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Newer variants of the coronavirus, such as Alpha and Delta, are highly contagious and infect many more people than the original virus. Two new studies offer a possible explanation: The virus is evolving to spread more efficiently through the air.
realizing that coronavirus spreads indoors Transforming efforts to contain the pandemic last year, it sparked heated debates about masks, social distancing and ventilation in public spaces.
Most researchers now agree that coronavirus is mostly transmitted through large droplets that settle quickly to the ground and much smaller droplets called aerosols, which can float indoors for longer distances and lodge directly in the lungs, where the virus is most harmful.
Recent studies do not fundamentally change this view. But the findings point to the need for better masks in some cases, suggesting that the virus has changed in a way that makes it more challenging.
“This is not an Armageddon scenario,” said Vincent Munster, a virologist with the National Institute of Allergy and Infectious Diseases, who led one of the new studies. “It’s like a modification of the virus for more efficient transmission, something I think we’ve all been waiting for, and now we’re seeing it happening in real time.”
Dr. Munster’s team showed that small aerosols travel much longer distances than larger droplets and the Alpha variant. was much more likely to cause new infections via aerosol delivery. The second study found that people were infected with Alpha. inhaled about 43 times more virus converted into smaller aerosols than those infected with older variants.
Studies have compared the Alpha variant with the original virus or other older variants. But the results may also explain why the Delta variant is so contagious and has replaced all other versions of the virus.
“This really shows that the virus has evolved to become more efficient at airborne transmission,” said Linsey Marr, an airborne virus specialist at Virginia Tech, who was not involved in either study. “I wouldn’t be surprised if that factor was even higher with Delta.”
The ultratransmissibility of variants may depend on a number of factors. It may be that lower doses of the variants are required for infection, or that variants replicate more rapidly, or that more of the variant virus is inhaled into aerosols or all three.
The alpha variant has proven to be twice as contagious as the original virus, and the Delta variant has mutations that further accelerate its infectivity. As the virus continues to change, newer variants may become even more contagious, experts said.
But the tools at our disposal still work well to stop the spread. Even loose-fitting cloths and surgical masks block about half of the fine aerosols containing the virus, according to research on people infected with the variants, published this month in the journal Clinical Infectious Diseases.
Still, Don Milton, an aerosol expert at the University of Maryland who led the research, said at least in some crowded areas, people may want to consider switching to more protective masks.
Dr. “Considering that it has evolved to produce better aerosols, we need better containment and better personal protection,” Milton said of the virus. “We recommend that people switch to more tight-fitting masks.”
To compare how different variants spread through the air, his team had participants with mild or asymptomatic infections read the alphabet, sing “Happy Birthday” out loud, or ask the University of Maryland’s “Go Terps!” He asked them to shout the slogan.
People infected with the alpha variant had much greater amounts of the virus in their noses and throats than those infected with the original virus. But even after adjusting for this difference, those infected with the variant released about 18 times more virus into the smallest aerosols.
However, the researchers studied only four people infected with Alpha and 45 with older variants. This could skew the observed differences between variants, said Seema Lakdawala, a respiratory virus specialist at the University of Pittsburgh, who was not involved in either new study.
Infected people can transmit the virus to many or no one. How much virus they spread may depend on where in their respiratory tract it multiplies, the nature of the surrounding mucus, and what other microbes it can travel with.
State of Vaccination Duty in the USA
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- vaccination rules. On August 23, the FDA Pfizer-BioNTech’s coronavirus vaccine granted full approval For people aged 16 and over, paving the way for entitlements in both countries public and special sectors. Such powers legally allowed and upheld in court appeals.
- Colleges and universities. More than 400 colleges and universities require their students to be vaccinated against Covid-19. Nearly all in states that voted for President Biden.
- Schools. California It was the first state to Vaccination mandatory for all educators and announced plans to add the Covid-19 vaccine as follows: obligation to go to school as early as next fall. Los Angeles There is already a vaccination requirement for students aged 12 and over who attend the class in person from 21 November. New York City has introduced a vaccination requirement for teachers and staff, but it has not yet been enacted due to legal challenges. On September 27, a federal appeals panel reversed a decision temporarily suspended this mission.
- Hospitals and medical centers. Many hospitals and major healthcare systems It wants employees to be vaccinated. Duties for healthcare workers in Turkey California and New York State It apparently forced thousands of people to take the shot.
- New York City. Proof of vaccination is required for workers and customers. indoor dining, gyms, performances and other indoor situations. City training staff and hospital staff It also needs to be vaccinated.
- at the federal level. on September 9, President Biden has declared a mandate for the vaccine. the vast majority of federal workers. This authorization will apply to the employees of the company. Management DepartmentIncluding the White House and all federal agencies and members of the armed forces.
- tIt’s the private sector. Mr. Biden made it mandatory. All companies with more than 100 employees Require vaccination or weekly testing helps advance new institutional vaccination policies. Some companies, for example United Airlines and Tyson Foods, before Mr. Biden’s announcement, he had powers.
Dr. “We have no idea why some individuals are super spreaders and others are not,” Lakdawala said. “There is a lot of heterogeneity among individuals.”
Data from a larger number of participants would have been more convincing, but the two studies together suggested that enhanced transport via aerosols contributes, at least in part, to the infectivity of the variant.
Dr. Munster’s study involved Syrian hamsters, not humans. Dr. Using animals allowed the team to tightly control the experimental conditions and focus solely on the movement of aerosols, Munster said.
The researchers separated the hamster pairs with tubes of different lengths that allowed airflow but no physical contact. They looked at how well different variants traveled, from infected “donor” hamsters to uninfected “sentry” hamsters.
Only the smallest aerosols – particles smaller than 5 microns – have been shown to infect sentry hamsters when the distance between cages is more than two meters. And the team found that, as expected, the Alpha variant outperformed the original virus in infecting sentinel hamsters.
The results were published on bioRxiv, a website that includes articles before they are published in a scientific journal.
Dr. Munster said the researchers are now testing the Delta variant and expect to find it more efficient.
Experts said that the new findings underline the importance of masks for people vaccinated together, especially in crowded areas. Although people with immediate infections after vaccination are much less likely to spread the virus than those who have not been vaccinated, variants are more likely to be contagious.
With billions of people worldwide vaccinated and billions still unvaccinated, the virus could change in unexpected ways, said Dr. Munster: “There may be additional evolutionary pressures shaping the evolutionary direction of this virus.”
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