What Will It Take to Stop the Delta Variant?
(Bloomberg) -- A more powerful driver of Covid-19 outbreaks than any strain of the coronavirus encountered so far, the delta variant is testing the limits of public health defenses globally. The good news is that in most cases, the effectiveness of vaccines at protecting against severe disease is maintained; the vast majority of infections are occurring in unvaccinated people. But vaccines alone don’t provide a fail-safe shield. Increasingly, public health specialists stress that countering delta will require multiple strategies.
1. Why is delta harder to stop than other strains?
- It replicates faster and reaches significantly higher concentrations in the upper airways.
- It’s expelled in greater quantities by infected individuals.
- Its viral particles are better at latching on to the ACE2 receptor, an enzyme found on the surface of many cells that the virus uses to infect them.
- It may be more efficient at causing infection, by requiring fewer viral particles or a lower infectious dose.
2. What’s the best defense against delta?
A full course of vaccination, which is two shots for most formulations, is the best way to protect against sickness requiring hospitalization in the event of a delta infection. To quash delta’s threat, it’s necessary that sufficient supplies of vaccine are made available worldwide, and that sizable majorities in communities get inoculated. Without that, populations will be susceptible to delta-driven epidemics that will result in large numbers of infections, hospitalizations, and, ultimately, deaths. Where that occurs, eventually enough of those who survive will develop natural immunity to reduce the number of people susceptible to the virus, causing transmission to slow and eventually stop. Allowing that to happen would not only create misery in the community and burnout among health-care workers, it would also risk spawning new variants. The more the virus circulates, the more opportunity it has to acquire mutations that enable it to evade immunity or transmit even more readily.
3. Are vaccines working?
Yes. The benefit of immunization is that it trains the immune system to recognize and fight the virus faster, which helps prevent an infection from progressing. So an infection that might otherwise have caused severe illness is more likely to result in a mild case, and what could have been a mild case may instead be an asymptomatic infection. Countries with high rates of immunization have a lower proportion of Covid cases requiring hospitalization, providing proof that vaccines are working.
4. Then why are infections occurring among the vaccinated?
No Covid vaccine provides complete protection against infection. Antibodies trained to block or neutralize the coronavirus are the key defense against stopping infection and preventing onward transmission. But people react differently to vaccination, resulting in a wide variation in the amount and quality of the antibodies they generate after an inoculation. Research suggests that some vaccinated individuals may not produce sufficient antibody levels in their upper airways to counter a delta infection early enough to stop it from replicating in the nose and throat, leading to so-called breakthrough infections. Still, a fully vaccinated person typically clears the infection faster than someone who’s unvaccinated or partially vaccinated. That not only prevents the infection from causing worse symptoms, it also shortens the period a vaccinated person is likely to be infectious and thus reduces their likelihood of passing the virus on.
5. What can be done to make vaccines more effective?
Health authorities in some wealthy countries have begun offering additional doses to bolster levels of immunity -- a third shot in the case of most vaccines or a second one in the case of the single-dose Johnson & Johnson formulation. Such decisions may be based on concerns about the effectiveness of the shots already used, waning levels of immunity over time, and the need to protect especially vulnerable groups, notably the elderly and people with underlying immune deficiencies that prevented them from gaining the level of protection that a regular course of vaccine provides people with normal immune systems. In time, periodic booster doses of vaccine will likely be needed for everyone to strengthen and broaden their array of virus-blocking antibodies. Studies so far indicate immunity is enhanced when different types of vaccines are used in combination. Offering extra doses now, however, is controversial. Some public health specialists have characterized it as unethical as long as poorer countries lack supplies to cover significant portions of their populations with initial shots.
6. Are vaccines enough?
Health professionals say vaccines won’t be sufficient to stop delta in communities with high rates of transmission. Where that’s the case, they say, additional measures will be necessary to impede its spread. These include the same strategies that were central before vaccines became available: people wearing face masks, maintaining a physical distance from others, and avoiding mass gatherings, such as summer festivities on Cape Cod that resulted in a large outbreak among mostly vaccinated people. In addition, researchers are calling for ventilation systems to be overhauled just as public water supplies were in the 1800s after fetid pipes were found to harbor cholera. In an article in the journal Science, 39 scientists from 14 countries asked the World Health Organization to extend its indoor air quality guidelines to cover airborne pathogens such as the coronavirus, and for building ventilation standards to include higher airflow, filtration and disinfection rates as well as monitors that enable members of the public to gauge the quality of the air they’re breathing.
7. Will vaccines ever be able to prevent coronavirus infection?
Potentially. The shots we’re using now may not be the ones we rely on in the future. Among the Covid vaccines under development are some that aim to stimulate a more robust immune response in the nasal tract through which the virus is likely to enter the body. The hope is that by improving immune defenses there, the virus could be snuffed out before it has a chance to cause an infection, much less penetrate the lungs and cause a more severe illness.
The Reference Shelf
- Related QuickTakes on why delta is so disruptive, the future of Covid, the debate over booster shots, breakthrough infections, and how well vaccines are working.
- The World Health Organization’s weekly epidemiological update on Covid-19.
- The Centers for Disease Control and Prevention explains what you need to know about SARS-CoV-2 variants.
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