Three COVID-19 vaccines build immunity

April 7, 2021


Pfizer-BioNTech COVID-19 vaccine (2020) E / U.S. Secretary of Defense / Wikimedia Commons / CC BY 2.0

Governments are distributing COVID-19 vaccines worldwide, helping more people build immunity to the virus.

A year into the unprecedented coronavirus pandemic, the Food and Drug Administration (FDA) has issued an Emergency Use Authorization (EUA) for COVID-19 vaccines from three companies: Pfizer-BioNTech, Moderna, and Johnson and Johnson. 

COVID-19 vaccine development was the fastest seen in history due to the world’s growing technological advances. The scramble for a vaccine was one of the first responses to the coronavirus because vaccines can increase immunity. Only the immune system can fight a virus off once an individual is infected. 

“Vaccines are the best way of going about preventing viruses. You can vaccinate large numbers of people and then look to generate herd immunity, where there’s just so many people who are immune to the disease that outbreaks really can’t be sustained,” said Diana Brainard, an infectious disease physician. 

COVID-19 spreads through air and droplets; social distancing, wearing a mask, and washing one’s hands can prevent the virus from spreading. Vaccinations take these precautions to another level. 

The Immune System by Grace Wu

“Vaccines are a game-changer when it comes down to being able to decrease the effect [of the virus] on people,” said Jason Lau, a pediatric resident at the University of California, Davis. “Once enough people have vaccinations, and there’s herd immunity, we can go about more towards our normal lives, which we really can’t quite do with just masking and social distancing.”

The immune system protects the human body from infection. Different types of white blood cells help fight the infection: macrophages eat up germs and dead cells but leave behind parts of the virus, or antigens, which are dangerous to the body; B-lymphocytes then come and produce antibodies that attack the antigens; lastly, the T-lymphocytes attack the infected cells. 

If an individual faces the same virus again, the T-lymphocytes left from the previous encounter, called memory cells, will know what to do and act quickly. After identifying the germ, B-lymphocytes will begin producing antibodies to fight it. 

The COVID-19 vaccines teach the T-lymphocytes and B-lymphocytes how to fight the virus without having an individual get the infection. 

“How we get immunity is to expose parts of the protein of the virus to our bodies, whether it be a messenger RNA (mRNA) method or an adenovirus that carries the spike protein,” Lau said. “It introduces the components of the virus to our body and allows us to mount an immune system response.”

The spike protein is a major antigen for the SARS-CoV-2 virus and appears on the virus particle’s surface, making it a target as the vaccine instruction to produce the protein. 

“The Pfizer, Moderna, and Johnson and Johnson vaccines express the spike in a stabilized prefusion conformation, and this is the conformation that will induce the immune response that can potently block virus infection,” said Jing Jin, a researcher and virologist. 

The three vaccines all express the same antigen but differ in how they deliver it.

A Medical Breakthrough

Pfizer-BioNTech’s COVID-19 vaccine was the first to be approved by the FDA, closely followed by Moderna’s vaccine a few days later. Both of these are the first few authorized mRNA vaccines, a significant accomplishment in the medical world. 

According to the National Human Genome Research Institute, mRNA is a single-stranded RNA molecule that complements a gene’s DNA strands. It is responsible for leaving the cell nucleus with the DNA’s genetic information as a template to help other structures produce proteins. 

While traditional vaccines prompt an immune response by putting a modified germ into the body, mRNA vaccines use a spike protein sequence to teach cells how to make a protein to stimulate an immune response and produce antibodies. 

“The mRNA will carry the genetic information of the SARS-CoV-2 virus. When it is injected into the human body, the mRNA will be used as a template to translate into a protein,” said Chunling Wang, a virologist. “That will trigger the immune response, and the body will produce antibodies and other major effectors to protect us from future infection.”

Both mRNA vaccines require two shots, spaced 21 days apart for Pfizer and 28 days apart for Moderna. 

“The big efficacy studies were done for Moderna and Pfizer with the idea of giving an initial vaccine called a prime, which gives your body the stimulation to make the antibodies, and then a boost, which is like a reminder,” Brainard said.

Jin expressed similar reasoning. 

“From the clinical trial data provided by Moderna and Pfizer, the first shot couldn’t provide high enough protection, and that’s quite normal,” Jin said. “Memory cells will just stay in your body but not produce the antibody until your body faces a second round of the foreign antigen infection. Then, those memory cells will quickly respond and have a higher immune response compared to the first response. That’s called immune boosting.”

Due to the booster shot, Pfizer and Moderna both yield high efficacy rates — 95% efficacy for Pfizer and 94.1% efficacy for Moderna — for protecting an individual against the coronavirus after the second shot. 

Storing mRNA vaccines prove to be a challenge, however. Pfizer’s vaccine must be kept in an ultra-cold freezer between minus 80 and minus 60 degrees Celsius. In comparison, Moderna’s vaccine must be kept in a freezer between minus 25 and minus 15 degrees Celsius. Furthermore, the vaccines cannot be stored again to use the following day. 

“Once you thaw it, you have to use it within a limited time, so they are not that stable,” Jin said. “It’s pretty much impossible to deliver this kind of vaccine to the whole world, especially to a developing country.”

One Shot and Done

In contrast to the Pfizer and Moderna vaccines, Johnson and Johnson’s Janssen COVID-19 vaccine is a viral vector vaccine, which uses a modified adenovirus to store and carry instructions. Adenovirus 26 is another virus that can enter cells but would not replicate itself or cause illness. 

Because the vaccine uses another virus vector, the immune system will develop an immune response to both COVID-19 and the adenovirus, making a second dose unnecessary. 

“One of the benefits is that it only requires one dose. But because it is only one dose, it’s not as protective as the [Pfizer and Moderna vaccines],” Wang said. “The second dose won’t do anything because you already have the immune response from your first dose for another virus vector as well.”

Therefore, the vaccine trials did not include a second shot. 

“When you inject the second shot, the immune response elicited by the first shot will limit the effectiveness of your second shot,” Jin said. “It’s also based on their data; one shot has already provided enough protection, and that’s how the clinical trial was set up.”

Reports show that Johnson and Johnson’s vaccine has a 75% efficacy rate. It also takes extra time to develop and grow the modified virus used in the vaccine compared to using mRNA. 

On the other hand, since the adenovirus contains double-stranded DNA and has a protective coat surrounding the genetic material, the Johnson and Johnson vaccine is less fragile than the mRNA vaccine, making storage much easier. The vaccine must be kept in a refrigerator between 2 and 8 degrees Celsius; this simpler storage method allows it to be accessible to more people worldwide.

An Uncertain Future

Despite the vaccine developments, the pandemic is far from over, with coronavirus variants appearing in various countries. 

“The variants are to be expected because that’s what viruses do,” Brainard said. “Viruses survive by changing themselves, and they change themselves so that they can avoid the body’s immune system.”

To combat those mutations, companies are looking at various strategies. Especially with mRNA, it is easier to modify the vaccine to carry the new virus sequence, which would signal the immune system to produce a different antibody. 

“There’s active research into how effective the current vaccines are against the variants and whether or not a booster shot designed to target those variants and provide a broader protection would be necessary,” Brainard said.

The ongoing research will be crucial in determining future steps. 

“Because the COVID-19 infection outcome is much much worse, the worst-case scenario is if the SARS-CoV-2 continues and we need to get a vaccine every year,” Wang said. “Both Pfizer and Moderna are working on follow-up booster doses for vaccines against virus mutations. If the virus keeps on circulating, if we don’t have herd immunity, if people don’t get the vaccine, there might be even more mutations.”

Even so, herd immunity in one country will not help.

It’s a competition between human beings’ immunity and virus evolution.”

— Jing Jin

“Now it’s just a competition between human beings’ immunity and virus evolution. If you look at the data nationally, the cases are rising, and this is under the condition with parts of the population already fully vaccinated,” Jin said. “If other countries cannot control the variants, eventually the U.S. will also have new problems. With the new variants circulating, it’s very hard to predict what will happen, but it will not end very soon.”

However, the world is, undoubtedly, a step closer to returning to normal as companies and the government are doing their best to make the vaccines more available. 

Carly Ramirez, a senior who works in food service, has recently gotten her first Pfizer vaccine. She is hopeful that the vaccine will be vital in ending the pandemic by creating immunity. 

“I’ve always had trust in the vaccines. I know a lot of people are worried about how fast the vaccines were developed or if they got the right amount of testing or if side effects are fatal,” Ramirez said. “A lot of people say they want to wait for a better one, but I totally disagree with that. I’d rather risk getting the vaccine than getting the coronavirus itself.”

There is no telling how long the pandemic will last, but people can do their part to stay safe by taking any protection measures available. 

“Vaccines are the most powerful weapon humans have against infectious diseases. Unfortunately, nobody will 100% guarantee that you will be protected, even if you get the two doses for Pfizer or Moderna because the immune response is different for each individual,” Wang said. “Whether you have the vaccine or not, we are still recommended to take universal precautions to protect yourself and protect others.”

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