A vaccine advisory group for the World Health Organization said Tuesday that, at this point, it does not recommend additional, let alone annual COVID-19 booster shots for people at low to medium risk of severe disease. It advised countries to focus on boosting those at high risk—including older people, pregnant people, and those with underlying medical conditions—every six to 12 months for the near- to mid-term.

The new advice contrasts with proposed plans by US Food and Drug Administration, which has suggested treating COVID-19 boosters like annual flu shots for the foreseeable future. That is, agency officials have floated the idea of offering updated formulations each fall, possibly to everyone, including the young and healthy.

In a viewpoint published last May in JAMA, the FDA’s top vaccine regulator, Peter Marks, along with FDA Commissioner Robert Califf and Principal Deputy Commissioner Janet Woodcock, argued that annual COVID booster campaigns in the fall, ahead of winter waves of respiratory infections—such as flu, COVID-19, and RSV—would protect health care systems from becoming overwhelmed. And they specifically addressed the possibility of vaccinating those at low risk.

“The benefit of giving additional COVID-19 booster vaccines to otherwise healthy individuals 18 to 50 years of age who have already received primary vaccination and a first booster dose is not likely to have as marked an effect on hospitalization or death as in the other populations at higher risk,” the FDA officials wrote. “However, booster vaccinations could be associated with a reduction in health care utilization (e.g., emergency department or urgent care center visits).”

In a press briefing Tuesday, WHO advisors called the benefit of boosting those at low or even medium risk “actually quite marginal” and suggested that countries could roll back offering primary COVID-19 vaccination series to low-risk healthy children and teens based on country-specific conditions and resources.

Context and limits

These updated recommendations “reflect that much of the population is either vaccinated or previously infected with COVID-19, or both,” said Hanna Nohynek, chair of the WHO’s advisory groups, called SAGE for the Strategic Advisory Group of Experts on Immunization. But the advisor’s updated guidance “reemphasizes the importance of vaccinating those still at risk of severe disease, mostly older adults and those with underlying conditions, including with additional boosters,” she added.

Specifically, the WHO’s SAGE considered high-risk groups: older adults; younger adults with significant comorbidities, such as diabetes and heart disease; people 6 months and older with immunocompromising conditions, such as people living with HIV and transplant recipients; pregnant people; and frontline health workers.

For these high-risk groups, SAGE recommended an additional booster six to 12 months after their last, given the current epidemiological conditions. The advisors noted that the advice is “time-limited” for the current situation, not one for annual or biannual shots to be offered in perpetuity. The scenario and overall recommendations could change depending on new, more virulent variants or future declines in COVID-19 spread, for instance.

Already, the United Kingdom and Canada have offered spring COVID-19 boosters to high-risk groups, including older people and those who have immunocompromising conditions. So far, the FDA has not indicated that it will do the same.

Certain cephalopods like cuttlefish, octopuses, and squid have the ability to camouflage themselves by making themselves transparent and/or changing their coloration. Scientists would like to learn more about the precise mechanisms underlying this unique ability, but it’s not possible to culture squid skin cells in the lab. Researchers at the University of California, Irvine, have discovered a viable solution: replicating the properties of squid skin cells in mammalian (human) cells in the lab. They presented their research at a meeting of the American Chemical Society being held this week in Indianapolis.

“In general, there’s two ways you can achieve transparency,” UC Irvine’s Alon Gorodetsky, who has been fascinated by squid camouflage for the last decade or so, said during a media briefing at the ACS meeting. “One way is by reducing how much light is absorbed—pigment-based coloration, typically. Another way is by changing how light is scattered, typically by modifying differences in the refractive index.” The latter is the focus of his lab’s research.

Squid skin is translucent and features an outer layer of pigment cells called chromatophores that control light absorption. Each chromatophore is attached to muscle fibers that line the skin’s surface, and those fibers, in turn, are connected to a nerve fiber. It’s a simple matter to stimulate those nerves with electrical pulses, causing the muscles to contract. And because the muscles pull in different directions, the cell expands, along with the pigmented areas, which changes the color. When the cell shrinks, so do the pigmented areas.

Underneath the chromatophores, there is a separate layer of iridophores. Unlike the chromatophores, the iridophores aren’t pigment-based but are an example of structural color, similar to the crystals in the wings of a butterfly, except a squid’s iridophores are dynamic rather than static. They can be tuned to reflect different wavelengths of light. A 2012 paper suggested that this dynamically tunable structural color of the iridophores is linked to a neurotransmitter called acetylcholine. The two layers work together to generate the unique optical properties of squid skin.

And then there are leucophores, similar to the iridophores except they scatter the full spectrum of light, such that they appear white. They contain reflectin proteins that typically clump together into nanoparticles, so that light scatters instead of being absorbed or directly transmitted. Leucophores are mostly found in cuttlefish and octopuses, but there are some female squid of the genus Sepioteuthis that have leucophores that they can ‘tune” to only scatter certain wavelengths of light. If the cells allow light through with little scattering, they’ll seem more transparent, while the cells become opaque and more apparent by scattering a lot more light. These are the cells that interest Gorodetsky.

By combing through a collection of data, researchers may have discovered evidence that we’ve already observed the first “blitzar,” a bizarre astronomical event caused by the sudden collapse of an overly massive neutron star. The event is driven by an earlier merger of two neutron stars; this creates an unstable intermediate neutron star, which is kept from collapsing immediately by its rapid spin. In a blitzar, the strong magnetic fields of the neutron star slow down its spin, causing it to collapse into a black hole several hours after the merger.

That collapse suddenly deletes the dynamo powering the magnetic fields, releasing their energy in the form of a fast radio burst. The researchers who performed the analysis suggest that this phenomenon could explain the non-repeating forms of these events.

Too big to live

How big can a neutron star get before it collapses into a black hole? We don’t have a good answer, in part because we’re not sure what happens to the bizarre forms of matter inside one of these massive objects. We don’t even know if the neutrons that give the star its name survive or fall apart into their component quarks. It’s one of those annoying questions where the answer includes the phrase “it depends.”

The big thing it depends on is how fast the neutron star is spinning. A fast enough spin can counteract the pull of gravity on the neutron star’s outer layers, keeping something that’s too heavy to survive around for a bit. If the spin slows down, the whole thing will be rapidly crunched into a singularity. The simplest way to slow one of these stars down is through its magnetic field, which will interact with charged particles in the environment, creating a drag on the object’s spin.

These are the conditions that take a neutron star merger and create a blitzar. If neutron stars are heavy enough, their merger will create an object that’s above the mass limit that should cause it to collapse into a black hole. But the collision is also likely to set the object spinning fast enough that it cannot collapse. Their churning, superfluid interiors can also host a dynamo that supports an intense magnetic field, potentially making the object a magnetar but definitely slowing its spin. The dynamics of this balance are such that the blitzar should occur within hours of the neutron star merger.

Once the collapse happens, the dynamo that created the magnetic fields vanishes along with the rest of the neutron star. There’s a lot of energy wrapped up in that field, and the loss of the neutron star releases it in a process that the new paper refers to as “shedding the magnetosphere.” That burst of energy is something we can potentially detect.