More than five years since the first reported cases of COVID-19 in Wuhan, China, and after more than 20 million deaths globally, the world is still left without a definitive answer to the question that has haunted scientists, politicians, and the public alike: How did COVID-19 begin?

The origins of COVID-19, the pandemic that has reshaped the 21st century, remain one of the most pressing and contentious mysteries in global health. After more than three years of investigation, the World Health Organization’s (WHO) expert group has released its final report—yet the world is left with more questions than answers. Despite unprecedented scientific collaboration and scrutiny, the true source of SARS-CoV-2, the virus responsible for COVID-19, remains elusive.

The World Health Organization (WHO), after years of probing, released its final report through the Scientific Advisory Group for the Origins of Novel Pathogens (SAGO), offering an unsettling conclusion — the origin of SARS-CoV-2 remains unconfirmed. While the report aligns with the hypothesis that the virus likely spilled over from animals to humans, it stops short of ruling out a laboratory-related incident due to a critical lack of evidence.

At the core of the WHO investigation is the zoonotic spillover theory — the widely supported scientific view that SARS-CoV-2 originated in animals and jumped to humans. According to Marietjie Venter, chair of the SAGO expert group, “most scientific data supports the hypothesis that the new coronavirus jumped to humans from animals.”

This aligns with the WHO’s earlier 2021 mission to China, which also concluded that the virus most likely moved from bats to humans, potentially through an intermediary host. That earlier group had called a lab leak “extremely unlikely.” Since then, however, the landscape of inquiry has become increasingly politicized and restricted.

At a press briefing, SAGO chair Marietjie Venter summarized the group’s findings: “Most scientific data supports the hypothesis that the new coronavirus jumped to humans from animals.” This zoonotic spillover theory, suggesting the virus moved from bats to humans—possibly via an intermediary animal—remains the most widely supported scenario. This aligns with the conclusions of an earlier WHO investigation in 2021, which also found a natural origin most likely and considered a laboratory accident “extremely unlikely” at the time.

The Zoonotic Hypothesis

The scientific consensus points to a zoonotic origin, with bats as the primary reservoir for coronaviruses similar to SARS-CoV-2. The virus’s genetic makeup closely resembles that of bat coronaviruses, and several animal species, including civet cats, raccoon dogs, and bamboo rats, have been investigated as possible intermediate hosts. Studies have shown that the ACE2 receptor, which SARS-CoV-2 uses to enter cells, is present in a range of mammals, supporting the plausibility of animal-to-human transmission.

Recent research has narrowed the list of potential intermediary species but has not identified a definitive culprit. The lack of direct evidence—such as an animal sample with a virus genetically identical to early human cases—means the zoonotic pathway, while likely, cannot be proven beyond doubt

The Lab Leak Theory

Though some governments, including the United States under former President Donald Trump, have promoted the possibility that COVID-19 emerged from a lab accident in Wuhan, WHO’s recent report makes it clear that this theory remains speculative. “There is no evidence to prove that COVID-19 was manipulated in a lab,” said Venter. “Nor is there any indication that the virus had been spreading outside of China before December 2019.”

The WHO advisory group reported that despite repeated requests, they were unable to obtain essential data from Chinese authorities — including genetic sequences from early COVID-19 patients, detailed records of animals sold at the Wuhan seafood market, and biosafety logs from relevant Wuhan laboratories. These missing data points continue to impede the investigation.

Crucially, the report confirms that the lab leak theory could not be adequately evaluated or ruled out because “the necessary data was never made available.” Venter emphasized that “the hypothesis could not be investigated or excluded” and that speculation was mostly “based on political opinions and not backed up by science.”

Political Hurdles and Data Gaps

The search for COVID-19’s origins has been hampered by political tensions and a lack of transparency. The Chinese government has restricted the publication of research on the virus’s origins and has tightly controlled access to relevant data and sites. International investigators have faced obstacles, from denied access to key locations to the withholding of crucial genetic information.

These barriers have fueled speculation and mistrust, particularly regarding the lab leak theory. While some Western officials and scientists have called for more rigorous investigation of laboratory records and staff health data, Chinese authorities have repeatedly dismissed such inquiries and suggested the search for origins should expand to other countries.

In retrospect, the window for unbiased scientific investigation may have passed. An Associated Press (AP) investigation previously revealed that China clamped down on both domestic and international efforts to trace the virus’s origins in the early weeks of 2020. WHO, too, was accused of failing to act swiftly or assertively enough during the critical early months of the pandemic.

WHO Director-General Dr. Tedros Adhanom Ghebreyesus has repeatedly called uncovering the virus’s origins a “moral imperative.” At Friday’s press conference, he reiterated this point: “Understanding how COVID-19 began is not about blame — it is about science, preparedness, and protecting the world from future pandemics.”

While definitive answers remain elusive, scientific efforts to identify a possible intermediary animal host are ongoing. Last year, researchers narrowed their focus to several species — including raccoon dogs, civet cats, and bamboo rats — believed to have been sold at Wuhan’s Huanan Seafood Market.

However, WHO said that until China releases critical genetic sequences from both animals and early human cases, the mystery remains unresolved. “Until more scientific data becomes available, the origins of how SARS-CoV-2 entered human populations will remain inconclusive,” Venter admitted.

What This Means for the Future?

With each passing year, the trail of the virus grows colder. Biological samples degrade, memories fade, and geopolitical tensions deepen. Yet, the stakes remain enormous. As the world grapples with long COVID, vaccine fatigue, and the enduring socioeconomic scars of the pandemic, the need for clear, evidence-based origin tracing is more urgent than ever.

COVID-19 was not the first pandemic, and it will not be the last. As Dr. Tedros aptly put it, “We owe it to the millions of people who lost their lives to COVID-19, and to the billions whose lives were upended, to understand what happened and to ensure it never happens again.”

Three years on, the story of how COVID-19 began is still unfinished. The WHO probe has advanced our understanding but has also revealed the limits of science in the face of missing data and political barriers. For now, the world must contend with uncertainty, even as the search for answers continues. The origins of the pandemic may remain a mystery, but the imperative to learn, adapt, and prepare for the next global health threat has never been clearer.

An sudden spike in hepatitis A infection in several European countries has led to public health authorities issue urgent advisories and roll out containment strategies. The multicountry outbreak, spanning Austria, Czechia, Hungary, and Slovakia, has already infected more than 2,000 people since January 2025. The European Centre for Disease Prevention and Control (ECDC) confirmed on Friday that two genetically linked strains of the hepatitis A virus (HAV) are behind this multicountry outbreak, which alarms for ongoing community transmission and potential cross-border spillover.

Though hepatitis A is generally a preventable viral illness, its comeback in Europe is a grim reminder of how vaccination gaps, sanitation flaws, and outreach failures can prove lethal — particularly for older people and those who are vulnerable.

This outbreak, characterized by two similarly linked hepatitis A virus (HAV) strains, has not only affected local groups but also infected tourists traveling to popular tourist destinations in Europe. The problem is further complicated by reports of confirmed cross-border transmissions, with Germany reporting cases genetically associated with those in Austria and Hungary, indicating the likelihood for wider spread.

The cluster is focussed in four middle European countries: Slovakia (880), Czechia (600), Hungary (530), and Austria (87). Although all these countries have suffered the majority of the infections, cases that had the outbreak strain are also found within Germany, reflecting the virus's capacity to transcend borders via social networks and travel.

Nine fatalities have been reported to date — six in Czechia and three in Austria — underlining the potentially serious health impact of the disease, especially in older people or those with existing liver disease. The ECDC's rapid risk assessment also verifies genomic evidence of regionally linked transmissions, triggering a coordinated EU response.

What is Hepatitis A?

Hepatitis A is acute viral disease of the liver due to the hepatitis A virus (HAV). In contrast to its more persistent cousins, hepatitis B and C, hepatitis A does not result in chronic liver disease. But it can nevertheless generate full-blown disease and death—particularly among those at high risk.

The virus is mainly spread by ingestion of infected food or water, or direct contact with an infected person. HAV is found in the feces of infected individuals and is thus majorly a factor of poor sanitation and hygiene that leads to outbreaks. The illness quickly spreads in communities lacking clean water, safe food, and proper healthcare.

Contrary to hepatitis B and C, hepatitis A does not develop into chronic liver disease. Nevertheless, it may cause severe liver complications and even death in some people. Severity escalates with age. The ECDC has estimated the risk of serious illness as high in people older than 40 years and very high in individuals with pre-existing liver disease or weakened immunity.

Symptoms and Challenges in Early Detection

Not all people who get hepatitis A develop symptoms. But if symptoms do occur, they might include:

• Weakness and fatigue
• Abdominal pain and fever
• Jaundice, or yellow eyes and skin
• Clay-colored stools and dark urine
• Nausea and loss of appetite
• Diarrhea and joint pain

Since the virus takes weeks to manifest as symptoms, people may spread the virus unknowingly during incubation. That timing makes it harder to track the infections and contain possible routes of exposure.

Who Is Most at Risk?

Although anyone can get hepatitis A, there are groups that are more likely to suffer from severe illness. The ECDC states that individuals aged 40 years and older are at greater risk of developing serious complications, and the risk increases with age. Patients with existing liver disease and those who are immunosuppressed are especially at risk, as are older persons.

Social determinants also come into play. The epidemic has hit disproportionately hard among those living in homelessness, those who inject or use illicit drugs, and those living in filthy conditions or with limited healthcare access. These individuals usually do not have the resources necessary to receive vaccination or be at a hygiene standard to avoid infection.

For the population at large in the affected nations, risk is at present estimated as low to moderate. Yet, the situation is dynamic, and the risk for further transmission cannot be ruled out.

Slovakia has been struggling with hepatitis A since 2022, making it the epicenter of the current outbreak. Its 880 cases this year represent the largest burden across the affected nations. Czechia, meanwhile, has seen a significant jump in cases in 2025, including the majority of the deaths.

Even with the fewer cases reported, there have been three deaths in Austria — highlighting the fact that the virus does not have to be widespread to pose a threat. In Hungary, more than 500 cases of infection have been reported this year, leading health authorities to increase surveillance and prevention measures.

How the Virus Is Spreading?

Genetic sequencing has shown that the current outbreak is being fueled by person-to-person transmission in interconnected social networks and geographic regions. The fact that genetically similar strains were detected in Germany, where it is not an epicenter, is a testament to the ease with which the virus can travel across borders—particularly in an age of high mobility and international travel.

Though foodborne transmission cannot be ruled out, available evidence implicates close personal contact and unsatisfactory sanitation as main movers. This underscores the pivotal role that focused prevention and swift response play in high-risk populations.

The ECDC has called on member states to carry out epidemiologic studies, expand targeted contact with high-risk groups, and improve access to vaccination. Cross-border coordination has also been highlighted by the agency, since the outbreak does not respect geography or citizenship. Strategies that are recommended include:

• Targeted vaccine campaigns among high-risk groups
• Post-exposure prophylaxis (PEP) of close contacts
• Increased sanitation and hygiene in settlements and communities
• Increased genetic testing to track spread of virus
• Public education and awareness to increase early reporting and vaccination rates

ECDC's head of One Health Unit Ole Heuer highlighted the need for increased outreach: "This outbreak is a reminder that hepatitis A infection can lead to severe illness and death, particularly in individuals with poor access to health care and basic hygiene. Vaccination and sanitation services need to reach those who are most vulnerable."

How You Can Protect Yourself?

For people, the best defense against hepatitis A is vaccination. The hepatitis A vaccine is given in two doses, usually six to twelve months apart. The CDC says getting the vaccine — or immune globulin treatment — within two weeks of infection can ward off illness. Other important prevention measures are:

• Washing hands frequently with soap and water, particularly before meals
• Drinking clean, filtered water and avoiding suspect food sources while abroad
• Not getting direct exposure to the body fluid of infected people

The CDC also advises travelers to countries with outbreaks of hepatitis A to get vaccinated before they go.

As the peak travel season for summer draws near, it's a time of vigilance for public health officials and travelers alike. Vaccination, education, and enhanced sanitation are the pillars of prevention—not only for hepatitis A, but for the countless infectious diseases that still threaten global health security.

A federal vaccine advisory panel, newly reconstituted by U.S. Health Secretary Robert F. Kennedy Jr., has voted against thimerosal, a preservative long used in multi-dose flu vaccines, for use in all age groups. The recommendation, made by a unanimous vote, has caused shock waves in the medical and scientific communities, generating debate on vaccine safety, public confidence, and potential future availability of flu vaccines. The move revisits a debate many experts considered settled and could reshape how influenza vaccines are produced and distributed worldwide.

The newly restructured vaccine panel led by U.S. Health Secretary Robert F. Kennedy Jr. voted to advise against the use of thimerosal in flu shots given annually to millions of Americans. The move, taken by the Advisory Committee for Immunization Practices (ACIP), has raised alarm among scientists and public health professionals concerned the ruling could erode confidence in vaccinations and create disruptions in vaccine supplies, particularly during flu season.

In a 5-1 vote, with one abstention, ACIP members voted to limit thimerosal in all age groups for seasonal flu vaccines. The revamped panel, reorganized by Kennedy after she had all 17 of the agency's previous members dismissed over charges of conflict of interest, now includes appointees sympathetic to Kennedy's long-time vaccine skepticism.

"The threat from influenza is so much larger than the non-existent — to our knowledge, at least — threat from thimerosal," said Dr. Cody Meissner, professor of pediatrics at Dartmouth's Geisel School of Medicine and the lone dissenter. "I would be sorry if an individual did not get the influenza vaccine because the only product available contains thimerosal."

The Advisory Committee on Immunization Practices (ACIP), which advises the Centers for Disease Control and Prevention (CDC) on vaccine policy, is now in the middle of a storm. In June, Kennedy replaced all 17 of the former members, citing conflicts of interest, and appointed eight new members, many of whom are like-minded skeptics of vaccine safety. Five voted for, one voted against, and one abstained to limit thimerosal in flu vaccines.

What is Thimerosal?

Thimerosal is an ethylmercury-containing preservative that was first used in the 1930s to stop bacterial contamination of multi-dose vaccine vials. The compound in thimerosal, ethylmercury, is different from methylmercury—the form present in seafood—which is stored in the body and carries known health dangers. Ethylmercury, however, is metabolized and eliminated much faster.

The dose of ethylmercury from a standard dose of flu vaccine (25 micrograms) is about half that in a 3-ounce serving of canned tuna (40 micrograms) Thimerosal has been eliminated from almost all routine pediatric and most adult vaccines in the U.S. since the early 2000s as a precaution, even though there was no evidence to implicate it in harm. Now it still appears in only around 5% of multi-dose vials of flu vaccine.

Why Is Thimerosal Controversial?

Thimerosal became controversial in the late 1990s because it contains mercury and was theorized to cause autism and other neurodevelopmental disorders. Despite repeated, large-scale studies conducted in many countries, numerous studies have determined that there is no connection between thimerosal and neurological injury. The Centers for Disease Control and Prevention, the World Health Organization, and many scientific organizations have all determined that thimerosal, when administered in vaccines, is safe.

The preservative has never been part of the MMR vaccine, as is often incorrectly stated. Now, nearly 96% of all flu shots in the United States are thimerosal-free, with only a few kept to serve multi-dose vials for cost-effectiveness and logistical purposes.

Despite this, thimerosal was a rallying cry for anti-vaccine activists, including Kennedy himself. Thimerosal-autism theories have been repeatedly discredited, and the preservative was voluntarily phased out from most childhood vaccines in the U.S. by 2001. Significantly, the rates of autism continued to increase even after the removal of thimerosal, further eroding the supposed connection.

Several large-scale international studies have identified no link between thimerosal and autism or other neurologic problems. A standard flu shot with thimerosal contains approximately 25 micrograms of ethylmercury — half as much mercury as in a 3-ounce tuna can. Ethylmercury is excreted from the body in approximately a week, with no potential for bioaccumulation.

In addition, studies indicate that autism rates have continued to climb even since thimerosal was phased out of children's vaccines in the early 2000s, further refuting the theory that it is responsible for developmental disorders.

Implications for Flu Season and Global Vaccine Supply

Whereas the panel again emphasized that all Americans above six months of age should be vaccinated against flu, the vote will potentially restrict access in some settings. Several clinics, particularly in low-income or rural areas, depend on multi-dose thimerosal-containing vials because they are less expensive and easy to store.

Experts are concerned that the suggestion might trigger unnecessary shortages or access blockages for underprivileged groups. It also has the potential to impact international vaccine policies, especially in low- and middle-income nations where thimerosal-containing vaccines are still important for logistical and economic reasons.

Today, 96% of flu vaccines given in the U.S. are thimerosal-free, with even greater percentages in federal programs such as Vaccines for Children. The majority of children already receive thimerosal-free single-dose vaccines. Nevertheless, the few remaining multi-dose vials are important to maintaining overall vaccine coverage, especially during peak demand or when supplies are low.

Although the U.S. has for the most part abandoned thimerosal, it is still used in most global health programs. The World Health Organization has consistently underscored that thimerosal is safe, especially considering its important role in vaccine integrity in poor-world settings.

Any change in U.S. policy would have a multiplier effect globally, possibly promoting hesitancy and making supply chains more complex.

ACIP's vote is not law, but it is a strong force behind CDC recommendations and insurance payments. It is not clear if the CDC will ultimately endorse the panel's new recommendation. An official announcement from the agency should come before the beginning of next season's flu season.

The resurgence of the thimerosal controversy is an outgrowth of deeper stresses in America's public health system. It is a fundamental conflict between scientific consensus and ideological disruption. As flu season approaches, experts caution against vigilance, not only against the virus, but against disinformation.

Malaria is still one of the most intractable and deadly diseases, Despite decades of effort, the disease continues to claim nearly 600,000 people annually, with most of the victims being children under the age of five in the poorest parts of the world. Although the advent of vaccines like RTS,S (Mosquirix) and R21 has been an important milestone, the problem of administering multiple doses in resource-poor environments has slowed the world's efforts against malaria. A groundbreaking team at the University of Oxford has now pioneered a game-changing solution: a single-dose malaria vaccine based on microcapsule technology, which has the potential to revolutionize the way we engage with immunization in the world's most vulnerable populations.

In 2023 alone, there were reported cases of 263 million malaria cases globally, and this clearly demonstrates the need to have more efficient prevention methods. The World Health Organization (WHO) has proposed an ambitious goal—90% protection against Plasmodium falciparum (Pf) infection—but present vaccines are not up to the task. Mosquirix, the first WHO-approved malaria vaccine, needs a minimum of three injections and provides only 39% efficacy. R21, created by Oxford and licensed in 2023, enhanced efficacy to 77% with the assistance of Novavax's Matrix-M adjuvant but continues to require two to three doses for maximum protection.

These multi-dose regimens pose a strong obstacle in areas where the healthcare infrastructure is thin. Booster visits are missed, making millions—particularly children—susceptible to infection. Logistical and economic costs of repeated clinic visits, cold chain storage and distribution add to the obstacles to making widespread immunisation.

Published in Science Translational Medicine, the results come at a critical juncture. Malaria remains a devastating epidemic, with more than 263 million cases reported worldwide and close to 600,000 reported deaths in 2023, many of which were in children under five years old. As global health leaders increasingly search for more impactful, scalable solutions, this one-shot vaccine is a bold move toward the World Health Organization's (WHO) ambitious target of 90% protection against Plasmodium falciparum infections.

Despite decades of study and billions spent, malaria is still endemic in more than 90 countries, overwhelmingly impacting the world's poorest regions. One of the longest-standing challenges in combating malaria has been the challenge of keeping vaccination schedules—a particular issue in isolated communities with limited clinic access or refrigeration.

The Oxford microcapsule platform, led by Professor Romain Guyon's team, the new vaccine formulation encloses the malaria antigen in microscopic, biodegradable spheres of PLGA (poly-lactic-co-glycolic acid). The vaccine is administered once, and the microcapsules release a priming dose instantaneously, a subsequent booster dose delivered time-released inside the body, simulating the conventional multi-dose regimen.

"Our microcapsules function like controlled-release vaults," says Guyon. "They deliver the booster on a pre-programmed schedule—two weeks to several months—so the immune system sees a second dose without needing the patient back into the clinic."

This novel timed-release is enabled by chip-based microfluidics technology, enabling researchers to have fine control over capsule size, degradation rate, and release time. Most importantly, the platform can be integrated with standard pharmaceutical manufacturing processes, meaning rapid scaling is both viable and affordable.

In animal models, the one-dose vaccine had 85% efficacy, comparable to that provided by current two-dose regimens. Antibody levels were strong for as long as 11 weeks, and immune response was strong even after refrigeration at 4°C for 4–7 weeks, validating the stability of the vaccine in refrigerated storage conditions.

This holds especially great promise for low-resource environments, where the cold chain—the requirement to keep vaccines at particular temperatures—tends to fail. The microcapsules, at 65 micrometers in diameter, are injectable through regular syringes, with no specialized delivery apparatus.

Dr. Luca Bau of Oxford’s Institute of Biomedical Engineering emphasizes the impact, “Reducing the number of clinic visits could make a major difference in communities where healthcare access is limited. Our goal is to eliminate the structural barriers that prevent people from accessing life-saving innovations.”

As per WHO, 20.5 million children fell behind on routine vaccinations in 2022 alone, many because of logistical challenges a single-dose vaccine would address. Furthermore, malaria disproportionately kills children, and of those deaths, most occur among children younger than age five in sub-Saharan Africa.

Conventional malaria prevention methods—such as insecticide-treated bed nets, anti-malarial drugs, and indoor spraying—have also advanced, but drug resistance and vector adaptation undermine their effectiveness. Vaccines are still the most scalable long-term option, and a single-dose formulation would have the potential to make uptake and outcomes far better.

Although the target now is malaria, scientists indicate the microcapsule technology may be adapted to suit many vaccines and therapies, especially those needing repetitive dosing or complicated regimens. Such vaccines include those for tuberculosis, HPV, as well as future pandemic countermeasures.

Dr. Guyon expounds, "Our technology solves three fundamental problems—programmability, injectability, and scalability. If safe and effective in humans, it has the potential to transform how we administer everything from pediatric vaccines to cancer immunotherapies."

The team is currently gearing up for human clinical trials, the second most important step toward establishing safety and efficacy in diverse populations.