Yes, everyone really is sick a lot more often after covid

Since February, Kathy Xiang and her entire family have been under siege.

Her 12-year-old daughter has had whooping cough, rhinovirus and parainfluenza: She's missed more than five weeks of school in total. Xiang, a software developer in Shanghai, caught all three too. Her elderly parents, who were helping care for her 10-month-old, tested positive for Covid-19 in early March, and her father got shingles.

Then the baby caught parainfluenza and pneumonia, necessitating five days on an IV drip. "I was literally numb after the baby boy got sick despite all our efforts to protect him," Xiang said. "I was physically and mentally exhausted."

Around the world, a post-Covid reality is beginning to sink in: Everyone, everywhere, really is sick a lot more often.

At least 13 communicable diseases, from the common cold to measles and tuberculosis, are surging past their pre-pandemic levels in many regions, and often by significant margins, according to analysis by Bloomberg News and London-based disease forecasting firm Airfinity Ltd.

The resulting research, based on data collected from more than 60 organisations and public health agencies, shows that 44 countries and territories have reported at least one infectious disease resurgence that's at least ten times worse than the pre-pandemic baseline.

The post-Covid global surge of illnesses — viral and bacterial, common and historically rare — is a mystery that researchers and scientists are still trying to definitively explain. The way Covid lockdowns shifted baseline immunities is a piece of the puzzle, as is the pandemic's hit to overall vaccine administration and compliance. Climate change, rising social inequality and wrung-out health-care services are contributing in ways that are hard to measure.

Covid-19 is the first major global pandemic in the era of modern medicine, so there's little precedent for what comes after. "The last major devastating flu pandemic was in 1918. There was no vaccination, no diagnostics or treatments. So we are in a new territory here," said Jeremy Farrar, World Health Organization's chief scientist.

Comeback Diseases

Influenza cases in the US have jumped about 40% in the two post-Covid flu seasons, compared with the pre-pandemic years, according to clinical lab results. Whooping cough, or pertussis, cases have climbed by 45 times in China in the first four months compared with last year. And in some parts of Australia, where flu season is just getting underway, cases of respiratory syncytial virus, or RSV, have nearly doubled from a year ago.

Argentina is battling its worst-ever dengue outbreak. Japan is seeing a mysterious surge of Streptococcal A, also known as strep throat. Measles is making a comeback in more than 20 American states, the UK and parts of Europe. Globally, 7.5 million people were newly diagnosed with tuberculosis in 2022 — the worst year on record since the World Health Organization started global TB monitoring in the mid-1990s.

The theory of immunity debt has become a popular, if controversial, explanation for the post-Covid surge in illnesses. It basically means that pandemic lockdowns offered an artificial layer of insulation from routine pathogens but left people more vulnerable when the world reopened. The effect is worse for young kids, whose brand-new immune systems were cosseted by social distancing, online classes and masks.

PERU-HEALTH-EPIDEMIC-DENGUE

By April 2024, dengue fever cases in the Americas passed the total for the previous year. Above, a patient outside Lima, Peru, in April.Photographer: Juan Carlos Cisneros/AFP/Getty Images

"It's like the walls of the immune system are broken, so all kinds of viruses can easily get in," said Cindy Yuan, an internal medicine doctor in a private clinic in Shanghai. In some months, she says, her patient load has doubled from pre-Covid levels. "It's nonstop. From last autumn's mycoplasma infections to flu and Covid during winter, and then whooping cough and various kinds of bacteria infections."

That's been the leading explanation for the extra traffic at paediatric hospitals globally since the 2022 flu season and for why respiratory pathogens returned with such a vengeance, like in China's first post-Covid Zero winter last year.

Public health experts aren't convinced. Immunity debt might account for some resurgence of illnesses reported post-Covid, but probably not all of it, said Ben Cowling, chair of epidemiology at the University of Hong Kong's School of Public Health.

"Immunity debt, it definitely happens, but I don't think it results in enormous epidemics after Covid," he said, adding that greater surveillance and testing could also contribute to higher reported numbers.

What's more, if immunity debt were the only factor, the countries that lifted pandemic restrictions two or three years ago should be caught up by now, and they're not. The waves of illnesses keep coming.

So do fatalities. A sustained rise in mortality levels in some countries is fueling another theory, that pandemic lockdowns essentially kept some people alive who may have died in a normal environment with freely-circulating viruses and bacteria.

The Biggest Risk

Canada, Japan, Singapore and Germany — places lauded for their successful efforts to contain Covid — are now seeing unusual levels of excess mortality, said Christopher Murray, Washington-based director of the Institute for Health Metrics and Evaluation. In contrast, places that failed to control the spread of Covid, like Bulgaria, Romania and Russia, are now back to pre-pandemic mortality rates.

"Why would it be worse in places that did a good job? That seems a bit strange. Some of this is the idea that those countries kept frail, elderly people alive," Murray said. Mixed with the immunity debt theory, "it's a really quite complicated set of things going on," he said.

Then there's the unquantifiable role of poverty, which has spiked globally in the aftermath of the pandemic. Social inequality is the "biggest risk factor" for infectious disease, said David Owens, co-founder of OT&P Healthcare in Hong Kong. Overcrowded living conditions and poor access to high-quality nutrition adds to illness, increasing the amount of viral and bacterial pathogens in societies. And the ensuing strain on public health-care systems drags down the quality of care for everyone.

"Having vulnerable populations which allow an epidemic to take hold or accelerate increases risks for everybody," Owens said.

ZAMBIA-LUSAKA-CHOLERA TREATMENT CENTER

Cholera outbreaks have become more deadly, with decade-high fatality rates. Above, a temporary treatment centre in Lusaka, Zambia.Photographer: Peng Lijun/Xinhua/Getty Images

Missed Shots

The spikes in preventable illnesses, like measles, polio and pertussis are easier to explain, experts say. Vaccination rates fell sharply during the pandemic, with supply chains disrupted, resources diverted and immunisation services limited by lockdowns, Cowling said.

At the same time, a growing number of children live in conflict or fragile environments, limiting ready access to vaccines. And Covid-era misinformation fueled simmering mistrust in vaccines in general.

About 25 million children missed at least one dose of the three-shot diphtheria, tetanus and pertussis vaccine in 2021. The percentage of children who received all the three doses of this vaccine dropped to 81%, the lowest level in 13 years.

UNICEF Executive Director Catherine Russell called it "a red alert for child health" in July 2022. "The consequences will be measured in lives," she warned then.

Pertussis, which can induce coughing fits so violent that patients have been known to break their ribs, has been staging a global comeback. Deaths, usually in young babies who struggle to breathe, have been reported in China, the Philippines, the UK, the Czech Republic and the Netherlands. Canada, South Africa, Bolivia, the US, Malaysia and Israel have all seen resurgent outbreaks.

Measles — identified through a distinctive dotted rash, coughing and a fever that can be deadly for young children — is an extremely contagious virus, requiring a very high threshold vaccination rate of about 95% in young children to stop its spread.

In the UK, coverage for the second measles dose was just over 84% in 2022-23 for five-year-olds, far below what's needed for community protection. In Europe, more than 1.8 million infants in Europe missed their measles shot between 2020 and 2022, and the region saw a 30-fold spike in cases last year. The US eliminated measles in the year 2000, but the disease has returned after a dip in kindergarten inoculation.

Measles, says University of Illinois epidemiologist Katrine Wallace, is an early warning sign, the first indication that vaccination rates are dropping to the point that other diseases are going to come back.

"Every one of these diseases has kind of its own story, its own risk factors, its own geographical considerations," Wallace said. "It's like putting together a series of puzzles."

Sick Days

The consequences of Covid can be thought of as "a series of concentric circles," said WHO's Farrar. The acute public health emergency has ended, but the knock-on effects persist.

The state of constant illness already is taking a toll on businesses and the economy. Nearly one in three US employees in white-collar jobs took at least one sick day in 2023, according to payroll company Gusto, up 42% from 2019. And when they missed work, they missed more of it, with the average absence up 15%. And a UK study found workplace absences at the highest rate in over a decade, with employees missing nearly eight days on average over the past year, up from six before the pandemic.

To move past the current situation, rebuilding society's trust in vaccines is an absolute must, said Farrar. "We've got to make the case for science and for vaccines and explain and explain and explain the importance. We can't just say some people are anti-science or anti-vaccine and forget them," he said. "We need to listen, explain, and try to reach everybody."

The surge in RSV, influenza, whooping cough and even the common cold is taxing public health resources. Above, waiting for a doctor's appointment in Barcelona.Photographer: Emilio Morenatti/AP Photo

Despite the speed with which countries around the world left Covid-era protections behind, the lingering trail of sickness, along with the thousands of Covid deaths each month, shows that the pandemic has cast a long shadow. The Spanish flu persisted for roughly three years, IHME's Murray said.

Given three years have already passed since Covid arrived, "we were very surprised with the 2023 patterns in some of these countries," he said. "Maybe we have more surprises coming."

Data Methodology

Bloomberg News collaborated with Airfinity to map the post-pandemic resurgence of 13 infectious diseases. The spike size is determined by the fold change, or ratio, in the peak reported cases during a post-pandemic period (2022-onward) compared with the pre-pandemic maximum annual incidence between 2017 and 2019. The baseline year for pertussis for some countries may be set to an earlier date to capture the most recent outbreak before the pandemic.

The analysis includes chickenpox, cholera, dengue, measles, mycoplasma pneumoniae, parvovirus B19, invasive Group A Streptococcus, pertussis, influenza, RSV, wild poliovirus type 1, vaccine-derived poliovirus and tuberculosis. The global spike map illustrates only six diseases with most notable resurgences.

The analysis, as of June 1, relies heavily on data reported by countries or regions and may not be exhaustive. Data from some geographies may be more accurate due to superior surveillance and reporting systems. Some regions have also seen higher testing, which may have increased the disease incidence.

The year-to-date data has been included in the research since significantly higher cases are being recorded for certain diseases in 2024 than in any other year included in the study. In such instances, the fold change is calculated based on cases reported so far this year, with the assumption that these figures will rise as more data becomes available over time.

— With assistance from Lulu Shen, Daniela Wei, Jason Gale, and Yasufumi Saito