Editor's comments:
Since the AstraZeneca (British) and Sinovac (Chinese) COVID-19 Vaccines have both been utilized in Bali of recent months I tought it was important for those of you in Bali to know the difference and the latest research on both vaccines.
Zahim Mohd/NurPhoto/Getty Images
The number of vaccines being used to fight the COVID-19 pandemic continues to grow, with several international candidates that could soon enter the U.S. market.
The University of Oxford and AstraZeneca have teamed up in the United Kingdom to produce a recombinant vaccine made from a modified chimpanzee adenovirus. Another candidate is from China’s Sinovac Biotech. The Sinovac vaccine uses more traditional vaccine technology, relying on inactivated virus particles to produce an immune response.
Neither of these vaccines has been approved for regular or emergency use in the United States yet. Numerous trials are underway and applications could be presented to the Food & Drug Administration (FDA) in the future to add to the nation’s arsenal against COVID-19. Both vaccines are also being reviewed by the World Health Organization.
AstraZenecaSinovac
Official name AZD1222 CoronaVac
Effectiveness 76% 56%–65%Trusted Source
Dosage 2 doses, 28 days apart 2 doses, 21 days apart
Storage standard refrigeration standard refrigeration
Type chimpanzee adenovirus inactivated virus
Approval status U.S. and international clinical trials Various international clinical trials
U.S. availability 300 million doses owned, but not approved for use none
AstraZeneca vs. Sinovac effectiveness
Both the AstraZeneca and Sinovac vaccines are still undergoing clinical trials across the globe, so there is some uncertainty as to how effective each vaccine is against COVID-19.
There was some controversy over the effectiveness of AstraZeneca’s vaccine in late 2020 when it was revealed that some people in the early study groups only received half doses of the vaccine.
While AstraZeneca claimed that the vaccine was 70-percent effective, it was later disclosed that the effectiveness was 62 percentTrusted Source in people who received two full doses, and closer to 90 percent in people who received one half and one full dose. AstraZeneca used these two percentages to average an effectiveness rate of 76 percent.
Data on Sinovac’s CoronaVac vaccine is limited since a number of international studies on the vaccine are still underway. In one report, investigators report that 97 to 100 percent of people who received the vaccine in clinical trials developed antibodies to COVID-19, but not all of the immune response markers measured in other studies were investigated for the CoronaVac vaccine.
Another report on the effectiveness of CoronaVac reveals that phase 3 clinical trial results have yet to be released by Sinovac, but a trial in Chile shows an effectiveness rate of just 56.5 percentTrusted Source after full vaccination with CoronaVac.
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AstraZeneca vs. Sinovac side effects
Side effects for many of the vaccines currently available for COVID-19 are similar, with injection site pain and soreness leading the most common reactions.
For the CoronaVac vaccine, injection site pain and soreness was the most common side effect, reported by 17 to 21 percent of people who received various doses of the vaccines.
In most cases, the reactions were mild and resolved within 2 days. There was one case in the phase 1 trial for the vaccine where a recipient developed an allergic skin reaction with welts but was treated with antihistamines and steroids and resolved in 3 days.
Systemic reactions that affected more than just the injection site included:
fatigue
diarrhea
muscle weakness
These symptoms were reported far less than injection site pain, according to trial data.
Rashes on People of Color
Redness, irritation, and hives are easily given away by redness and raised areas on white skin, but detecting hives or rashes on other skin tones may be more difficult.
If you have black or brown skin, it can be a challenge to see redness, but you can still detect hives and skin irritation through:
itching
swelling
inflammation
raised bumps
If you experience swelling in your mouth or throat or have trouble breathing, this is a sign of an anaphylactic allergic reaction. You should call 911 or go to the nearest emergency room immediately.
The AstraZeneca vaccine attracted a lot more attention for its side effects after some people developed blood clots after vaccination.
Administration of the vaccine was paused in many parts of the world as regulators investigated the clots, concluding they were a very rare side effect — impacting about 86 people out of the 25 million who had received the vaccine. European regulators allowed AstraZeneca to resume its vaccination program, but some countries restricted its use to older adults.
Other side effects of the AstraZeneca vaccine, which were also rare, included cases of:
inflammation around the spinal cord
hemolytic anemia
high fevers
All of these symptoms resolved without additional problems. More common side effects included:
injection site pain
mild tenderness
fatigue
headache
muscle ache
chills
fever
Most of these reactions were mild, according to trial data, and resolved within a day or so after vaccination.
AstraZeneca vs. Sinovac vaccine types
Vaccination in general works by using small bits of information about a disease — like a protein spike or inactivated virus particle — to teach your immune system how to recognize and destroy the active virus.
Unlike the Pfizer and Moderna vaccines that use mRNA technology (pieces of COVID’s genetic code) to create immunity, the AstraZeneca and Sinovac vaccines use a more traditional route. This means that actual virus particles or genetic materials are combined with other materials to introduce small, harmless pieces of the virus into your body. Your immune system is able to use this information to design a defense, making it better equipped to fight the live virus.
Similar to the Johnson & Johnson COVID-19 vaccine, the AstraZeneca vaccine relies on a chimpanzee adenovirus to carry spike proteins from the coronavirus into your body to create an immune response.
The Sinovac CoronaVac vaccine also uses a virus to create immunity. However, instead of adenovirus, the vaccine uses inactivated particles of the SARS-CoV-2 virus that causes COVID-19.
What is a chimpanzee adenovirus?
Adenovirus is a very common virus. Usually causing mild illnesses like the common cold, adenoviruses are widespread and efficient. There are more than 50 types of adenoviruses that cause respiratory infections, and they are good at moving into and attacking the body in various ways. A chimpanzee adenovirus is an adenovirus that causes these infections in chimpanzees.
When modified for use in vaccines, these viruses are very efficient at helping to produce immune responses. These types of vaccines, like the AstraZeneca vaccine, are known as viral vector vaccines.
What does inactivated mean?
When a vaccine is made from an inactivated virus, this means that the part of the virus that causes disease is destroyed, but its basic genetic information remains.
When injected as a vaccine, the inactivated virus will train your immune system to fight the disease it causes, but won’t make you sick. Influenza, polio, and rabies vaccines use inactivated viruses to create immunity, but don’t create immune responses as strong as other types of vaccines.
Takeaway
Researchers are throwing everything they’ve got at the COVID-19 pandemic, and there are a number of different companies making many variations of a vaccine to fight the virus.
While there are only three vaccines currently approved for use in the United States, vaccine developers around the world are working on solutions, too. China’s Sinovac CoronaVac and the United Kingdom’s Oxford-AstraZeneca vaccines are two examples of these international options being studied across the globe.
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Last medically reviewed on May 14, 2021
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AstraZeneca. (2021). AZD1222 US phase III primary analysis confirms safety and efficacy.
astrazeneca.com/media-centre/press-releases/2021/azd1222-us-phase-iii-primary-analysis-confirms-safety-and-efficacy.html
COVID-19 vaccines safety tracking (CoVaST). (2021).
clinicaltrials.gov/ct2/show/NCT04834869?term=sinovac&cond=COVID-19&draw=3&rank=16
Dyer O. (2021). COVID-19: Chinese vaccines may need to improve efficacy, admit official.
bmj.com/content/373/bmj.n969
European Medicines Agency. (2021). AstraZeneca’s COVID-19 vaccine: Benefits and risks in context.
ema.europa.eu/en/news/astrazenecas-covid-19-vaccine-benefits-risks-context
Folegatti P, et al. (2020). Safety and immunogenicity of the ChAdOx1 nCoV-19 vaccine against SARS-CoV-2: A preliminary report of a phase 1/2, single-blind, randomised controlled trial.
sciencedirect.com/science/article/pii/S0140673620316044
Knoll MD, et al. (2020). Oxford-AstraZeneca COVID-19 vaccine efficacy.
thelancet.com/journals/lancet/article/PIIS0140-6736(20)32623-4/fulltext?fbclid=IwAR2zWTx86uAi8IhL5Vy_CBMs7y1xQ33ODsVeym3FVtUKdJXBx5dSJH7g6K0
Michaud J, et al. (2021). Global COVID-19 vaccine equity: U.S. policy and options to date.
kff.org/global-health-policy/issue-brief/global-covid-19-vaccine-equity-u-s-policy-options-and-actions-to-date/
Vaccine types. (2021).
hhs.gov/immunization/basics/types/index.html
World Health Organization. (2021). Status of COVID-19 vaccines within WHO EUL/PG evaluation process.
extranet.who.int/pqweb/sites/default/files/documents/Status_COVID_VAX_20Jan2021_v2.pdf
Zhang Y, et al. (2021.) Safety, tolerability, and immunogenicity of an inactivated SARS-CoV-2 vaccine in healthy adults aged 18–59 years: a randomised, double-blind, placebo-controlled, phase 1/2 clinical trial.
sciencedirect.com/science/article/pii/S1473309920308434
Medically reviewed by Cameron White, M.D., MPH — Written by Rachael Zimlich, RN, BSN on May 14, 2021
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Why Do You Need Two Doses for Some COVID-19 Vaccines?
How they work
Why two doses
Dosing timeframe
Timeframe changes
Immunity after first dose
Immunity after second dose
Why a second dose?
Interchangeable?
Side effects
Summary
FG Trade / Getty Images
COVID-19 is the illness caused by the novel coronavirus, SARS-CoV-2. While many people with COVID-19 get mild symptoms, others can become seriously ill. Several vaccines have been developed to protect against COVID-19.
The Food and Drug Administration (FDA) has so far authorized three COVID-19 vaccines for emergency use. Two of these are the Pfizer-BioNTech and Moderna vaccines. Both of these vaccines require two doses.
The Johnson & Johnson vaccine has also been authorized for emergency use. However, this vaccine only requires one dose.
Why do some vaccines require two doses? How long do you need to wait between doses? Do you have any immunity after the first dose?
This article will help explain why you need two doses of the Pfizer-BioNTech and Moderna vaccines, and will provide answers to many other questions, too.
How do these vaccines work?
The Pfizer-BioNTech and Moderna vaccines both use mRNA technology. The cells in your body naturally use mRNA all the time to create many different types of proteins that you need to stay healthy.
The mRNA in the two-dose COVID-19 vaccines provide the cells of your body with instructions on how to make the spike protein that’s specific to the new coronavirus. This spike protein is found on the surface of the virus. It uses this spike protein to attach to and enter a host cell in your body.
When you get your COVID-19 vaccine, your immune system processes information on the spike protein and generates an immune response to it. This includes the production of antibodies.
Vaccines hinge on a very important aspect of your immune system, which is the fact that it has memory. After your vaccination, your immune system continues to store information on the spike protein.
If you’re exposed to the new coronavirus, your immune system will then use this stored information to respond and protect you from the virus. This can help prevent you from becoming sick with COVID-19.
The entire immunity process typically takes around 2 weeks after the second dose of vaccine. That’s why you can still contract the new coronavirus and become ill if you’re exposed to it shortly after getting your vaccine.
Why do the Pfizer-BioNTech and Moderna vaccines require two doses?
During early studies, researchers found that the Pfizer-BioNTech and Moderna vaccines provoke a relatively weakTrusted Source immune response when given as just one dose. However, there was a stronger immune response when a second dose was added.
Basically, the first dose of the vaccine starts the process of building up protection. The second dose works to greatly reinforce this protection.
Here’s an analogy to help explain this: You and a friend are trying to move a heavy table across a room. Between the two of you, you’re able to get it partway there. Then, another couple of friends jump in to help, and you’re all able to move it the rest of the way.
Vaccines that need more than one dose aren’t that uncommon. Some examples of other vaccines that are part of a multi-dose series include:
the measle-mumps-rubella (MMR) vaccine
vaccines against hepatitis A and hepatitis B
the shingles vaccine
Are there other COVID-19 vaccines that require two doses?
Several other types of COVID-19 vaccines, including ones still under development, also require two doses. Some examples include:
Oxford-AstraZeneca: two doses given 8 to 12 weeksTrusted Source apart
Novavax: two doses given 3 weeksTrusted Source apart
Sputnik V: two doses given 3 weeksTrusted Source apart
Coronavac: two doses given 1 monthTrusted Source apart
Do some COVID-19 vaccines only require one dose?
The COVID-19 vaccine that’s been developed by Johnson & Johnson only requires one dose.
After reviewing safety and effectiveness data from large-scale clinical trials, the FDA has granted this vaccine Emergency Use AuthorizationTrusted Source in the United States.
How long do you need to wait between vaccines?
For both the Pfizer-BioNTech and Moderna vaccine, there’s a waiting period between the first and second dose. The timeframe between the doses depends on which vaccine you received.
Timeframe between two-dose vaccines
Pfizer-BioNTech. You receive your second dose 3 weeks (21 days) after your first dose.
Moderna. You receive your second dose 4 weeks (28 days) after your first dose.
Why do you need this waiting period?
The first dose helps to prime your immune system. It introduces it to the spike protein and allows it to generate a small immune response prior to the second dose. Time is needed to allow this process to develop properly.
It’s also important not to get your second dose too early, as this may impact the effectiveness of the vaccine.
According to guidelines from the Centers for Disease Control and Prevention (CDC)Trusted Source, you can receive your second dose up to 4 days earlier than recommended.
What happens if you wait for a longer period of time to get your second vaccine?
The CDCTrusted Source recommends that you receive your second dose as close to the required interval as possible.
You may be wondering what happens if you can’t get your second dose within the specified timeframes. The CDC has guidanceTrusted Source for this as well. In these situations, the second dose can be given up to 6 weeks (42 days) after the first dose.
We currently don’t know if delaying the second dose longer than this time has an impact on immunity.
If possible, try to schedule your appointment for your second dose on the day you get your first dose. If you didn’t schedule your second dose at this time, contact the location where you received your first dose to make an appointment.
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What level of immunity do you have after the first vaccine?
Even though the Pfizer-BioNTech and Moderna vaccines require two doses, you do get some immunity after you receive the first dose. Let’s examine this in a little more detail below.
Pfizer-BioNTech
Researchers working on the clinical trials for the Pfizer-BioNTech vaccine observed a vaccine effectiveness of 52 percent between the time of the first and second doses, which is a 21-day period.
However, the Pfizer-BioNTech vaccine may be more effective after the first dose than was previously thought. This information comes from a separate analysis from scientists in the United Kingdom.
These scientists wanted to look at vaccine effectiveness 15 days or more after people had received the first dose of the Pfizer-BioNTech vaccine. They found that vaccine effectiveness was actually closer to 89 to 91 percent 15 days after the first dose.
Moderna
In a reportTrusted Source submitted to the FDA, researchers discussed vaccine effectiveness in clinical trial participants who’d only gotten one dose of the vaccine.
A vaccine effectiveness of 50.8 percent was found up to 14 days after the first dose. Vaccine effectiveness was 92.1 percent beyond the first 14 days.
What level of immunity do you have after the second vaccine?
Now let’s look at immunity after receiving the second dose of the Pfizer-BioNTech or Moderna vaccine.
Pfizer-BioNTech
Pfizer-BioNTech immunity
Researchers working on the Pfizer-BioNTech vaccine clinical trial looked at vaccine effectiveness 7 days after the second dose. At this point, vaccine effectiveness was observed to be 95 percent.
And what about longer-term immunity? A separate study, currently in preprint, looked into this. This study followed people for 63 days after they’d received their second dose.
The researchers observed a strong antibody response following the second dose. While the overall levels of antibodies began to decrease slowly as time passed, they still remained high at the 63-day mark.
Moderna
Moderna immunity
Investigators working on the Moderna clinical trial evaluated vaccine effectiveness 14 days after trial participants had gotten their second dose.
Vaccine effectiveness was 94.1 percent at this point.
Researchers also published a separate study of the immune response to the Moderna vaccine 90 days after the second dose. This study was rather small, involving 34 participants.
High levels of antibodies were made following the second dose. Similar to the Pfizer-BioNTech study discussed above, antibody levels started to slowly decrease over time. However, immunity persisted at high levels at the 90-day mark.
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Is the second dose necessary?
Because both vaccines appear to have high effectiveness 14 days or more after the first dose, you may be wondering whether the second dose of the vaccine is actually necessary.
It’s true that there have been discussions amongst public health officials and scientists about the possibility of delaying or eliminating the second dose of these vaccines.
The thought process behind this is that either delaying or eliminating the second dose would enable a greater number of people to get some level of protection. It would also aid in stretching vaccine supplies to more people.
However, there are some concerns about doing this. It’s possible that overall immunity or vaccine effectiveness could be impacted. Additionally, lower levels of immunity could drive the emergence of more virus variants that can escape our current vaccines.
Additional research into delaying or eliminating second doses is needed. Currently, the FDA strongly recommendsTrusted Source continuing to follow the dosing schedule that was both tested in clinical trials and authorized for emergency use.
Can you get Pfizer for one dose and Moderna for the other?
The CDCTrusted Source notes that although there’s no preference for one vaccine over another, the two vaccines aren’t interchangeable. Because of this, it’s important to receive your second dose from the same product as your first dose.
This is one of the reasons why COVID-19 vaccine record cards are provided after you receive your first dose. These cards provide valuable information about which vaccine you received and the date on which you received it.
Is there a difference in the side effects between the first and second dose?
The two-dose COVID-19 vaccines have similar side effects, such as:
injection site reactions, which can include pain, redness, or swelling
fatigue
fever
chills
headache
body aches and pains
nausea
swollen lymph nodes
Side effects that are felt throughout your body, such as fever, fatigue, and headache, are more common after getting the second dose of the vaccine. This is true for both the Pfizer-BioNTech and Moderna vaccines.
Remember that the first dose of the vaccine generates a weaker response than the second dose. Because of this, you’re more likely to feel side effects after the second dose.
These side effects are actually a sign that an immune response is taking place in your body. But, it’s also normal not to have any side effects at all. The vaccine will still be boosting your immune response, even without symptoms.
The bottom line
Some COVID-19 vaccines, such as those produced by Pfizer-BioNTech and Moderna, require two doses. Others, such as the Johnson & Johnson vaccine, only require one dose.
Some vaccines require two doses because the immune response to the first dose is rather weak. The second dose helps to better reinforce this immune response.
When you get your COVID-19 vaccine, be sure to hold onto your vaccine record card afterward. This helps to ensure that you know which vaccine you received and when you’ll need to schedule your second dose.
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