After a period of falling Covid-19 illness rates, the recent spread of the delta variant of SARS-CoV-2 was a major disappointment and necessitated a reexamination of some previous assumptions. This reconsideration may, at least in part, be a correction to overly optimistic views of what highly effective SARS-CoV-2 vaccines could accomplish. Some observers had hoped the vaccines could eliminate transmission of the virus, the ultimate goal of reaching herd immunity.1 A more likely picture of our future with this virus comes into focus if we examine the well-known infection patterns of another respiratory virus, influenza, both in and outside pandemics. That experience can help us reset expectations and modify goals for dealing with SARS-CoV-2 as it further adapts in global spread.
Early results from the clinical trials and observational studies of mRNA vaccines against SARS-CoV-2 indicated that not only were they highly effective at preventing symptomatic infection, but they were also effective in preventing asymptomatic infection and therefore transmission.2 The basic criterion used for emergency use authorization by the Food and Drug Administration was a standard one: prevention of laboratory-confirmed clinical infection meeting a case definition. The effect on asymptomatic infections was a welcome surprise, because it has been thought that most vaccines for respiratory illnesses, including influenza, are “leaky” — that is, they allow some degree of asymptomatic infection and are better at preventing symptomatic infection.
The initial data on inapparent SARS-CoV-2 infection strengthened the hope that, at a certain level of vaccination, transmission would cease completely. To many of us, this hope appeared overly optimistic, and it seems even more so now; the highly transmissible delta variant causes asymptomatic infections and sometimes illnesses (albeit usually mild) in vaccinated people, probably because of increased growth potential, as well as because of waning immunity, which also involves decreasing IgA antibody levels. Elimination of an illness by means of herd immunity works best when the agent has low transmissibility, and it requires the absence of pockets of susceptible people. Eliminating Covid-19 seemed theoretically possible, because the original 2002 SARS virus ultimately disappeared. That virus, however, did not transmit as well as even the initial strain of SARS-CoV-2. It occurred in limited regions and was characterized by focal spread, including superspreading events. Such a pattern, which was also seen in the early days of SARS-CoV-2, is called “overdispersion” — 10% of cases, for example, may be responsible for 80% of transmission.3 These dynamics explain why there were great differences in antibody prevalence within a given city and spotty global spread early in the pandemic. Overdispersion was thought to be an unstable trait that would disappear, with transmission becoming more uniform and higher overall. That transition appears to have occurred as newer variants take over.
Given the parade of variants, their varying transmissibility, and continuing concern about antigenic changes affecting vaccine protection, I believe it should now be clear that it is not possible to eliminate this virus from the population and that we should develop long-term plans for dealing with it after the unsupportable surges are fully controlled. Pandemic and seasonal influenza provide the most appropriate models to aid in developing strategies going forward.
As with SARS-CoV-2, when a novel pandemic influenza strain appears, its spread can overwhelm the health care system. Waves of infection go through a city in weeks and a country in months, but there is scant evidence that superspreading events occur. Thereafter, the pandemic virus persists as a new seasonal strain, and antigenic changes occur — albeit probably not as quickly as we are seeing with SARS-CoV-2. The new strain joins the other seasonal influenza types and subtypes that reappear each year. The goal of vaccination becomes managing the inevitable outbreaks and reducing the rates of moderate-to-severe illness and death. Preventing mild disease, though important, is less critical.
Readministration of influenza vaccine has become an annual event for much of the population, in response to both waning immunity and the appearance of variants, termed antigenic drift, necessitating updated vaccines. Even when there is no substantial drift, revaccination is recommended because of waning immunity. But antigenic drift is a constant issue and is monitored globally, with vaccine composition updated globally twice a year on the basis of recommendations from a World Health Organization consultation.4 As outlined in the table, various criteria are considered in decisions about which strains to include in vaccines. Vaccine effectiveness against laboratory-confirmed symptomatic infection is never higher than 50 to 60%, and in some years it is much lower. Thus, the value of influenza vaccines, now given to as many as 70% of people in some age groups, lies not in eliminating outbreaks but in reducing them and preventing severe complications.
Though there may be similarities between SARS-CoV-2 and influenza, there are also meaningful differences. The most obvious difference is the efficacy of SARS-CoV-2 vaccines, which is currently much higher than we can achieve with influenza vaccines. Whether that degree of efficacy will continue is one of the many open questions that can only be answered over time. It is clear, however, that revaccination will be necessary, for the same reasons that influenza revaccination is necessary: antigenic variation and waning immunity. Data on the frequency of reinfection with seasonal coronaviruses may not be relevant, but they suggest that protection is relatively short term even after natural infection.5 Revaccination frequency and consequences will need to be determined.
Let us hope that certain problems with the influenza vaccine — such as the failure of vaccination, in some years, to produce the desired increase in protection in previously vaccinated people — do not occur with the SARS-CoV-2 vaccines. Other issues, such as the variant to be targeted by vaccines, will need to be addressed. The successful public–private collaboration in selecting influenza strains offers a model for dealing with such issues. SARS-CoV-2 vaccines will be used globally, and the strain or strains contained in future vaccines will need to be chosen globally, in consultation with the manufacturers.
Most predictions about the shape of the post–Covid-19 world have been inaccurate — a reflection of rapid changes in knowledge. But we can now see a picture emerging in which use of effective vaccines will continue to be critical over the long term. Increases in asymptomatic infections and mild illnesses in vaccinated people will nonetheless continue to be possible, as variants continue to emerge. Counts of hospitalizations and deaths may be more important in monitoring the overall impact than numbers of cases, as long as the vaccines continue to be largely effective at preventing severe illness. The possibility of severe illnesses in a small proportion of vaccinated people does emphasize one of the greatest unmet needs we currently face: continued emphasis on better therapeutics and antiviral agents, which will not be affected by molecular changes in the virus as much as vaccines are….
![](https://www.nanoappsmedical.com/wp-content/uploads/2017/05/spacer.jpg)
News
Breakthrough in Antimicrobial Technology with Cinnamon-Based Nanokiller
The need for innovative antimicrobial agents has become increasingly urgent due to the rise of antibiotic-resistant pathogens and the persistent threat of infections acquired during hospital stays. Traditional antibiotics and antiseptics are often ineffective [...]
The Silent Battle Within: How Your Organs Choose Between Mom and Dad’s Genes
Research reveals that selective expression of maternal or paternal X chromosomes varies by organ, driven by cellular competition. A new study published today (July 26) in Nature Genetics by the Lymphoid Development Group at the MRC [...]
Study identifies genes increasing risk of severe COVID-19
Whether or not a person becomes seriously ill with COVID-19 depends, among other things, on genetic factors. With this in mind, researchers from the University Hospital Bonn (UKB) and the University of Bonn, in [...]
Small regions of the brain can take micro-naps while the rest of the brain is awake and vice versa
Sleep and wake: They're totally distinct states of being that define the boundaries of our daily lives. For years, scientists have measured the difference between these instinctual brain processes by observing brain waves, with [...]
Redefining Consciousness: Small Regions of the Brain Can Take Micro-Naps While the Rest of the Brain Is Awake
The study broadly reveals how fast brain waves, previously overlooked, establish fundamental patterns of sleep and wakefulness. Scientists have developed a new method to analyze sleep and wake states by detecting ultra-fast neuronal activity [...]
AI Reveals Health Secrets Through Facial Temperature Mapping
Researchers have found that different facial temperatures correlate with chronic illnesses like diabetes and high blood pressure, and these can be detected using AI with thermal cameras. They highlight the potential of this technology [...]
Breakthrough in aging research: Blocking IL-11 extends lifespan and improves health in mice
In a recent study published in the journal Nature, a team of researchers used murine models and various pharmacological and genetic approaches to examine whether pro-inflammatory signaling involving interleukin (IL)-11, which activates signaling molecules such [...]
Promise for a universal influenza vaccine: Scientists validate theory using 1918 flu virus
New research led by Oregon Health & Science University reveals a promising approach to developing a universal influenza vaccine—a so-called "one and done" vaccine that confers lifetime immunity against an evolving virus. The study, [...]
New Projects Aim To Pioneer the Future of Neuroscience
One study will investigate the alterations in brain activity at the cellular level caused by psilocybin, the psychoactive substance found in “magic mushrooms.” How do neurons respond to the effects of magic mushrooms? What [...]
Decoding the Decline: Scientific Insights Into Long COVID’s Retreat
Research indicates a significant reduction in long COVID risk, largely due to vaccination and the virus’s evolution. The study analyzes data from over 441,000 veterans, showing lower rates of long COVID among vaccinated individuals compared [...]
Silicon Transformed: A Breakthrough in Laser Nanofabrication
A new method enables precise nanofabrication inside silicon using spatial light modulation and laser pulses, creating advanced nanostructures for potential use in electronics and photonics. Silicon, the cornerstone of modern electronics, photovoltaics, and photonics, [...]
Caught in the actinium: New research could help design better cancer treatments
The element actinium was first discovered at the turn of the 20th century, but even now, nearly 125 years later, researchers still don't have a good grasp on the metal's chemistry. That's because actinium [...]
Innovative Light-Controlled Drugs Could Revolutionize Neuropathic Pain Treatment
A team of researchers from the Institute for Bioengineering of Catalonia (IBEC) has developed light-activated derivatives of the anti-epileptic drug carbamazepine to treat neuropathic pain. Light can be harnessed to target drugs to specific [...]
Green Gold: Turning E-Waste Into a Treasure Trove of Rare Earth Metals
Scientists are developing a process inspired by nature that efficiently recovers europium from old fluorescent lamps. The approach could lead to the long-awaited recycling of rare earth metals. A small molecule that naturally serves [...]
Cambridge Study: AI Chatbots Have an “Empathy Gap,” and It Could Be Dangerous
A new study suggests a framework for “Child Safe AI” in response to recent incidents showing that many children perceive chatbots as quasi-human and reliable. A study has indicated that AI chatbots often exhibit [...]
Nanoparticle-based delivery system could offer treatment for diabetics with rare insulin allergy
Up to 3% of people with diabetes have an allergic reaction to insulin. A team at Forschungszentrum Jülich has now studied a method that could be used to deliver the active substance into the [...]