醫學評審人：Anju Goel，醫學博士，公共衛生碩士
更新時間：2021年3月1日
桑葛石（譯）
在COVID-19新冠狀病毒首次出現後不久，科學家們就開始研發疫苗，以防止感染的進一步傳播。這是一項艱鉅的任務，最初研究人員對病毒知之甚少，能否研發出疫苗也是未知之數。後來科研人員取得了前所未有的進展，設計了多種疫苗，而且比以往其它疫苗的研發速度快，取得了驚人的進步。全球範圍內不同的商業化和非商業化團隊團隊使用了一些或相似或不同的方法來解決疫苗研發問題。
普通疫苗研發過程疫苗的研發需要一系列的程式來確保最終產品的安全性有效性。首先，動物的基礎研究和臨床前研究的階段；第二，疫苗進入第一階段研究，重點是測試安全性；第三，進如第二階段研究，重點是測試有效性；第四，進行三期試驗，研究數萬名患者的有效性和安全性。如果在這一點上情況仍然良好，疫苗可以提交FDA審查。
在應對COVID-19時，最先是由CDC（疾病防治中心）在專門的緊急授權狀態下發布疫苗。也就是說疫苗還沒有做FDA（食品及藥物管理局）所要求的進一步試驗研究就分發給了一部分公眾，不過FDA和CDC也將繼續監測任何意外的安全問題。
我們關心的是，截止目前，哪些疫苗可用，誰能使用這些疫苗，以及安全性如何。
COVID-19疫苗目前，美國已經有三種疫苗獲批上市，獲批疫苗生廠商分別為輝瑞、Moderana和強生公司。
截至2020年12月初，全球已有50多種不同的疫苗進入人類臨床試驗。不過更多的的疫苗仍處於臨床前研究階段，即動物研究或其他實驗研究。在美國，另外三種COVID-19疫苗目前處於三期臨床試驗的某個階段。如果它們顯示出有效性和安全性，更多正在研發的疫苗可能最終獲批。
即使COVID-19疫苗經過FDA授權獲批的上市，並不意味著每個人都能馬上能注射，因為產能還不夠，在醫療保健部門工作的人和需要長期護理的居民可能會被優先注射。隨著產能的增加，更多的安全性和有效性的資訊能被掌握，也將有更多的人能夠注射這些疫苗。
疫苗一般如何發揮功效？所有疫苗的設計目標都有一定相似性，疫苗是為了幫助人們對COVID-19的病毒產生免疫力，以防止人們出現新冠病毒症狀。注射疫苗後，如果人們暴露在病毒中，其感染病毒的機會將大大降低。
免疫系統啟用免疫系統是包含一系列複雜細胞的系統，用於識別和消除體內的傳染性生物，如病毒。為了設計有效的疫苗，研究人員放大了人體免疫系統的潛在力量，用許多不同的複雜方式做到這一點。
為了消滅病毒，人體有著很多複雜的生理機制，其中，被稱為T細胞和B細胞的免疫細胞起著重要作用。T細胞識別病毒上的特定蛋白質並結合它們，最終殺死病毒；B細胞在製造抗體方面起著至關重要的作用，小蛋白也能中和病毒並幫助破壞病毒。如果身體遇到一種新的病毒，這些細胞需要一段時間才能學會識別它們，這就是人在第一次生病後需要一段時間才能康復的原因之一。
T細胞和B細胞在長期保護性免疫中也起著重要作用。再次感染後，某些長壽命的T細胞和B細胞會立即啟動識別病毒上的特定蛋白質，如果它們看到這些相同的病毒蛋白，它們會在人體有機會生病之前殺死病毒，可能人們還會生病，但不像第一次被感染時那麼嚴重。
疫苗啟用長期免疫疫苗可以幫助人體發展長期保護性免疫，而不必首先經歷主動感染。疫苗使人體的免疫系統暴露在某種抗原下，幫助免疫系統製造對抗這些抗原的T細胞和B細胞，這種抗原可能是某種病毒，例如：COVID-19病毒。由於人體在疫苗下激活了這些細胞，如果人體將來暴露在病毒中，這些細胞就會立即殺滅病毒。因此，人體不太可能有嚴重的感染症狀，或者可能根本沒有任何症狀。
COVID-19疫苗如何與免疫系統相互作用以獲得這種保護性免疫方面存在差異，正在研發的COVID-19疫苗可分為兩大類：
經典疫苗：包括活（弱）病毒疫苗、滅活病毒疫苗和基於蛋白質的亞基疫苗。
新型疫苗：包括基於核酸的疫苗(如基於mRNA的疫苗)和病毒載體疫苗。
經典的疫苗方法已經被用來製造市場上幾乎所有的人類疫苗。從2020年12月開始在美國進行三期試驗的五種COVID-19疫苗中，除一種用的經典方法以外，其它疫苗都是基於新方法。
活病毒疫苗是使用一種仍然活躍和存活的病毒來引起免疫反應。病毒已經被改變和嚴重削弱，以至於它幾乎沒有引起任何症狀，如麻疹、腮腺炎和風疹疫苗。由於它們仍然有活病毒，這些型別的疫苗需要更廣泛的安全測試，與其他方法相比，它們可能更容易引起重大不良事件。對於免疫系統受損的人來說，這種疫苗可能是不安全的，此外，活病毒疫苗需要小心儲存讓疫苗處於有效狀態。但活病毒疫苗的優點是會引起持續很長時間的強烈的免疫反應，通常一針就可以達到免疫的效果，這些疫苗也不需要使用額外的佐劑。
滅活疫苗是最早研製的普通疫苗之一，將滅活的病毒注入體內，它不能真正感染人體，但免疫系統仍然被啟用，並觸發長期免疫記憶，幫助保護人體，如果小兒麻痺症疫苗。使用滅活病毒的疫苗需要注射多劑。它們不會引起像活疫苗那樣強烈的免疫反應，也比活病毒疫苗更安全、更穩定。滅活病毒疫苗和弱病毒疫苗需要專門的安全協議和完善的產品研發和生產模式。
基於蛋白質的亞基疫苗該類疫苗也是傳統疫苗，雖然可能使用了一些新的製備方法。基於蛋白質的亞基疫苗不使用滅活或減弱的病毒，而是使用病原體的一部分來誘導免疫反應。科學家們仔細地選擇了病毒中最能使免疫系統運轉的一小部分。對於COVID-19，可能使用到其一個蛋白質到一組蛋白質用於誘導免疫反應。有時，從活病毒中純化，能找到一種特定的蛋白質，被認為是免疫系統的良好觸發因素。有時，科學家也會選擇合成一種與病毒蛋白質幾乎相同的蛋白質，即重組蛋白，如有些乙肝疫苗由這種特定型別的蛋白質亞基製成的，還有人類乳頭瘤病毒(HPV)的疫苗。 這些疫苗不能引起任何活性感染，它們只含有一種病毒蛋白或一組蛋白質，而不是病毒複製所需的完整病毒機制。蛋白質亞基疫苗的優點是它們比使用整個病毒的疫苗產生的副作用更少。例如，20世紀40年代第一批針對百日咳的疫苗使用的是滅活菌，後來的百日咳疫苗採用了蛋白質亞基的方法，消除了明顯的副作用。蛋白質亞基疫苗的另一個優點是，它們的存在時間比新型疫苗技術長。蛋白質亞基疫苗也要缺點：蛋白質亞基疫苗需要使用佐劑來促進免疫反應，這可能有其潛在的不良影響；與使用活病毒的疫苗相比，免疫力可能不夠持久；與使用新技術的疫苗相比，研發時間更長。
核酸疫苗新型疫苗技術是圍繞核酸構建的：DNA和mRNA。DNA是人體從父母那裡繼承的遺傳物質，而mRNA是細胞用來製造蛋白質的遺傳物質的一種複製。
核酸疫苗來自實驗室人工合成的一小部分病毒的mRNA或DNA，這些mRNA或DNA最終用於觸發免疫反應，這種遺傳物質包含所需特定病毒蛋白的編碼。疫苗透過使用特定的載體分子，遺傳物質進入人體的細胞，然後人體細胞使用這些遺傳資訊來產生抗體。DNA和mRNA疫苗可以製造非常穩定安全的疫苗，也能產生強烈和持久的免疫反應。與DNA疫苗相比，mRNA疫苗可能具有更大的安全性。用DNA疫苗理論上有可能部分DNA會插入到人的DNA中，雖然通常不會產生這個問題，但在某些情況下，突變的風險可能導致癌症或其他健康問題，基於mRNA的疫苗並不構成這種理論風險。
在過去的幾年裡，研究人員研究了許多不同的基於mRNA的疫苗，用於艾滋病毒、狂犬病、寨卡病毒和流感等傳染病。然而這些疫苗都沒有達到試驗終點，基於DNA的疫苗也是如此，儘管其中一些已被批准用於獸醫用途。
輝瑞和Moderna的COVID-19疫苗都是基於mRNA的疫苗，其他幾種基於DNA和mRNA的疫苗目前正在全世界進行臨床試驗。
病毒載體疫苗病毒載體疫苗與基於mRNA或DNA的這些疫苗有很多相似之處，它們只是用一種不同的方式將病毒遺傳物質進入人體的細胞。病毒載體疫苗使用的是另一種病毒的一部分，這種病毒經過基因改造後不具有傳染性，這種病毒特別擅長進入人體細胞。如在滅活病毒（如腺病毒）的幫助下，編碼COVID-19尖峰蛋白的特定遺傳物質被帶入細胞，就像其他型別的mRNA和DNA疫苗一樣，細胞本身產生的蛋白質會觸發免疫反應。從技術的角度來看，這些疫苗可以被分離成病毒載體，可以繼續在體內複製和不能複製的病毒載體，但這兩種情況下的原則都是一樣的。
與基於mRNA的新方法相比，研究人員在病毒載體疫苗方面有更多的經驗。如這種方法已經被安全地用於埃博拉疫苗，並對其他病毒（如艾滋病毒）的疫苗進行了研究。其中一個優點是，與其他新的疫苗技術相比，生產單一疫苗免疫方法更容易，它也可能更容易適應世界各地許多不同設施的大規模生產。
阿斯利康強生製藥公司的COVID-19疫苗是基於一種非複製病毒載體。
此外，不同的疫苗具有不同的特性，以滿足不同的需要。有些需要一定的儲存條件，如冷凍；有些需要不具備的高科技設施中生產；有些疫苗可能提供更持久的免疫力；對某些人群，如老年人和免疫系統有問題的人，活病毒疫苗可能不會被建議使用。
然而，我們現在沒有足夠的資料來正確地比較這些疫苗的有效性，隨著時間的推移，資訊將變得更加清晰。一旦有多個疫苗可用，將是儘可能多的人接種疫苗的關鍵。只有透過這些努力，才能真正結束這一流行病。
【原文】文末附原文連結
Types of COVID-19 Vaccines How They Work: Differences and Similarities
By Ruth Jessen Hickman, MD
Medically reviewed by Anju Goel, MD, MPH
Updated on March 1, 2021
Very soon after the first appearance of the new coronavirus (SARS-CoV-2) that causes COVID-19, scientists began working to develop vaccines to prevent the spread of infection and end the pandemic. This was a huge task, because little was known about the virus initially, and at first it wasn’t even clear if a vaccine would be possible.
Since that time, researchers have made unprecedented strides, designing multiple vaccines that may ultimately be utilized on a much faster timeframe than has ever been done for any previous vaccine. Many different commercial and non-commercial teams over the world have used some overlapping and some distinct methods to approach the problem.
General Vaccine Development ProcessVaccine development proceeds in a careful series of steps, to make sure the final product is both safe and effective. First comes the phase of basic research and preclinical studies in animals. After that, vaccines enter small phase 1 studies, with a focus on safety, and then larger phase 2 studies, with a focus on effectiveness.
Then come much larger phase 3 trials, which study tens of thousands of patients for both effectiveness and safety. If things still look good at that point, a vaccine can be submitted to the FDA for review and potential release.
In the case of COVID-19, the CDC is first releasing qualifying vaccines under a specialized Emergency Use Authorization status. That means they will be available to some members of the public even though they haven’t received as extensive study as is required for a standard FDA approval.
Even after the release of vaccines under Emergency Use Authorization, the FDA and CDC will continue to monitor for any unexpected safety concerns.
COVID-19 Vaccines: Stay up to date on which vaccines are available, who can get them, and how safe they are.
COVID-19 Vaccine UpdateA COVID-19 vaccine developed by Pfizer was granted an Emergency Use Authorization on December 11, 2020, based on data from its phase 3 trials. As of mid-December 2020, it is the only vaccine to achieve this.
A vaccine sponsored by Moderna has also submitted to the FDA for Emergency Use Authorization, based on data of effectiveness and safety in their phase 3 trial. AstraZeneca has also submitted preliminary information on their COVID-19 vaccine to the FDA based on data from phase 3 trials.
As of early December 2020, more than 50 different vaccines worldwide have moved into clinical trials in human beings. Even more vaccines are still in the preclinical phase of development (in animal studies and other laboratory research).
In the U.S., three additional COVID-19 vaccines are currently in some stage of phase 3 trials or will enter very soon. Several other phase 3 trials are ongoing worldwide. If they demonstrate effectiveness and safety, more of the vaccines under development may ultimately be released.
Even though a COVID-19 vaccine has been released by the FDA, not everyone will be able to get it right away, because there won’t be enough. Priority will go to certain people, like people who work in healthcare and residents of long-term care facilities.
As more vaccines become available and even more information about safety and efficacy become known, more people will be able to get these vaccines.
How Do Vaccines Work Generally?All the vaccines designed to target the new coronavirus disease share some similarities. All are made to help people develop immunity to the virus that causes the symptoms of COVID-19. That way, if a person is exposed to the virus in the future, they will have a greatly reduced chance of getting sick.
Immune System ActivationTo design effective vaccines, researchers leverage the natural powers of the body’s immune system. The immune system is a complex array of cells and systems that work to identify and eliminate infectious organisms (such as viruses) in the body.
It does this in a lot of different complex ways, but specific immune cells called T cells and B cells play an important role. T cells identify specific proteins on the virus, bind them, and ultimately kill the virus. B cells perform critical roles in making antibodies, small proteins that also neutralize the virus and help make sure it is destroyed.
If the body is encountering a new type of infection, it takes a while for these cells to learn to identify their target. That’s one reason it takes you a while to get better after you first become sick.
T cells and B cells also both play an important role in long-term protective immunity. After an infection, certain long-lived T cells and B cells become primed to recognize specific proteins on the virus right away.
This time, if they see these same viral proteins, they get right to work. They kill the virus and shut down the reinfection before you ever have a chance to get sick. Or, in some cases, you might get a little bit sick, but not nearly as ill as you did the first time you were infected.
Activation of Long-term Immunity by VaccinesVaccines, such as those designed to prevent COVID-19, help your body develop long-term protective immunity without having to go through an active infection first. The vaccine exposes your immune system to something that helps it develop these special T cells and B cells that can recognize and target the virus—in this case the virus that causes COVID-19.
That way, if you are exposed to the virus in the future, these cells will target the virus right away. Because of this, you’d be much less likely to have severe symptoms of COVID-19, and you might not get any symptoms at all. These COVID-19 vaccines differ in how they interact with the immune system to get this protective immunity going.
The vaccines under development for COVID-19 can be broken up into two overarching categories:
Classical vaccines: These include live (weakened) virus vaccines, inactivated virus vaccines, and protein-based subunit vaccines.
Next-generation vaccine platforms: These include nucleic acid-based vaccines (such as those based on mRNA) and viral vector vaccines.
Classic vaccine methods have been used to make almost all the vaccines for human beings currently on the market. Of the five COVID-19 vaccines that have begun phase 3 trials in the U.S. as of December 2020 (or which will start very soon), all but one are based on these newer methods.
Live (Weakened) Virus Vaccines
These vaccines are a classic type.
How They Are MadeA live virus vaccine uses a virus that is still active and alive to provoke an immune response. However, the virus has been altered and severely weakened so that it causes few, if any symptoms. An example of a live, weakened virus vaccine that many people are familiar with is the measles, mumps, and rubella vaccine (MMR), given in childhood.
Advantages and DisadvantagesBecause they still have live virus, these types of vaccines require more extensive safety testing, and they may be more likely to cause significant adverse events compared to those made by other methods.
Such vaccines may not be safe for people who are people who have impaired immune systems, either from taking certain medications or because they have certain medical conditions. They also need careful storage to stay viable.
However, one advantage of live virus vaccines is that they tend to provoke a very strong immune response that lasts a long time. It’s easier to design a one-shot vaccine using a live virus vaccine than with some other vaccine types.
These vaccines are also less likely to require the use of an additional adjuvant—an agent that improves the immune response (but which may also have its own risk of side effects).
Inactivated Virus Vaccines
These are also classic vaccines.
How They Are MadeInactivated vaccines were one of the first kinds of general vaccines to be created.They are made by killing the virus (or other type of pathogen, like a bacteria). Then, the dead, inactivated virus is injected into the body.
Because the virus is dead, it can’t really infect you, even if you are someone that has an underlying problem with your immune system. But the immune system still gets activated and triggers the long-term immunological memory that helps protect you if you’re ever exposed in the future. An example of an inactivated vaccine in the U.S. is the one used against polio virus.
Advantages and DisadvantagesVaccines using inactivated viruses usually require multiple doses. They may also not provoke quite as strong a response as a live vaccine, and they may require repeat booster doses over time. They are also safer and more stable to work with than with live viruses vaccines.
However, working with both inactivated virus vaccines and weakened virus vaccines requires specialized safety protocols. But they both have well-established pathways for product development and manufacturing.
COVID-19 Vaccines in DevelopmentNo vaccines undergoing clinical trials in the U.S. are using either live virus or inactivated virus approaches. However, there are several phase 3 trials taking place abroad (in China and India) that are developing inactivated virus vaccine approaches, and at least one vaccine is being developed utilizing a live vaccine method.6
Protein-Based Subunit VaccinesThese are also a classical type of vaccine, although there have been some newer innovations within this category.
How They Are MadeInstead of using inactivated or weakened virus, these vaccines use a part of a pathogen to induce an immune response.
Scientists carefully select a small part of the virus that will best get the immune system going. For COVID-19, this means a protein or a group of proteins. There are many different types of subunit vaccines, but all of them use this same principle.
Sometimes a specific protein, one that is thought to be a good trigger for the immune system, is purified from live virus. Other times, scientists synthesize the protein themselves (to one that is almost identical to a viral protein).
This lab synthesized protein is called a “recombinant” protein. For example, the hepatitis B vaccine is made from this type of specific type of protein subunit vaccine.
You might also hear about other specific types of protein subunit vaccines such as ones based on virus-like particles (VLPs). These include multiple structural proteins from the virus, but none of the virus’ genetic material. An example of this type of vaccine is the one used to prevent human papillomavirus (HPV).
For COVID-19, almost all the vaccines are targeting a specific viral protein called the spike protein, one which seems to trigger a strong immune response. When the immune system encounters the spike protein, it responds like it would as if it were seeing the virus itself.
These vaccines can’t cause any active infection, because they only contain a viral protein or group of proteins, not the full viral machinery needed for a virus to replicate.
The different versions of the flu vaccine provide a good example of the different types of classical vaccines available. Versions of it are available made from live virus and from inactivated virus. Also, protein subunit versions of the vaccine are available, both ones made from purified protein and ones made from recombinant protein.
All these flu vaccines have slightly different properties in terms of their effectiveness, safety, route of administration, and their requirements for manufacturing.
Advantages and DisadvantagesOne of the advantages of protein subunit vaccines is that they tend to cause fewer side effects than those that use whole virus (as in weakened or inactivated virus vaccines).
For example, the first vaccines made against pertussis in the 1940s used inactivated bacteria. Later pertussis vaccines used a sub-unit approach and were much less likely to cause significant side effects.
Another advantage of the protein subunit vaccines is that they have been around longer than newer vaccine technologies. This means that their safety is better established overall.
However, protein subunit vaccines require the use of adjuvant to boost the immune response, which can have its own potential adverse effects. And their immunity may not be as long-lasting compared to vaccines that use the whole virus. Also, they may take longer to develop than vaccines using newer technologies.
Vaccines in Development for COVID-19The Norovax COVID-19 vaccine is a type of subunit vaccine (made from a recombinant protein) expected to begin phase 3 clinical trials in the U.S. in December 2020.15 Others may enter phase 3 trials in 2021.
Nucleic-Acid Based VaccinesThe newer vaccine technologies are built around nucleic acids: DNA and mRNA. DNA is the genetic material you inherit from your parents, and mRNA is a kind of copy of that genetic material that is used by your cell to make proteins.
How They Are MadeThese vaccines utilize a small section of mRNA or DNA synthesized in a lab to ultimately trigger an immune response. This genetic material contains the code for the specific viral protein needed (in this case, the COVID-19 spike protein).
The genetic material goes inside the body’s own cells (by using specific carrier molecules that are also a part of the vaccine). Then the person’s cells use this genetic information to produce the actual protein.
This approach sounds a lot scarier than it is. Your own cells will be used to produce a type of protein normally made by the virus. But a virus needs a lot more than that to work. There’s no possibility of being infected and getting sick.
Some of your cells will just make a little COVID-19 spike protein (in addition to the many other proteins your body needs daily). That will activate your immune system to start forming a protective immune response.
Advantages and DisadvantagesDNA and mRNA vaccines can make very stable vaccines that are very safe for manufacturers to handle. They also have the good potential to make very safe vaccines that also give a strong and long-lasting immune response.
Compared to DNA vaccines, mRNA vaccines may have an even greater safety profile. With DNA vaccines, there is the theoretical possibility that part of the DNA might insert itself into the person’s own DNA. This usually wouldn’t be a problem, but in some cases there is a theoretical risk of a mutation that might lead to cancer or other health issues. However, mRNA-based vaccines don’t pose that theoretical risk.
In terms of manufacturing, because these are newer technologies, some parts of the world may not have the capacity to produce these vaccines. However, in places where they are available, these technologies have the capacity for much more rapid vaccine production than earlier methods.
It’s partly due to the availability of these techniques that scientists have been hopeful about producing a successful COVID-19 vaccine so much more quickly than has been done in the past.
Vaccines in Development for COVID-19Researchers have been interested in DNA and mRNA-based vaccines for many years. Over the past several years, researchers have worked on many different mRNA-based vaccines for infectious diseases like HIV, rabies, Zika, and influenza.
However, none of these other vaccines have reached the stage of development leading to official approval by the FDA for use in humans. The same is true of DNA-based vaccines, although some of these have been approved for veterinary uses.
Both the Pfizer and Moderna COVID-19 vaccines are mRNA-based vaccines. Several other DNA and mRNA-based vaccines are currently undergoing clinical trials around the world.
Viral Vector VaccinesViral vector vaccines have a lot of similarity to these vaccines based on mRNA or DNA. They just use a different mode of getting the viral genetic material into a person's cells.
Viral vector vaccines use part of a different virus, one that has been genetically modified to not be infectious. Viruses are particularly good at getting into cells.
With the help of an inactivated virus (such as an adenovirus) the specific genetic material encoding the COVID-19 spike protein is brought into the cells. Just as for other types of mRNA and DNA vaccines, the cell itself produces the protein that will trigger the immune response.
From a technical standpoint, these vaccines can be separated into viral vectors that can continue to make copies of themselves in the body (replicating viral vectors) and those that can't (non-replicating viral vectors). But the principle is the same in either case.
Just like other types of nucleic acid-based vaccines, you can’t get COVID-19 itself from getting such a vaccine. The genetic code only contains information to make a single COVID-19 protein, one to prompt your immune system but which won’t make you sick.
Advantages and DisadvantagesResearchers have a little more experience with viral vector vaccines compared to new approaches such as those based on mRNA. For example, this method has been safely used for a vaccine for Ebola, and it’s undergone study for vaccines for other viruses such as HIV.However, it’s currently not licensed for any applications for humans in the U.S.
One advantage of this method is that it may be easier to produce a single shot method for immunization in contrast to other new vaccine technologies. Compared to other newer vaccine techniques, it also may be easier to adapt for mass production at many different facilities around the world.
Vaccines in Development for COVID-19The AstraZeneca vaccine is based on a non-replicating viral vector. Janssen pharmaceutical company has also developed a COVID-19 vaccine based on a non-replicating viral vector that is currently in phase 3 trials. (It is the only one currently undergoing phase 3 trials in the U.S. that is a one-shot method).
Do We Need Different COVID-19 Vaccines?Ultimately, it’s hoped that multiple safe, effective vaccines will become available. Part of the reason for this is that it will be impossible for any single manufacturer to quickly release enough vaccine to serve the population of the whole world. It will be much easier to perform widespread vaccination if several different safe and effective vaccines are produced.
Also, not all these vaccines will have exactly the same properties. Hopefully, multiple successful vaccines will be produced that might help meet different needs.
Some require certain storage conditions, like deep freezing. Some need to be produced in very high-tech facilities that aren’t available in all parts of the world, but others use older techniques that can be more easily reproduced. And some will be more expensive than others.
Some vaccines may turn out to provide longer-lasting immunity compared to some others, but that isn’t clear at this time. Some might turn out to be better for certain populations of people, like the elderly or people with certain medical conditions. For example, live virus vaccines will probably not be advised for anyone who has problems with their immune system.
However, we don’t have enough data, now, to properly compare these vaccines in terms of their effectiveness (and hopefully minimal safety issues). That will become clearer with time.
Once one or more vaccines are available, it will be key for as many people as possible to get vaccinated. Only through such efforts will we really be able to end the pandemic.