Can vaccines end the pandemic?

 New coronavirus vaccines can prevent diseases, but no one knows whether they can stop the virus.

In early December 2020, Indonesia announced an unusual plan to vaccinate the people of the country with COVID-19. Indonesia plans to provide vaccines to normal healthy adults between the ages of 18 and 59, instead of providing vaccines to endangered groups such as health workers and the elderly.

The goal of the plan is to end the epidemic in Indonesia. Its target is not disadvantaged people, but people who spread the virus disproportionately-the center of the country's social network. "Our goal is herd immunity," said Amin Subandriyo, a biologist and director of the Akman Institute of Molecular Biology in Jakarta, Indonesia.

 

But there is a major problem with Indonesia's plan: no one knows whether the first successful new coronavirus vaccines can bring herd immunity. Tests have shown that vaccines can prevent people from getting sick, but they cannot prevent people from contracting and spreading viruses.

This distinction is often overlooked, but some researchers say it is crucial in determining the long-term development of this epidemic, not only in Indonesia, but throughout the world. Although there is often an unexplained assumption that vaccines will restore us to a state similar to normal life-this is a "break-through" ending of horror stories-it is not yet clear whether they have this power .

Not the holy grail

Although vaccines are considered one of the most valuable tools in medicine, their functions are much more complicated than people usually realize. In the best case, the vaccine can crush pathogens like a sledgehammer. For example, vaccines for smallpox and polio have completely eliminated the pathogen. A key to the success of these vaccines is that they provide sterile immunity-the vaccinated person will not be infected with the disease-causing virus and will not spread it. When a sufficiently large proportion of the population is immunized, herd immunity will be achieved: the pathogen cannot find enough new hosts to continue to multiply, and the epidemic will gradually disappear.

But smallpox and polio are not typical. More commonly, vaccines cannot perfectly protect recipients from infection and prevent the spread of pathogens. Take influenza as an example. The virus can invade the cells of some vaccine recipients, multiply in the cells without producing any symptoms, and then continue to infect other people, causing them to get sick or even die. The vaccinated individuals did not cut off the chain of transmission, but acted as a link in the chain of transmission, bringing pathogens to vulnerable hosts that were not vaccinated. This situation is common in respiratory diseases such as COVID-19, because pathogens can easily invade our respiratory tract and multiply there, then trigger a major immune response.

 

Experts say that if the vaccine does not stop the spread of the virus, we will not see the pandemic end suddenly, even if most people have the vaccine and agree to take it. As the speed of transmission slows, vaccination restrictions may gradually relax, and more people will be protected by vaccination because people have a better understanding and control of disease risks. Dobromir Dimitrov, a senior scientist at the Fred Hutchinson Cancer Research Center in Seattle, said: "We may not know how quickly it will return to normal. This may also vary from country to country, or even from region to region. In many ways, this will become a new normal.” Researchers believe that wearing masks and maintaining a certain degree of social distancing will take a long time.

Can't guarantee the restoration of the past life

Returning to the social activities that we often carried out before the outbreak of the new crown epidemic will be a tricky and remote process.

"To be honest, I think this is the most important issue that has the greatest impact on daily life." Fred Hatch's virologist Larry Corey said. Corey gave an example to illustrate the dilemma we will face in 2021: an office gathering to celebrate a colleague’s promotion. Most people have been vaccinated, but someone in the office lives with an elderly relative who has a serious illness. If we have a vaccine that prevents 50% of infections and a vaccine that prevents 90% of infections, the relative potential risks may be very different. "Can you hold this party without feeling guilty? How will you decide?" Corey asked. "These are the decisions we make every day. It affects people's behavior and social behavior."

Dimitrov and several other infectious disease researchers released a research report that uses a model to quantify the potential health effects of different types of vaccines. They found that with the introduction of vaccines, a vaccine that can prevent 90% of symptomatic diseases and most infections can relatively easily reduce 50% of cases and deaths in 2021. They found that a vaccine that can prevent 90% of diseases but not most infections requires twice the amount to provide the same health benefits.

 

So can the real new coronavirus vaccine protect against the virus itself? So far, all published trials have focused on how vaccines prevent symptomatic cases, but we also have some signs that they may also reduce asymptomatic cases. At the same time, researchers are continuing to study other vaccines, which may be cheaper, more effective against infections, or better than previous vaccines in other ways. Paul Griffin, an infectious disease expert at the University of Queensland, said: "We may never find a perfect vaccine. They all have their own advantages and disadvantages."

How the vaccine works

The COVID-19 pandemic may bring you into a world you didn't know much about before-the world of vaccine development. Maybe you want to know that vaccines usually take several years to produce. Or you may be wondering how the approximately 200 SARS-CoV-2 vaccines under development should work.

Basically, the vaccine needs to trick your immune system into thinking that an infection has occurred. In this way, you can build a tactical arsenal, once the pathogen appears in your body, you can eliminate it and release a non-functional virus into the body.

If researchers intervene appropriately, this modified virus can still stimulate your immune system without making you sick. One way to weaken the power of the virus is to cultivate it in another species, just as researchers use chicken embryo cells to make a measles vaccine. Developers can also expose the virus to chemicals such as heat or formaldehyde to get an inactivated vaccine. There are also vaccines that allow your own cells to produce key proteins that help fight the virus. These include DNA vaccines and RNA vaccines. DNA variants can push the SARS-CoV-2 spike protein gene into your cells. Once it is there, the DNA will be processed like your own genetic information. Your body makes RNA-temporary copies of genes-and builds viral proteins from this template. On the other hand, RNA vaccines eliminate several steps in the production process: These vaccines provide RNA templates from which cells assemble proteins.

For RNA vaccines or DNA vaccines to work successfully, the key is to allow genetic material to enter your cells, enter the protein production mechanism, and allow the viral proteins to proliferate properly. Sometimes, vaccine developers put the DNA or RNA of another virus into their genome and use it as a kind of transportation container. These are called viral vector vaccines. Don't worry, you won't get sick because of this-the researchers disabled the virus to prevent this from happening.

It is also possible to create a vaccine that does not force cells to make viral proteins, but delivers them directly. Some companies are studying this type of SARSCoV-2 vaccine, which is often called a protein vaccine. In general, vaccine developers spend a lot of time on design. The complexity of the immune system makes it difficult to develop vaccines. When it comes to SARSCoV-2, any of these vaccine types may stand out from the crowd and ultimately help contain COVID-19.