Quick takes: Louisiana pertussis rise, yellow fever in Ecuador, polio cases in 2 countries

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The Louisiana Department of Health today said that the state’s cases could reach a record high this year, part of national rise in cases. So far, the state has identified 164 cases in the first 4 months of 2025, putting it on track to record the most cases in at least 35 years. Cases have already passed the 153 pertussis cases reported for all of 2024. Since September 2024, 40 Louisiana residents have been hospitalized, 70% of them young babies. Two infant deaths have been reported, the state’s first since 2018. Officials urged parents to ensure that they and their children are up to date on recommended vaccine doses and that pregnant women receive the tetanus, diphtheria, and pertussis (Tdap) vaccine and that people who have contact with infants talk to their doctors about vaccination. The US Centers for Disease Control and Prevention (CDC) has said pertussis activity has returned to prepandemic levels, noting that cases in 2024 exceeded those levels and were six times higher than the previous year.
Following an announcement of three confirmed yellow fever cases earlier this week, Ecuador’s health ministry yesterday announced that it will begin requiring certain travelers to be vaccinated against the disease starting on May 12. They include visitors from Peru, Colombia, Bolivia, and Brazil and others who have spent more than 10 days in those countries before coming to Ecuador. Officials also said Ecuador residents who are traveling to high-risk areas on the country’s Amazon region must be vaccinated against yellow fever at least 10 days before traveling. In March, the Pan American Health Organization (PAHO) warned of a rise in cases and an expansion of the disease in some parts of South America. In mid-April, Colombia issued a public health emergency due to yellow fever circulation in several regions of the country.
Two countries reported more polio cases this week, including Pakistan, with two more wild poliovirus type 1 (WPV1) cases, the Global Polio Eradication Initiative (GPEI) said in its latest weekly update. The patients are from two districts of Khyber Pakhtunkhwa, raising the country’s total for the year to eight cases. Elsewhere, Nigeria reported three circulating vaccine-derived poliovirus type 2 (cVDPV2) cases with paralysis onsets in March. The patients are from Sokoto and Yobe states, pushing the country’s total for the year to 14 cases.

CDC: 12 more children die of flu, reaching new season high for a nonpandemic year

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Twelve more US children have died of influenza, surpassing the previous high for a flu season after the COVID-19 peak, the Centers for Disease Control and Prevention (CDC) said in its weekly update today.

The pediatric deaths push the season total to 216, surpassing last season's total of 207. Ten of the children died of influenza A, and two died from influenza B. Among the 8 fatal cases for which subtyping was performed, 4 were caused by the H1N1 strain and 4 by the H3N2 strain.

Flu activity as a whole, however, continues a slow decline, with outpatient visits for influenza-like illness (ILI) down to 2.2% from 2.4% last week. Hospitalizations have also dropped to 2,857 from 3,601.

No states reported moderate, high, or very high ILI levels; last week, one state each noted high or moderate ILI activity. Flu test positivity slid from 5.6% last week to 4.6%, but the cumulative hospitalization rate edged up slightly from 126.6 per 100,000 last week to 127.4 cases per 100,000—the highest since 2010-11.

COVID-19, RSV activity still low

CDC data updates today show low levels of COVID-19 activity. Two states, Minnesota and Missouri, recorded high levels of COVID-19 concentrations in wastewater, up from one (Louisiana) last week. The proportion of overall deaths caused by COVID-19 was 0.6%, compared with 0.7% last week and 0.2% for flu.

The percentage of COVID-19 infections caused by the dominant Omicron subvariant, LP.8.1, was the same as last week, at 69%, followed by XEC (10%) and LF.7.7.2 (6%), the CDC variant tracker shows.

Utah is the only state reporting moderate levels of influenza A wastewater activity, while the rest are low or very low, as are all respiratory syncytial virus (RSV) levels.

VA study: Pfizer COVID booster 68% effective against hospitalization

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Stephanie Soucheray, MA

COVID-19 vaccines — *Camosun College / Flickr cc*

A study published earlier this week in Nature Communications using claims data from the US Veterans Affairs (VA) Healthcare System finds protection from the 2024-25 Pfizer COVID-19 vaccine was 68%, 57%, and 56% against COVID-19–associated hospitalizations, emergency department and urgent care (ED/UC) visits, and outpatient visits, respectively.

However, the authors caution that uptake of the vaccine was extremely low—only 3.7% through November 2024—and the study did not assess waning effectiveness.

The study estimated early BNT162b2 KP.2 (2024-25 formulation) vaccine effectiveness (VE) against COVID-19 outcomes compared to not receiving the vaccine.

In total, 44,598 acute respiratory illness (ARI) encounters with valid SARS-CoV-2 test results were included in the final analysis. Overall, 16.2% (7,224) tested positive for SARS-CoV-2, and 1,666 (3.7%) received the BNT162b2 KP.2 vaccine; 138 of 7,224 COVID-19 patients (1.9%) and 1,528 of 37,374 controls (4.1%) received the vaccine.

Overall VE was 56% against all outcomes

Adjusted VE of the BNT162b2 KP.2 vaccine (compared to not receiving a KP.2 strain-adapted vaccine of any kind) against all COVID-19 outcomes was 56% (95% confidence interval [CI], 48% to 63%).

Additional efforts to improve COVID-19 vaccine uptake to match that of annual influenza vaccine coverage are needed.

Among patients who previously received one or more doses of the XBB vaccine, the adjusted VE of the KP.2 vaccine compared to not receiving the KP.2 vaccine was 77% (95% CI, 50% to 89%), 60% (95% CI, 48% to 69%), and 62% (95% CI, 43% to 75%) against hospitalizations, ED/UC visits, and outpatient visits, respectively.

"Despite this persistent burden and the increased protection observed with receiving updated vaccines over the last two respiratory virus seasons, uptake of updated COVID-19 vaccines remains low, even among older adults," the study authors wrote. "Additional efforts to improve COVID-19 vaccine uptake to match that of annual influenza vaccine coverage are needed."