The ‘twindemy’ of flu and coronavirus feared by public health officials has so far not materialized.
Influenza usually kills tens of thousands of Americans and can make hundreds of thousands of hospitalizations during the winter season. But this year, it has been virtually completely filled in the Bay – a fortune that is needed as coronavirus cases, hospitalizations and deaths increase uncontrollably across the country.
“Flu is not actually present in Northern California at this point,” said Dr. Randy Bergen, a specialist in childhood disease infections at Kaiser, is also the clinical head of Northern California’s flu vaccine program. “Our hospitals are always full during the winter, and in normal years it is due to flu. It’s a very abnormal year, but it’s because of another respiratory virus. ”
In a typical year, there is about 20% -40% positive rate for flu tests in the hospital, Bergen said, but this year doctors do not really anticipate such cases. About one in four patients who come to the hospital for respiratory symptoms test positive for the coronavirus, but the other three are for something else: not the coronavirus, not the flu, and not respiratory synthesis virus, or RSV, a other common respiratory virus. which annually accounts for thousands of deaths in the US, but also fell completely off the map.
Dr. Gary Green, a specialist in infectious diseases at Sutter Medical Group of the Redwoods in Santa Rosa, says doctors have only seen sporadic cases of flu A and flu B – with more and more flu A.
The minimal flu season in the Bay reflects what has already been shown in the Southern Hemisphere, in places like Australia, New Zealand and South Africa, where the flu season has passed without speaking. The same trend is now being reflected in the US and California, which are using much lower prices than usual this season.
According to Centers for Disease Control and Prevention data, which records doctor visits for flu-like symptoms as a percentage of total visits, California has hovered between 1% and 2% since the beginning of October 1st. by this time it varies between 3.5% and 6.5%.
Reports from the California Department of Public Health’s flu surveillance program, which detects the flu in weekly reports, paint an even more surprising picture of a flu season that has gone off the radar.
Take, for example, the first week of January, which marks the halfway point of the flu season, when cases and hospitalizations usually peak. In the 2019-20 season, there were widespread flu activities in the state during the week, with more than 26.9% tested positive for flu in the laboratory, 19 outbreaks and 70 deaths for the season up to that point. Hospitalizations were above expected levels.
The 2020-21 report could not have looked any different, with 0% flu shots in the hospital, a positive test score of 0.3% for flu in the laboratory and no outbreaks since the fall. Seven deaths have been reported, but a map of California shows almost no flu activity in the state.
So what happened?
So far, some experts have linked the quiet season of the year with a robust effect of flu vaccines, causing people to shoot, some for the first time and much earlier than usual. But that still does not explain the silence, says Dr. Lawrence Drew, a retired virologist who headed the UCSF Clinical Virology Laboratory.
“The best we’re ever seeing in the US for vaccine collaboration is 50-60%, and that would not be enough to explain it, nor would it explain the RSV,” he said.
Drew said some people also attributed the quiet season to an idea called viral interference, when an organism infected with one virus somehow resists infection with a second virus. But even that seems unlikely, he said, because it usually carries similar viruses – and flu, SARS COV-2 and RSV are not the same.
What the most likely explanation, says Drew and other experts, is that the pandemic measures for the public health of masking and social distance are very effective in preventing the spread of flu and RSV – even more so than for the spread of the coronavirus.
There is a scientific basis for this: studies have shown that SARS COV-2 is much more transmissible than the major seasonal respiratory viruses, including influenza and RSV. A new variant of the coronavirus, which has migrated to the US and California, is even more contagious, with some figures indicating a 70% increase in transmissibility.
According to the CDC, flu activity is extremely low in the country this season. Although California has now surpassed the country’s rate of flu-like illness, such increases are not uncommon in flu seasons. It can also be linked to the increasing increases in coronavirus cases by the state, mostly in Southern California, which officials have attributed in part to the sluggish adherence to public health guidelines. (By this time last year and at the beginning of the current flu season, California’s average was lower than the country’s.)
At the end of December, doctor visits for flu-like diseases in California were 2.3% of the total visits, while the country’s rate was 1.6%. Drew suspects that the Bay Area may be doing better than other parts of the state – and country – that may not adhere so strictly to public health guidelines.
According to Bergen, the specialist for childhood infectious diseases in Kaiser, there could be another “wild card” factor, according to Bergen: Flu seasons almost always start in schools, and most schools in the Bay are still remote or hybrid, with mask- wear and social distance.
The effects of the coronavirus vaccine in California and the US have started slowly, and the long COVID-19 year is probably months away from being under control. And the flu season does not always peak in December or January, Bergen said. As a result, if people stop wearing masks, take social distances, and follow hand hygiene, a twin anemia may still be imminent.
Drew’s long view is even more urgent. If people come out of this flu season and approach next time as if this one never happened – avoid masking, social distance and so on – all safety will be reversed. According to him, the guidelines that have helped us to avoid the flu this year are of the utmost importance.
“In a few years – five or ten or maybe just one – we’re going to have a flu pandemic,” Drew said, adding that variants are likely to emerge for which scientists do not have vaccines. “Everyone knows that. … There is no doubt about it. We are in arrears. ”
Annie Vainshtein is a San Francisco Chronicle staff writer. Email: [email protected] Twitter: @annievain