The Pan American Health Organization (PAHO) on May 31 issued an epidemiological alert about a rise in pertussis cases in a number of countries in the Americas, which comes in the wake of a sustained decline in pertussis vaccine coverage that gained traction during the COVID-19 pandemic period.

The average global pertussis case total declined sharply during the pandemic, reaching a historical low in 2021. Since then, cases have been on a steady rise. In the Americas, cases in 2012 were at their highest point in a decade, then fell progressively until 2022, but began rising again in 2023 with about 4,100 cases in the region. In 2024, the Americas logged nearly 44,000 cases. 

After the pandemic, pertussis vaccination showed a partial rebound in the Americas, though coverage varies between and within countries.

US leads countries reporting recent spikes

PAHO focused on seven Americas countries that are seeing rising cases in 2025, with the United States reporting the most cases, 10,062 as of late April. Five deaths were reported, four of them in children younger than 1 year old. States with the highest case numbers are Washington, Oregon, and California, and the most affected age group are children ages 11 to 19 years old.

Other countries reporting rises this year include Brazil, Mexico, Ecuador, Peru, Colombia, and Paraguay.

The group urged countries to enhance their surveillance systems for the disease, including the tracking of vaccine coverage, especially to identify gaps in the youngest children who are most at risk for the disease.

Vaccine maker Moderna announced late last week that the Food and Drug Administration (FDA) has approved its next-generation COVID-19 vaccine.

Marketed under the name mNexspike (mRNA-1283), the updated shot targets a portion of the SARS-CoV-2 spike protein for virus neutralization, allowing for a dose that's one-fifth the size of Moderna's original COVID-19 vaccine, Spikevax (mRNA-1273). Company officials have also characterized the updated shot as potentially refrigerator-stable vaccine that could be more easily distributed and administered in a wider range of settings.

Moderna said the approval was based on the results of a phase 3 randomized controlled trial involving 11,400 participants ages 12 and older, which found that a 10-microgram (μg) dose of mNexspike demonstrated a 9.3% higher relative vaccine efficacy (rVE) compared with a 50-μg dose of Spikevax, with a 13.5% higher rVE in adults ages 65 and older. The safety profiles of the two vaccines were similar, the company added.

"The FDA approval of our third product, mNEXSPIKE, adds an important new tool to help protect people at high risk of severe disease from COVID-19," Stéphane Bancel, CEO of Moderna, said in a company press release. "COVID-19 remains a serious public health threat, with more than 47,000 Americans dying from the virus last year alone."

Limited approval

Moderna said it expects to have mNexspike available for the 2025-26 respiratory virus season, alongside Spikevax. But, under the new COVID-19 vaccine framework outlined recently by FDA Commissioner Martin Makary, MD, MPH, and Vinay Prasad, MD, MPH, director of the FDA's Center for Biologics Evaluation and Research, mNexspike is approved for use only in adults 65 and older and people aged 12 to 64 years with at least one condition that puts them at higher risk for severe disease. 

Spikevax currently remains available for use in anyone 6 months and older.

A retrospective analysis of patients at Veterans Affairs (VA) hospitals found that influenza and respiratory syncytial virus (RSV) is associated with increased risk of secondary Streptococcus pneumoniae infection but COVID-19 isn't, researchers reported late week in Clinical Infectious Diseases.

The study, led by researchers with the VA Western New York Healthcare System, analyzed data on patients who received care and were tested for S pneumoniae at VA hospitals from January 2015 through March 2025. Patients positive for S pneumoniae were assessed for evidence of prior flu, RSV, and COVID-19 infections. The primary outcome was development of S pneumoniae infection within 30 days after a positive test for flu, RSV, or COVID-19.

Of the 188,172 patients (mean age, 70 years; 96% male) included in the study, 8,165 (4.3%) were positive for S pneumoniae. The incidence of S pneumoniae in patients varied with respiratory viral testing for COVID-19, RSV, and influenza. Among all patients, there were 14,506 cases of positive COVID-19, of which 336 (2.3%) subsequently had S pneumoniae infection, along with 1,349 cases of RSV and 4,504 cases of influenza, of which 132 (9.8%) and 452 (10.0%) involved subsequent positive tests for S pneumoniae, respectively.

Higher risk with flu, RSV

In the multivariable logistic regression analysis, both flu (odds ratio [OR], 2.39; 95% confidence interval [CI], 2.15 to 2.64) and RSV (OR, 2.50; 95% CI, 2.07 to 2.99) more than doubled the odds of subsequent S pneumonia infection. But prior COVID-19 infection decreased the odds by 44% (OR, 0.56; 95% CI, 0.50 to 0.62). Current smokers (OR, 1.09; 95% CI 1.03 to 1.16) and those with chronic obstructive pulmonary disease (OR, 1.36; 95% CI 1.28 to 1.45) were also associated with increased odds of subsequent S pneumoniae.

The study authors say flu or RSV may increase the risk of S pneumoniae infection by damaging the bronchi and lung epithelium, which may create more attachment sites for bacteria. But why COVID-19 was associated with reduced S pneumoniae risk is unclear.

"In the post-viral setting of influenza or RSV, empiric antimicrobial therapy with coverage for S. pneumoniae should be considered in patients presenting with clinical features suggestive of bacterial superinfection," they wrote.

Researchers conducting a lab study published on the preprint server medRxiv detected infectious flu viruses in raw cow and sheep milk for over a day at room temperature and more than a week when refrigerated.

The results of the non–peer-reviewed research highlight the risk of contracting H5N1 avian flu from consuming unpasteurized dairy products and from occupational exposure in dairies, the UK investigators said.

After the emergence of H5N1 in US dairy cattle in late 2023, "high viral titres were detected in milk from infected cows, raising concerns about onwards human infections," they wrote. "Although pasteurisation was shown to effectively inactivate influenza viruses in milk, unpasteurised milk still poses a risk of infection, both from occupational exposure in dairies and from the consumption of raw milk." 

H5N1 has been detected in more than a thousand US cattle herds, other mammals, dozens of dairy workers, and several people with no direct contact with infected animals.

'Substantial viral infectivity remained'

The team assessed the stability of H5N1 highly pathogenic avian influenza virus (HPAIV) and other influenza A and D viruses by incubating them in pasteurized cows' milk at room temperature to represent exposure in dairies and at 4°C [39.2°F] to simulate exposure to refrigerated raw milk. They also conducted similar experiments with a lab strain of avian flu in sheep's milk.

Our results highlight the zoonotic risk of H5N1 HPAIV in raw milk from infected animals and reinforce the importance of taking measures to mitigate this risk.

"Although the survival of influenza viruses in milk was variable, we consistently found that under laboratory conditions substantial viral infectivity remained over periods when people might reasonably be exposed to infected milk—for over a day at room temperature and for more than 7 days when refrigerated," the authors wrote. 

"Our results highlight the zoonotic risk of H5N1 HPAIV in raw milk from infected animals and reinforce the importance of taking measures to mitigate this risk," they added. "Our experiments aimed to model the 'worst case scenario' for the persistence of viral infectivity in milk and should be seen as providing an upper-bound estimate for viral survival under real-world conditions."