A ‘tripledemic’? Flu and other infections return as Covid-19 cases rise in the US

A Covid-19 test site at the Esperanza Health Centre in Chicago on Sept 13, 2022. PHOTO: NYTIMES

NEW YORK - For more than two years, shuttered schools and offices, social distancing and masks granted Americans a reprieve from flu and most other respiratory infections. This winter is likely to be different.

With few to no restrictions in place and travel and socialising back in full swing, an expected winter rise in Covid-19 cases appears poised to collide with a resurgent influenza season, causing a so-called “twindemic” – or even a tripledemic, with a third virus, respiratory syncytial virus, or RSV, in the mix.

Cases of flu have begun to tick up earlier than usual and are expected to soar over the coming weeks. Children infected with RSV –which has symptoms similar to those of flu and Covid-19 – rhinoviruses and enteroviruses are already straining paediatric hospitals in several states.

“We’re seeing everything come back with a vengeance,” said Dr Alpana Waghmare, an infectious diseases expert at Fred Hutchinson Cancer Centre and a physician at Seattle Children’s Hospital.

Most cases of Covid-19, flu and RSV are likely to be mild, but together they may sicken millions of Americans and swamp hospitals, public health experts warned.

“You’ve got this waning Covid-19 immunity, coinciding with the impact of the flu coming along here, and RSV,” said Dr Andrew Read, an evolutionary microbiologist at Penn State University. “We’re in uncharted territory here.”

RSV causes about 14,000 deaths among adults aged 65 and older and up to 300 deaths among children younger than five each year. No vaccine is available, but at least two candidates are in late-stage clinical trials and appear to be highly effective in older adults. Pfizer is also developing an antiviral drug.

Covid-19 cases are low but are beginning to rise in some parts of the United States. Several European countries, including France, Germany and Britain, are experiencing an uptick in hospitalisations and deaths, prompting experts to worry the US will follow suit, as it has with previous waves.

Some of the coronavirus variants that are picking up momentum are adept at dodging immunity and drugs such as Evusheld and Bebtelovimab, which are especially important for protecting immunocompromised people.

People with weakened immune systems “remain at risk even despite getting all the recommended or even additional doses of vaccine”, Dr Waghmare said.

Public health experts are particularly concerned about a constellation of Omicron variants that seem to dodge immunity from the vaccines and even from recent infection better than previous variants did.

The latest booster vaccines made by Pfizer and Moderna were designed for the variants that dominated this past summer but not for these newer variants. Still, they raise antibody levels overall, and should help stave off severe symptoms and abridge the duration of illness, said Dr Aubree Gordon, a public health researcher at the University of Michigan.

Bins storing vaccines at Ted Watkins Memorial Park in Los Angeles, on March 31, 2022. PHOTO: NYTIMES

The BA.5 variant was the most immune-evasive variant until recently, but it is rapidly being replaced by others, including two that show an even greater ability to sidestep immunity.

One of them, known as BQ.1.1, is the leading candidate for causing a winter wave. It has already sent cases soaring in Europe. Although it and a closely related variant called BQ.1 together account for only about 11 per cent of cases in the US, their share has grown rapidly from just 3 per cent two weeks ago.

A combination of two Omicron subvariants called XBB has been fuelling a wave of cases in Singapore, among the most highly vaccinated nations in the world. Its subvariant XBB.1 has just arrived in the US. Another variant, called BA.2.75.2, is also highly immune evasive and causes more severe disease, but is so far responsible for less than 2 per cent of cases nationwide.

Before Covid-19 walloped the world, flu viruses sickened millions each winter, and killed tens of thousands of Americans. In the 2018 to 2019 season, the flu was responsible for 13 million medical visits, 380,000 hospitalisations and 28,000 deaths.

Flu season in the Southern Hemisphere, typically between May and October, is highly predictive of winters in the Northern Hemisphere. This year, flu began weeks earlier than usual in Australia and New Zealand, and the numbers of cases and hospitalisations were markedly higher.

Dr Gordon tracks influenza rates among children in Nicaragua, which has a flu season spanning June and July and a larger one in the late fall. More than 90 per cent of the population were considered fully vaccinated against Covid-19 by last January, and many people had also gained immunity from one or more infections.

Still, the country saw high rates of both Covid-19 and influenza in the first half of 2022. Influenza rates among children were higher than in the 2009 flu pandemic, and the children were sicker on average than in previous years. “We saw a lot of hospitalisations,” said Dr Gordon.

In the US, flu typically begins to pick up in October and runs through March, peaking some time between December and February. But in some states, the season is already under way.

About 3 per cent of tests nationwide were turning up positive for flu as at Oct 8, according to the Centres for Disease Control and Prevention. The rates are higher than 10 per cent in some south-eastern states and more than 5 per cent in the South Central region. In Texas, the proportion of tests positive for flu jumped to 5.3 per cent in early October from 3.7 per cent the week before.

Some communities are at increased risk of severe illness and hospitalisation for flu. During flu seasons from 2009 to 2022, rates of hospitalisation were 80 per cent higher among Black adults, 30 per cent higher among American Indian/Alaska Native adults and 20 per cent higher among Hispanic adults compared to white adults, according to a CDC report released last week.

Yet, flu vaccination rates were much lower in these groups. Vaccine coverage also declined by about 9 percentage points from the previous year in pregnant women across all racial and ethnic groups.

NYTIMES

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