The Start of the 2018–19 Flu Season in the United States

Flu activity in the United States was low in October 2018 and, though it rose slowly through November, remained low across most of the country by early December. This CDC report covers September 30 to December 1, 2018.

Where things stood

In the week ending December 1:

• The share of outpatient visits for influenza-like illness (ILI) — fever with a cough or sore throat and no other known cause — equaled the national baseline, and was at or slightly above the regional baseline in four of the 10 Department of Health and Human Services regions (Regions 4, 7, 8 and 9).
• Most jurisdictions had minimal or low ILI activity since September 30, but two had moderate and two had high activity.
• Deaths attributed to pneumonia and influenza were below the epidemic threshold, and the rate of flu hospitalizations was low.
• Five laboratory-confirmed, flu-associated deaths in children had been reported since September 30.
• Forty states, the District of Columbia, Puerto Rico and the U.S. Virgin Islands reported sporadic or local spread; nine states (California, Connecticut, Georgia, Kentucky, Louisiana, Nevada, New York, Oregon and Vermont) reported regional activity; and one, Massachusetts, reported widespread activity.

Percentage of outpatient visits for influenza-like illness, 2018–19 and selected earlier seasons, as of December 7, 2018. CDC.

Which viruses

Public health laboratories reported influenza A(H1N1)pdm09 most often: 67% of all viruses and 81% of subtyped influenza A viruses since September 30. A(H3N2) and influenza B viruses were circulating too.

Most viruses characterized were genetically and antigenically similar to the reference viruses behind the 2018–19 Northern Hemisphere vaccines, and none were resistant to oseltamivir, zanamivir or peramivir.

What to expect

Timing varies, but flu activity would rise in the following weeks and was likely to peak between December and February.

Vaccination. Everyone 6 months and older without contraindications should get a flu vaccine every year. Several vaccines were approved and recommended for 2018–19, and vaccination should continue as long as flu viruses circulate and unexpired vaccine is available. Manufacturers projected 163–168 million doses for the season; about 163.8 million had been distributed by November 30.

The season's trivalent vaccines contained an A/Michigan/45/2015 (H1N1)pdm09-like virus, an A/Singapore/INFIMH-16-0019/2016 (H3N2)-like virus and a B/Colorado/06/2017-like (Victoria lineage) virus; quadrivalent vaccines added a B/Phuket/3073/2013-like (Yamagata lineage) virus.

Antivirals are an important complement to vaccination. Four were recommended for treatment that season: oral oseltamivir, inhaled zanamivir, intravenous peramivir and the newly approved oral baloxavir. Treatment as soon as possible after illness begins is recommended for people with confirmed or suspected flu who are severely ill, have complicated or worsening illness, need hospitalization, or are at high risk of complications. Oseltamivir and zanamivir can be considered to prevent flu in certain situations, but routine seasonal or pre-exposure preventive use is not recommended.

Sources

Based on Budd AP, Abd Elal AI, Alabi N, et al., "Influenza Activity — United States, September 30–December 1, 2018," MMWR Vol. 67, No. 49, CDC; a work of the United States government in the public domain.