When Does Hand, Foot, and Mouth Disease Peak?

Hand, foot, and mouth disease (HFMD) typically peaks in late spring and early summer in temperate climates, with most countries reporting their highest case counts sometime between April and July. But where you live matters a lot: subtropical and tropical regions often experience a second, smaller wave in autumn, and in some equatorial areas the pattern becomes hard to pin down at all. The seasonality is driven by a mix of weather, school calendars, and the biology of the enteroviruses responsible, and each of those threads is worth pulling apart.

The Basic Pattern in Temperate Climates

If you live in a place with clearly defined seasons, HFMD follows a fairly predictable rhythm. Case counts start climbing in spring, peak sometime around June, and trail off as summer winds down. A systematic review covering studies from multiple continents found that most countries reported a single peak per year, most commonly in early summer.¹ In temperate parts of Asia, this summer peak has been documented repeatedly. Japan, for instance, shows a clear summer surge, and northern Chinese provinces like Beijing and Tianjin follow the same script with an annual peak in June.²

This single-peak pattern is what most parents in the United States, Europe, Japan, and northern China can expect. Pediatricians in these regions see the bulk of their HFMD cases between about May and July, with scattered cases year-round but nothing approaching the spring-summer concentration.

Two Peaks a Year in Warmer Regions

Move toward the subtropics and tropics, and the picture splits. Southern China reliably produces two waves of HFMD each year: a larger one peaking around May and a smaller one in September or October.³ Nationwide Chinese surveillance data from 2011 to 2018 confirmed this bimodal pattern, with the first peak running April through July and the second from September through November.⁴ The spring peak was consistently the larger of the two.

A systematic review of Asian data found the same split: temperate Asia had one summer peak, subtropical Asia had spring and fall peaks, and tropical Asia showed less clear seasonality altogether.⁵ Malaysia illustrates how messy things get near the equator. All Malaysian states showed a peak somewhere between weeks 25 and 35 of the year (roughly June through August), but the eastern states of Borneo also had an earlier peak between weeks 5 and 15 (February through April). And the year-to-year pattern within individual states was inconsistent, suggesting that in truly tropical areas, HFMD epidemic timing is less about a fixed seasonal rhythm and more about local conditions in a given year.⁶

The latitude gradient in China tells the story neatly. The further south a province sits, the stronger its second autumn peak becomes and the earlier its spring peak arrives. Northeast China, the coldest region, gets only one peak, and it comes in June. Central and southern regions see their spring peaks earlier and also get the autumn encore.⁷

Why Temperature and Humidity Shape the Peaks

The enteroviruses behind HFMD, primarily enterovirus A71 (EV-A71) and coxsackievirus A16 (CV-A16) along with several others, are sensitive to environmental conditions. Temperature appears to be the single most important weather variable. Modeling studies that compared the explanatory power of different factors consistently found temperature at the top of the list, ahead of humidity and other meteorological variables.⁸

Humidity runs a close second. Higher relative humidity appears to help enteroviruses survive longer outside the body, which makes sense when you consider how the disease spreads: through contact with fluid from blisters, saliva, nasal secretions, and fecal matter. Surfaces stay wet longer in humid air, and virus particles on those surfaces remain viable longer. Lab studies have shown that enteroviruses survive somewhat better at around 80% humidity compared with 60%.⁹ Research in Guangzhou also confirmed that rainfall and humidity tracked closely with HFMD incidence, and that water may serve as a reservoir for the viruses, reinforcing the role of wet conditions.¹⁰

A study in Ningbo, China, found that daily mean temperature, humidity, barometric pressure, and wind speed all showed statistically significant correlations with HFMD incidence, with the strongest predictive signal appearing about 19 days before case counts changed.¹¹ That roughly two-to-three-week lag fits what you’d expect: the weather changes, virus survival shifts, transmission ramps up, incubation plays out, and then cases show up at clinics.

Sunshine and ultraviolet light add another layer. A study in Yangzhou found that the risk of HFMD roughly doubled at peak sunshine durations compared with median levels, with the strongest effect at about a two-week lag.¹² Hong Kong data showed a similar relationship, with higher solar radiation linked to more cases.¹³ This might seem counterintuitive, since UV light is generally antiviral. But more sunshine means more outdoor play, more skin-to-skin contact between children, and warmer surfaces, all of which help the virus spread between people even if UV does reduce its environmental survival. A case-control study in Beijing actually found that UV radiation in indoor environments was protective, reducing outbreak intensity, while higher temperature was a risk factor.¹⁴ The distinction matters: UV directly hitting contaminated surfaces kills virus, but sunny weather driving children outside to play together spreads it.

The Role of School Calendars

Weather alone doesn’t fully explain HFMD peaks. The school calendar plays a meaningful supporting role, because the disease spreads fastest where young children are in close contact with each other for hours at a time: daycare centers, preschools, and kindergartens.

A modeling study in Singapore estimated that weekly case counts dropped to about 93% of normal levels during school vacations for children under 12. The effect was strongest in the 6-to-11 age group, where cases dropped to about 90% of non-holiday levels.¹⁵ School closures during autumn were particularly effective at curbing transmission, and a study across Chinese cities found that the impact of closures was even greater in less urbanized areas, where children’s social contacts are more concentrated in the school setting. In highly urbanized areas, children mix in many other settings, diluting the effect.¹⁶

Hong Kong presents an interesting counterpoint. Researchers there found that school holidays did not substantially reduce HFMD transmission. They noted that Hong Kong’s school breaks are relatively short outside of summer, and that transmission was often already declining before holidays began. Household transmission, which can be intense (sibling-to-sibling spread was estimated at very high rates), continues regardless of whether school is in session. And public playgrounds, which children visit more during holidays, can themselves be a transmission risk.¹⁷

So the school effect is real but modest, and it interacts with the local context. In places where childcare happens primarily in institutional settings, the school calendar shapes the peak. Where children mix in many other environments, closing schools barely dents the curve.

Different Viruses, Different Rhythms

HFMD is not caused by a single virus. Several enteroviruses produce the same clinical picture, and they don’t all behave identically in terms of timing. The two historically dominant culprits, EV-A71 and CV-A16, have different cycling patterns. Japanese surveillance data spanning more than three decades showed that CV-A16 follows a fairly clean annual cycle, peaking every summer. EV-A71, by contrast, has an underlying three-year periodicity layered on top of its annual fluctuations, meaning that EV-A71-heavy outbreaks tend to be larger every third year or so.¹⁸

Surveillance data from Zhengzhou, China, confirmed that all the major HFMD-causing serotypes showed roughly annual periodicity, cycling on about a 51-week pattern. But the strength of that annual signal varied by serotype, with EV-A71 showing the most dominant periodicity.¹⁹

Genetic analysis of EV-A71 has revealed that new subgenogroups can circulate quietly in human populations for up to five years before triggering a large outbreak. Rises in the virus’s genetic diversity tend to correlate with the onset of epidemics, suggesting that the emergence of novel viral lineages can amplify what would otherwise be a routine seasonal wave into something bigger.²⁰ This helps explain why some years produce devastating outbreaks while others, with similar weather, stay relatively quiet.

The practical upshot for parents: HFMD season arrives at roughly the same time every year, but how bad it gets in any given year is partly a dice roll driven by which viral strains happen to be circulating and how much immunity the local child population has built up from past exposures.

How Higher Transmission Intensity Shifts the Timeline

An underappreciated finding is that higher overall transmission in a region doesn’t just produce more cases; it also shifts when the seasonal wave starts. Analysis of Chinese provincial data showed that provinces with higher HFMD transmission rates saw their annual peak begin earlier in the year, and those same provinces tended to have a higher proportion of cases among the youngest children (under two years old), with proportionally fewer cases in the three-to-five age group.²¹ In other words, where the virus circulates more freely, it finds susceptible children faster and the epidemic takes off sooner.

This means that two neighboring provinces can have meaningfully different peak weeks depending on population density, childcare practices, and baseline hygiene conditions. Parents in densely populated southern Chinese cities may see HFMD start appearing in March, while families a few hundred miles north might not see it until May.

How Vaccination Is Changing the Pattern

China licensed an inactivated EV-A71 vaccine in 2016, and its rollout has visibly reshaped the HFMD landscape. In one studied region, overall HFMD incidence dropped from about 215 per 100,000 in the pre-vaccination period to about 180 per 100,000 afterward.²² Shanghai’s experience has been more dramatic: incidence fell by roughly 57%, case severity dropped by about 95%, and fatalities from EV-A71 were eliminated entirely in the post-vaccination era.²³

But vaccination against one serotype creates ecological room for others. Since EV-A71 vaccination began, the dominant circulating viruses have shifted. CV-A6 and CV-A10, which were minor players before, have become the leading causes of HFMD in many vaccinated regions.²³ The age profile of cases has also shifted upward, with the proportion of cases in the 6-to-10 age group more than doubling. This likely reflects that younger children, who are the primary vaccine recipients, are now protected against EV-A71 while older, unvaccinated children remain susceptible to the serotypes the vaccine doesn’t cover.

For the timing question, vaccination hasn’t eliminated the seasonal pattern, but it has made the peaks somewhat less predictable. The same post-vaccination surveillance found inconsistent seasonality from year to year, with some years producing one peak and others producing two.²² As serotype replacement continues and vaccine coverage expands, the familiar spring-summer surge may become less regular than it once was.

Surveillance Gaps and What Gets Missed

One reason HFMD’s seasonal pattern looks cleaner in some datasets than others is that surveillance systems have significant limitations. In South Korea, for instance, HFMD monitoring relies on designated sentinel sites that are meant to represent the national burden, but they don’t capture every case. Diagnosis is made purely on clinical symptoms without routine lab confirmation, so the causative serotype is often unknown. And mild or asymptomatic cases, which are common with enteroviruses, frequently go unreported because parents never seek medical care for a child with a few blisters and a low fever.²⁴

This means that the “peak” we observe in surveillance data is really the peak of medically attended cases, which skews toward more symptomatic infections. The actual peak of all infections, including mild ones that stay home, could be broader and shifted slightly earlier, since it takes days between when a child catches the virus and when a parent decides to visit a doctor. In countries without mandatory HFMD reporting, the seasonal curve might look different altogether if every infection could be counted. This is worth keeping in mind when you see precise peak-week estimates: they reflect the healthcare-seeking behavior of a specific population as much as they reflect the true biology of the virus.

Practical Timing for Parents Outside Asia

Most of the large-scale HFMD surveillance data comes from East and Southeast Asia, where reporting systems are more developed for this disease. But the same viruses circulate worldwide, and the seasonal logic holds. In the United States, the CDC has historically observed HFMD peaking in summer and early fall, consistent with the temperate-climate pattern seen elsewhere. European data follows a similar trajectory. Australia, being in the Southern Hemisphere, sees its peak shifted by six months, with cases climbing in their spring and summer (roughly October through February).

For parents, the actionable part is straightforward. If your child is in daycare or preschool, peak risk runs from roughly late spring through midsummer in temperate regions. In warmer climates, stay alert for a second wave in autumn as well. The two-to-three-week lag between weather changes and case increases gives you a useful early-warning window: when temperatures rise and humidity climbs, the clock is ticking. Emphasizing hand hygiene and surface cleaning during those months won’t eliminate risk, but it targets the right window. And if your region offers EV-A71 vaccination, it protects against the serotype most likely to cause severe complications, even though it won’t prevent all HFMD cases from other viral strains.