishes an estimate of Rt, the time-varying reproductive number — a measure of community transmission. An Rt above 1 means each infected person is on average causing more than one new infection, so infections are growing; below 1 means they are declining. Crucially, the agency does not estimate this from case reports. For this purpose Rt is estimated from daily incident emergency department visits reported through the National Syndromic Surveillance Program.

In CDC's Epidemic Trends dataset for July 14, 2026, the most recent modeling date available, 51 jurisdictions are scored. Ten are categorized as Growing and eight as Likely Growing — the 18 states CDC describes as growing or likely growing. Two are Declining and one Likely Declining, for three in retreat. Twenty-eight are Not Changing, and two are not estimated.

The named states behind that count are what make CDC's regional characterization concrete. The growing group includes Alabama, Florida, Louisiana, Mississippi, Oklahoma and Texas across the South, and Arizona, California, Nevada, New Mexico, Utah, Oregon, Alaska and Hawaii across the West. The declining group is small and geographically unrelated: New York, South Dakota and the District of Columbia. This is a summer pattern concentrated in the regions that had a quiet winter, which is consistent with CDC scenario modeling indicating that regions without substantial Covid-19 activity in the most recent winter months — the South and West — are expected to see increases in the summer.

Sewage, and why it exists

The second pillar is the National Wastewater Surveillance System, which CDC launched in September 2020 to coordinate wastewater surveillance run by state, tribal, local and territorial health departments. It now operates in all 50 states, three territories and five tribal organizations. Samples are collected at treatment plants, tested for SARS-CoV-2 at environmental or public health laboratories, submitted to CDC through the DCIPHER portal, analyzed, and published. Results are updated every Friday with the previous week's data, and each state is assigned a viral activity level of very low, low, moderate, high or very high.

The appeal of wastewater is that it does not depend on human behavior. It captures people who never test, test at home, or have no symptoms at all, which is why CDC credits it with detecting changes in disease trends before those trends appear in clinical data. That early-warning property is precisely what a system built on emergency department visits lacks, since a hospital visit is by definition a late signal.

The vaccine is re-chosen every spring

The other half of the federal apparatus is strain selection, which runs on an annual cycle closer to influenza than to the original pandemic vaccine rollout. FDA's Vaccines and Related Biological Products Advisory Committee met on May 28, 2026 to recommend the 2026-2027 formula.

The committee recommended that the composition of the COVID-19 vaccines (2026-2027 Formula) include the JN.1-lineage XFG as the preferred SARS CoV-2 virus variant for an updated monovalent vaccine.

FDA states the committee reviewed data on variant circulation, current vaccine effectiveness, human immunogenicity against recently circulating variants, antigenic characterization, and animal immunogenicity for candidate vaccines with updated spike components. On that basis the agency advised manufacturers that the 2026-2027 vaccines should be a monovalent JN.1 lineage XFG variant vaccine, in order to more closely match currently circulating SARS-CoV-2 viruses. That is a change from the 2025-2026 formula, which was a monovalent JN.1-lineage vaccine preferentially using the LP.8.1 strain. Both sit within the same JN.1 family; the update tracks drift inside that lineage rather than a jump to a new one.

What the low numbers do and do not rule out

The honest reading of July 2026 is that Covid-19 has become one seasonal respiratory virus tracked among several, and not currently the most active one. CDC reports influenza activity as low and RSV very low in most of the country, while parainfluenza is elevated nationally and rhinovirus/enterovirus is elevated in some regions. A summer respiratory illness is now more likely to be something other than Covid.

But CDC pairs its own observation of declining Covid-19 hospitalizations nationally over time with a specific conditional: it remains possible that there could be larger increases this summer, particularly if a variant that the immune system no longer recognizes becomes more common. That single sentence explains why the surveillance architecture survived the end of case counting. The systems are not there to produce a number for its own sake. They exist to detect the moment the trend line stops behaving, which is also the moment the annual strain-selection cycle would need to respond.

Details verified against CDC and FDA sources in July 2026. CDC's Epidemic Trends figures are drawn from the agency's public Rt dataset as of the July 14, 2026 modeling date and are revised as new data arrive; activity levels update weekly. Check the linked CDC and FDA pages for current figures before relying on them.