Viruses are constantly evolving and changing. Every time a virus replicates (makes copies of itself), there is the potential for there to be changes in its structure. Each of these changes is a “mutation.” A virus with one or more mutations is called a “variant” of the original virus.
Some mutations can lead to changes in important characteristics of the virus, including characteristics that affect its ability to spread and/or its ability to cause more severe illness and death.
Omicron and its subvariants have ranked as the predominant SARS-CoV-2 strains in the U.S. for almost two years now. While the original Omicron strain (BA.1) is no longer circulating, Omicron subvariants are now driving most of the country’s SARS-CoV-2 infections. Omicron was first identified in Botswana and South Africa in late November 2021, and cases quickly began to surface and multiply in other countries. By December of that year, Omicron was causing daily case numbers in the U.S. to skyrocket to over a million. In 2022, it had spawned a number of subvariants. In 2023, a new Omicron strain called EG.5 (nicknamed “Eris”) is the dominant strain in the U.S., and experts are monitoring another new strain called BA.2.86 (nicknamed “Pirola”).
How contagious is it? Omicron’s subvariants are considered to be especially efficient spreaders of the disease. The original strain of Omicron was more transmissible than Delta was. One explanation was that more than 30 of Omicron’s mutations are on the virus’s spike protein, the part that attaches to human cells, and several of those are believed to increase the probability of infection.
Severity: Scientists are still working to learn more about whether the current Omicron strains cause more severe disease than their predecessors. Data has suggested that the original Omicron strain was less severe, in general, than previous variants, according to the CDC. But it has also been noted that surges in cases may lead to significant increases in hospitalizations and deaths, as they did during the variant’s spread at the beginning of 2022, when the estimated death rates went as high or higher than they were at the time of the Delta variant surge in the previous autumn.
Can vaccination prevent it? The CDC says that while breakthrough infections in vaccinated people are expected, staying up to date with vaccinations is the best protection against Omicron. Scientists are evaluating the effectiveness of a new fall 2023 updated COVID-19 booster against EG.5 and BA.2.86, according to the CDC. Currently, the CDC says the updated vaccine is expected to be effective at reducing severe disease and hospitalization from the two recent subvariants.
Delta (B.1.617.2) was first identified in India in late 2020; it soon spread throughout the world, becoming what was the predominant version of the coronavirus—until Omicron took its place in mid-December of 2021.
How contagious is it? It’s estimated that Delta caused more than twice as many infections as previous variants—in Connecticut, it was estimated to have been 80 to 90% more transmissible than the Alpha variant. In the U.S., in June 2021, after a steady decline in COVID-19 cases and hospitalizations, the arrival of Delta coincided with a rapid reversal of that trend. In the fall of 2021, there were surges even in the most vaccinated states, prompting experts to urge people to get their booster shots.
Severity: Delta caused more severe disease than other variants in people who weren’t vaccinated. Early studies from Scotland and Canada, both cited by the CDC, suggested Delta was more likely to result in hospitalization in the unvaccinated. A report in the Lancet found that people in England had double the hospitalization risk with Delta than they did with Alpha, the previously dominant variant in that country.
Can vaccination prevent it? All three vaccines in the U.S. were considered highly effective against severe illness, hospitalizations, and death from Delta. No vaccine is 100% effective, and Delta caused breakthrough infections in some fully vaccinated people. Also, infected vaccinated people could spread the virus to others, although likely they were infectious for a shorter time.
Delta also prompted the CDC to recommend “layered prevention strategies” for both the vaccinated and the unvaccinated. That means that, in addition to staying up-to-date with their vaccines, people were advised to practice such strategies as washing hands, wearing masks, and maintaining a physical distance from one another, especially when indoors in places where there was substantial or high transmission.
This variant, or B.1.351, was identified in South Africa at the end of 2020 and spread to other countries. Experts had been concerned about its several mutations and its potential to evade antibodies. Beta was not common in the U.S.
How contagious is it? The CDC said Beta was about 50% more contagious than the original coronavirus strain.
Severity: There was evidence to suggest that Beta may have been more likely than other variants to lead to hospitalization and death.
Can vaccination prevent it? South Africa stopped offering the AstraZeneca-Oxford vaccine (which is not available in the U.S.) early in 2021 after clinical trials showed it did not provide strong protection against mild and moderate disease from the Beta variant. Pfizer-BioNTech, Moderna, and Johnson & Johnson also reported less protection against Beta.
Alpha (B.1.1.7) was the first of the highly publicized variants. Alpha first appeared in Great Britain in November 2020 and infections surged in December of that year. It soon surfaced around the world and became the dominant variant in the U.S., where the CDC classified it as a variant of concern. Then, Alpha faded away with the rise of the more aggressive Delta variant.
How contagious is it? Some mutations in Alpha’s spike protein were thought to make it more infectious. The B.1.1.7 lineage was believed to be 30 to 50% more contagious than the original SARS-CoV-2 strain. In the U.S., in mid-April 2021—before Delta became predominant—Alpha comprised 66% of cases, according to a study released in June by the CDC.
Severity: Studies have suggested the B.1.1.7 lineage was more likely to land infected people in the hospital and was deadlier than the original virus.
Can vaccinations prevent it? Pfizer, Moderna, and Johnson & Johnson all said their vaccines were effective in preventing severe disease and hospitalization in Alpha cases.
This article was medically reviewed by Yale School of Public Health epidemiologist Nathan Grubaugh, PhD.
Note: Information provided in Yale Medicine articles is for general informational purposes only. No content in the articles should ever be used as a substitute for medical advice from your doctor or other qualified clinician. Always seek the individual advice of your health care provider with any questions you have regarding a medical condition.
Vaccines prepare a person’s immune system (the body’s natural defenses) to recognize a particular disease and defend against it.
Scientists are working on several types of vaccines against COVID-19, using different technologies.
The EU portfolio currently includes vaccines based on four different technologies:
mRNA (uses part of the genetic code of the coronavirus)
vaccines based on a viral vector (a genetically modified virus is a carrier of part of the DNA of the coronavirus)
protein-based vaccines (contain fragments of a protein that is unique to the coronavirus)
vaccines with inactivated virus (made from live virus by chemical inactivation)
vaccine mRNA
The mRNA molecule is naturally used by our body as a guide for the creation of all the proteins we need. Scientists have built on decades of research into mRNA to use as a basis for vaccine development.
While researching the coronavirus, scientists discovered a protein, the so-called spike protein that allows it to enter human cells and infect them. They artificially created instructions for the creation of this protein, the so-called messenger RNA, or mRNA. These instructions are a key component of the vaccine.
This is a new approach to vaccines, as they contain no part of the virus, just instructions for your cells to make a protein similar to the coronavirus protein, triggering an immune response and equipping you with the resources to defeat the real virus.
Pfizer/BioNTech and Moderna vaccines against COVID-19, which use mRNA technology, have been approved in the EU.
Vaccines based on viral vector
Viral vector-based vaccines use a harmless virus to deliver instructions from the coronavirus into our bodies to make a protein unique to the COVID-19 virus and thereby trigger an immune response.
The EU-licensed COVID-19 vaccines from AstraZeneca and Janssen are viral vector-based vaccines. The Sputnik V vaccine, which is currently under continuous review by the EMA, is also a vaccine based on a viral vector.
An important advantage of viral vector-based vaccines is that they are very durable and can be stored at room temperature in a refrigerator for up to six months. Another advantage of the Janssen vaccine is that one dose is sufficient to achieve immunity against the virus.
Protein-based vaccines
This type of vaccine contains fragments of a protein that is unique to this virus.
This is enough for the immune system to recognize that this unique protein should not be present in the body and respond by launching a natural defense response against the infection of COVID-19.
The first protein-based vaccine to be approved for use in the EU is the vaccine produced by Novavax. The Sanofi/GSK vaccine, which is authorized for use in the EU, is also a protein-based vaccine.
Vaccines with inactivated virus
This type of vaccine contains parts of the actual COVID-19 virus that has been inactivated in the laboratory to destroy its ability to cause disease.
When the immune system comes into contact with the inactivated virus, it responds by creating a natural defense against the infection of COVID-19.
Valneva’s vaccine, which is authorized for use in the EU, is an inactivated virus vaccine.
All viruses, including SARS-CoV-2, the virus that causes COVID-19, change over time. Most changes have little to no impact on the virus’s properties. However, some changes may affect the virus’s properties, such as how easily it spreads, the associated disease severity, or the performance of vaccines, therapeutic medicines, diagnostic tools, or other public health and social measures.
In June 2020, the WHO Virus Evolution Working Group was established with a specific focus on SARS-CoV-2 variants, their phenotype and their impact on countermeasures. This later became the Technical Advisory Group on SARS-CoV-2 Virus Evolution. In late 2020, the emergence of variants that posed an increased risk to global public health prompted WHO to characterize some as variants of interest (VOIs) and variants of concern (VOCs) in order to prioritize global monitoring and research, and to inform and adjust the COVID-19 response. From May 2021 onwards, WHO began assigning simple, easy-to-say labels for key variants.
Considerable progress has been made in establishing and strengthening a global system to detect signals of potential VOIs or VOCs and rapidly assess the risk posed by SARS-CoV-2 variants to public health. It remains critical that these systems are maintained, and data are shared, according to good principles and in a timely fashion, as SARS-CoV-2 continues to circulate at high levels around the world. While monitoring the circulation of SARS-CoV-2 globally, it also remains essential to monitor their spread in animal populations and chronically infected individuals, which are crucial aspects of the global strategy to reduce the occurrence of mutations that have negative public health implications. In March 2023, WHO updated its tracking system and working definitions for variants of concern, variants of interest and variants under monitoring. They can be found here. The previous working definitions can be found here.
Nearly four years after COVID-19 emerged, public health experts already say it’s not a matter of if we’ll have another pandemic — but when. So Yahoo Life asked several experts for their take on where the next pandemic could come from. Here’s what they said.
Viruses
Experts point to a virus as the most likely source of the next pandemic — and for good reason: Most modern pandemics have come from viruses, and there are plenty of types of viruses that could be responsible for the next one.
“My sense is that the next pandemic will also be a viral pathogen transmitted by the respiratory route (rather than fecal/oral or by contact), mainly since the airborne/respiratory route is more efficient,” Dr. Dean Winslow, a professor of infectious diseases at Stanford University School of Medicine says in an email to Yahoo Life. “Either a coronavirus, influenza or parainfluenza virus variants would be good bets.”
A likely reservoir for viruses with pandemic-level potential is animals, and as humans encroach further on animals’s habitats through deforestation, there will be more opportunities for animal viruses to adapt to human hosts.
We’ve already seen plenty of examples of viruses making the jump from animals to humans: Middle East respiratory syndrome (MERS) originated in camels; severe acute respiratory syndrome (SARS) originated in small mammals; HIV originated in chimpanzees; and one COVID-19 theory suggests the disease may have originated in racoon dogs.
“Influenza viruses use birds as their natural reservoir, and certain strains have become adapted to transmission and infection of mammals (especially pigs and humans),” Winslow says. “Similarly, coronaviruses have been known to primarily use bats as their primary reservoir, but with SARS-CoV-2 we saw extensive transmission between other species including humans, deer and both wild and domestic cats.”
Some experts say the next pandemic is most likely to emerge from a virus originating in bats — which have the highest proportion of zoonotic viruses among mammals — rodents or birds.
But what kind of virus could it be? Experts say there are a few probable culprits, including:
Influenza viruses: You’re likely familiar with the seasonal flu, but in the last century there have also been four influenza pandemics: the infamous Spanish Flu pandemic in 1918, the H2N2 flu pandemic in 1957, the H3N2 flu pandemic in 1968 and the H1N1 flu pandemic 2009. Dr. Allen Cheng, director of infectious diseases at Monash Health, writes that influenza isn’t as infectious as other respiratory infections, but its short incubation period means outbreaks can spread quickly. Dr. Wafaa El-Sadr, an epidemiology professor at Columbia University Mailman School of Public Health, tells Yahoo Life: “There’s concern about influenza and whether a new strain of influenza could arise that could be deadly and could create an outbreak around the world, if not a pandemic.”
Coronaviruses: These respiratory viruses are responsible for the COVID-19 pandemic as well as other diseases including MERS, which was first reported in 2012, and SARS, which caused a global outbreak in 2003.
New viruses: “There are some viruses that we haven’t even detected or that we don’t know have a pandemic potential,” Pablo Penaloza-MacMaster, an assistant professor of microbiology and immunology at Northwestern University Feinberg School of Medicine, tells Yahoo Life. “So we have to keep an open mind.” El-Sadr explains that “new viruses” could also mean pathogens that already exist in animals but haven’t been identified in humans before.
Bacteria
Cholera (caused by Vibrio cholerae bacteria) and bubonic plague, or the Black Death (caused by the bacterium Yersinia pestis) are some of the most famous examples of how devastating a pandemic can be. But experts say that today we’re unlikely to see pandemics on that scale caused by bacteria.
“If you go back to the 1300s, we did not have very good infrastructure and very good sanitation measures,” Penaloza says. “Right now, assuming that you have a population with access to clean water and there’s good hygienic measures, then you raise the bar. You have to have a pathogen that has the ability of transmitting in a setting where people wash their hands and have proper sanitation measures — and I think viruses are more likely to cross that threshold than other pathogens [like bacteria].”
El-Sadr says that, in general, “most people would believe that it’s likely to be a virus, rather than a bacterium, but at the same time it doesn’t mean that it’s impossible that a bacterium will be the cause of a pandemic. We’re seeing [antibiotic-resistant] bacteria around the world, in almost every country around the world. And that’s causing a lot of disease and mortality as well.”
Antimicrobial resistance — or when germs like bacteria and fungi develop the ability to defeat the drugs designed to kill them — is considered “an urgent global public health threat,” with at least 1.27 million deaths attributed to antimicrobial resistance in 2019.
But El-Sadr points out that right now antimicrobial resistance is mostly restricted to hospital and health care facility settings.
Fungi
Dr. Andrej Spec, who specializes in fungal infections as associate director of the infectious disease clinical research unit at Washington University School of Medicine in St. Louis, previously told Yahoo News that fungi pose a major health threat but are chronically misunderstood.
“It’s quite likely that we’ll have an emergence of a new fungus that may, in the next 20 years, be responsible for a couple hundred thousand deaths a year,” Spec said.
“And you know, we already have many fungi that cause a couple 100,000 deaths a year — we just ignore them, because we have this narrative that fungi are rare,” he added.
The World Health Organization released its first ever list of fungal priority pathogens last year in response to the increased threat of invasive fungal disease. Candida auris, for example, was first discovered in humans in 2009, and since then hundreds of thousands of cases have been identified in countries around the world, including in the U.S. It’s highly drug-resistant and fatal in one-third of patients, and was likely able to adapt to infect humans thanks to rising temperatures due to global warming.
But Spec thinks it’s unlikely we’ll see a fungal pandemic at the scale of the COVID-19 pandemic, where a single virus was responsible for millions of deaths worldwide.
“The fact is, it hasn’t happened ever, so it’s very unlikely to actually happen,” he says.
Penaloza says that a biological advantage viruses and bacteria have over fungi is that they replicate much faster — enabling them to spread more easily.
“It depends on the virus, of course, but with a virus you can have millions of copies in one day. With fungi, it doesn’t replicate at those high levels, and the mutation rate of fungi is not as high as viruses,” Penaloza explains.
That said, “It could still happen,” he says. “We shouldn’t rule it out, but I think statistically speaking it’s more likely that [the next pandemic] is going to be a virus. Maybe bacteria, but I think my bet is on viruses more.”
Individual variants of the coronavirus are divided in the so-called VOI/VOC classification into:
Variants of interest (Variant of Interest, VOI)
A variant with specific genetic markers that have been associated with changes in receptor binding, reduced levels of neutralizing antibodies produced by previous infection or after vaccination, reduced treatment efficacy, potential diagnostic impact, or predicted increases in transmissibility or disease severity.
Variants of Concern (VOC)
A variant in which there is evidence of increased transmission, a more severe disease course (eg, increased hospitalizations or deaths), a significant reduction in neutralizing antibodies generated during a previous infection or vaccination, reduced efficacy of treatment or vaccines, or failure of diagnostic detection.
Monitored variants (Variants under monitoring, VUM)
These SARS-CoV-2 virus variants were detected through epidemic intelligence and genomic variant screening or preliminary scientific evidence. The variants classified under VUM could have properties similar to those of VOCs, but it is necessary to monitor them further. The variants listed here must be present in at least one community-detected outbreak within the EU/EEA, or there must be evidence that there is community transmission of the variant elsewhere in the world.
De-escalated varianty
According to the ECDC, some variants are now so-called de-escalated, i.e. they are removed from the VOI/VOC classification system, for example variants and sub-variants alpha, beta, gamma, epsilon, delta, kappa, eta, theta, zeta and others.
What can be done to limit the spread of the virus?
In order to limit the spread of the virus that causes the disease COVID-19 and to protect public health, the consistent and increased enforcement of strategies such as vaccination, physical distancing, the use of respirators especially in healthcare facilities, in social care institutions and in the case of symptoms of respiratory disease, hygiene hand and other relevant anti-epidemic measures based on risk assessment.
Some variants of the coronavirus appear and disappear during the pandemic, other variants are more successful, persist and spread in the population.
So far, several significant variants of the SARS-CoV-2 virus have been documented worldwide since the beginning of the covid-19 pandemic. In May 2021, the World Health Organization (WHO) recommended that the Greek alphabet be used to name the different variants of the coronavirus, in the order in which individual mutations were detected. For example, Alpha, originally a British variant, called B.1.1.7, was identified in the United Kingdom (UK) in September 2020, Beta, originally a South African variant, called B.1.351 appeared in South Africa independently of B.1.1.7 . in September 2020, Gamma, originally a Brazilian variant, called P.1, appeared in December 2020 in Brazil, Delta, originally an Indian variant, called B.1.617.2, was first identified in December 2020 and showed increased infectivity, Omikron, called B.1.1.529, was identified at the beginning of November 2021. This variant of the SARS-CoV-2 virus belonging to the Pango lineage B.1.1.529 is characterized by a high number of mutations in the S-gene compared to the original virus. The “Centaurus” variant (“Centaur”, which is only a working name) called BA.2.75 is a sub-variant of Omicron and was first captured in May 2022 in India. The Centaur variant has some structural and genetic changes in the spike protein. We don’t yet know if it will bypass our immune defenses or cause serious illness.