In several weekly updates published today, the US Centers for Disease Control and Prevention (CDC) said seasonal influenza and RSV (respiratory syncytial virus) activity are low nationally, and COVID-19 activity is elevated but declining.

The test-positivity percentage for COVID-19 dropped to 11.6% last week from 13.4 % the prior week, according to the weekly update for the week ending on September 21.

Other COVID indicators declined as well, but only slightly. Emergency department visits dropped from 1.7% to 1.4%, and hospitalizations per 100,000 population dropped to 4.0, down from the prior week's 4.1. In its biweekly variant update, the CDC noted that the KP.3.1.1 Omicron subvariant accounts for 52.7% of infections, the same as 2 weeks ago.

Wastewater levels for COVID-19 remain high but low for RSV and influenza. Of flu cases identified through specimens testing, the H1N1 strain accounts for 53.5% of cases, H3N2 for 46.5%, and influenza B for 1.2%. Influenza test positivity for the week ending on September 21 was 0.6%.

Outpatient respiratory illness visits also remained steady, at 1.9%.

Of note, the CDC recorded no new human infections with novel influenza A viruses, with the season's total remaining at 23. 

Very low vaccine uptake

According to the CDC, the early weeks of flu vaccine availability have resulted in 9.6% adults reporting receipt of a flu vaccine and 4.5% of adults reporting receipt of the updated 2024-25 COVID-19 vaccine

Among adults 75 years and older, 34.0% reported ever receiving an RSV vaccine.

The World Health Organization (WHO) today announced the flu vaccine strain recommendations from its advisory group for the Southern Hemisphere's 2025 season. The WHO makes these recommendations twice yearly, once for each hemisphere, and they are used by the national vaccine regulatory agencies and pharmaceutical companies to develop flu vaccines for the following influenza season, the WHO said. 

"The periodic update of viruses contained in influenza vaccines is necessary for the vaccines to be effective due to the constant evolving nature of influenza viruses, including those circulating and infecting humans," the WHO said.

New H3N2 strain 

Mimicking last year's recommendation, the WHO recommends manufacturers produce trivalent (three-strain) vaccines for use in the 2025 Southern Hemisphere influenza season, given that one of the influenza B strains used in quadrivalent (four-strain) vaccines hasn't been detected in years. The 2009 H1N1 recommendations remain the same as last year's, as do the B/Victoria lineage recommendations, but the H3N2 component has changed.

For egg-based vaccines, the experts recommend an A/Victoria/4897/2022 (H1N1)pdm09-like virus; an A/Croatia/10136RV/2023 (H3N2)-like virus; and a B/Austria/1359417/2021 (B/Victoria lineage)-like virus. 

For cell-culture vaccines, they recommend an A/Wisconsin/67/2022 (H1N1)pdm09-like virus; an A/District of Columbia/27/2023 (H3N2)-like virus; and a B/Austria/1359417/2021 (B/Victoria lineage)-like virus.

For quadrivalent vaccines, the recommendation is unchanged from last year, a B/Phuket/3073/2013 (B/Yamagata lineage)-like virus.

The periodic update of viruses contained in influenza vaccines is necessary for the vaccines to be effective due to the constant evolving nature of influenza viruses.

The recommendations today do not deviate from the WHO's February recommendations for Northern Hemisphere flu vaccines. 

• In its weekly update today, the US Centers for Disease Control and Prevention (CDC) confirmed just 2 new measles cases, raising the national total to 264. The previous week saw 11 new cases. Among the case-patients, 88% were unvaccinated or their vaccine status was unknown, and 41% of the total were hospitalized. Seventy-three percent of patients were 19 years or younger, with 42% under age 5 years. The CDC has tracked 13 outbreaks that account for 70% of cases.
• Bavarian Nordic yesterday announced an agreement with UNICEF to supply 1 million doses of Jynneos mpox vaccine this year for African nations affected by mpox. UNICEF said the vaccine will be available at the lowest market price for 77 low- and lower-middle–income countries. The agreement includes the 500,000 doses that Gavi, the Vaccine Alliance, committed to earlier this month. Bavarian Nordic President and CEO Paul Chaplin, PhD, said the agreement "represents a significant contribution to the global efforts to combat the mpox outbreak in Africa." In related news, the Africa Centres for Disease Control and Prevention says it has received pledges of $814 million in support of mpox response efforts, a number that could top $1 billion, according to Reuters.
• The Global Polio Eradication Initiative yesterday in its weekly update noted 10 new polio cases in three countries: Pakistan, the Democratic Republic of the Congo (DRC), and Nigeria. Pakistan confirmed four cases of wild poliovirus type 1 (WPV1) in Balochistan, Sindh, and Khyber Pakhtunkhwa provinces, for 21 total WPV1 cases this year. That compares with 6 for all of last year. The DRC had 2 circulating vaccine-derived type 2 (cVDPV2) cases in Maindombe province, raising its 2024 total to 12. And Nigeria recorded 4 cVDPV2 cases in Borno, Gombe, and Yobe states, raising its total for the year to 57 cases.