Saturday, September 23, 2023

How Long Between Vaccine Doses

Viral Vector Vaccine Interval

How Long Should You Wait In Between COVID Vaccine Doses? Dr. Mallika Marshall Answers Your Questions

In an exploratory analysis of a Phase 3 randomized controlled trial of the Oxford-AstraZeneca COVID-19 vaccine, investigators evaluated the impact of variable timing of the second dose of vaccine. In this analysis, vaccine efficacy against primary symptomatic COVID-19 was higher with longer dose intervals. Vaccine efficacy was 55.1% when the interval between the two doses was less than 6 weeks and 81.3% when the interval was more than 12 weeks .

Will More Than One Dose Of Covid

The Pfizer-BioNTech vaccine requires two shots 21 days apart. The Moderna vaccine requires two shots 28 days apart. You must receive both shots of the same type of vaccine: either two shots of Pfizer or two shots of Moderna. The Janssen vaccine only requires one shot.

Everyone 18 and older is also recommended to get a booster shot of COVID-19 vaccine. Learn more about booster shots and third shots for immunocompromised individuals here.

Do You Still Need To Take Precautions After Being Vaccinated

If youve received both doses of the vaccine, its important to still continue to take precautions, including:

  • Wearing a mask.Wear a mask that covers your nose and mouth when youre around people outside of your household.
  • Hand-washing.Hand-washing is particularly important after being out in public, after coughing and sneezing, and after using the bathroom.
  • Practicing physical distancing. Try to stay at least 6 feet away from people outside of your household.
  • Avoiding crowded areas. Places that are crowded or poorly ventilated can make it easier to contract and transmit the virus.

These precautions are important because we currently dont know whether people whove been vaccinated can still spread the virus to others, even if they themselves dont develop symptoms.

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What Are Covid Booster Side Effects

After getting vaccinated for COVID-19, you might experience some temporary symptoms similar to those you might notice when you get a flu shot, such as a sore, swollen arm where you got the shot. You might run a fever and experience body aches, headaches and tiredness for a day or two. Chills, swollen lymph nodes can also occur.

These symptoms do not mean you are sick. They signal that your immune system is responding to the shots and building up protection against the coronavirus.

Vaccinating People With Previous Sars

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It is very important for people with previous SARS-CoV-2 infection to be vaccinated to prevent becoming infected again. NACI recommends that a complete series with a COVID-19 vaccine may be offered to individuals who have previously had PCR-confirmed SARS-CoV-2 infection. The number of doses will be updated based on evolving evidence.

Table 1 provides a summary of recommendations of products and doses by age.

People with SARS-CoV-2 infection can be vaccinated once they are no longer infectious and no longer have acute symptoms of COVID-19. The optimal timing of vaccination after infection is not certain.

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Why The New Recommendation

The benefit of extending the recommended time between shots among certain groups could help reduce the exceedingly rare risk of vaccine-associated myocarditis, an inflammation of the heart, according to information from Dr. Sara Oliver, a pediatrics infectious diseases expert, presented at a recent CDC advisory committee meeting.

Reported rates of myocarditis following Pfizer and Moderna vaccinations, while rare, have been highest among adolescent and young adult males. Rates of post-vaccination myocarditis have been lower among those whose intervals between the first and second COVID-19 shots were at least eight weeks.

If post-vaccination myocarditis does occur, it typically happens within a week of the vaccination, according to the CDC. Most patients who get post-vaccine myocarditis who receive medical treatment respond well and felt better quickly, the CDC said.

Another benefit to extending the interval between the first and second doses is that it may also improve how well the vaccine works, according to Oliver.

The CDC has eased its guidance on when people should wear masks in public indoor settings, but still recommends them in L.A. County.

If I Qualify For A Third Dose Of An Mrna Covid

The third mRNA COVID-19 vaccine dose should be the same vaccine product as the initial 2-dose mRNA COVID-19 primary vaccine series . If the mRNA COVID-19 vaccine product given for the first two doses is not available, the other mRNA COVID-19 vaccine product may be administered. A person should not receive more than three mRNA COVID-19 vaccine doses.

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Children Aged 5 To 11 Years

COVID-19 vaccination is recommended for all children aged 5 to 11 years.

Only the paediatric formulation of Pfizer COVID-19 vaccine is registered for use in children aged 5 to 11 years. The paediatric formulation differs from the adolescent/adult formulation in its concentration and recommended dosing . Children aged 5 to 11 years should not receive the adolescent/adult formulation of the Pfizer vaccine.

AstraZeneca and Moderna vaccines are not registered for use in children aged 5 to 11 years.

Booster doses are not recommended for people aged < 18 years, and there are currently no registered COVID-19 vaccines for use as a booster in this age group. Severe COVID-19 in children is uncommon and the primary course of COVID-19 vaccines generates a strong immune response. The benefit from additional doses of vaccine is likely to be small and current evidence does not suggest that booster doses are needed.

Direct benefits of vaccinating young children

Children aged 5 to 11 years in the following groups are most likely to benefit from COVID-19 vaccination because of their increased risk of severe outcomes and/or exposure:

  • children with medical risk factors for severe illness
  • Aboriginal and Torres Strait Islander children
  • children living in crowded conditions or outbreak areas.

Most children with SARS-CoV-2 infection are asymptomatic or have a mild illness. Vaccinating children aged 5 to 11 is anticipated to prevent:

Indirect benefits of vaccinating young children

People Who Are Immunocompromised

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COVID-19 vaccine is recommended for people who are immunocompromised because of their increased risk of severe illness with COVID-19.2 This dose is intended to address the risk of lowered or non-response to the standard 2 dose schedule.

A third primary dose of COVID-19 vaccine is recommended for people aged 12 years with severe immunocompromise at 26 months after the second vaccine dose.

A third primary dose is not currently recommended for children aged 5 to 11 years who are severely immunocompromised. ATAGI is reviewing emerging evidence on vaccination for children aged 5 to 11 years. This advice will be updated when more information is available.

An mRNA COVID-19 vaccine is preferred for the third dose. This is because most studies of third doses of COVID-19 vaccine in immunocompromised people have used mRNA vaccines. The AstraZeneca COVID-19 vaccine can be used for the third dose for people who have received AstraZeneca for their first 2 doses, or if there are contraindications to mRNA COVID-19 vaccines.

In severely immunocompromised people who have recently been recommended to receive a third dose for a primary COVID-19 vaccine course, a booster dose is recommended at 4 months, in line with the general population.

There are many causes and varying degrees of immunocompromise. The risk of COVID-19 will vary according to:

  • the number and type of underlying conditions
  • medical management
  • other factors.

For more details, see the:

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People With A Past Sars

People with SARS-CoV-2 infection can be vaccinated as soon as they have recovered from their acute illness, or can defer vaccination for up to 6 months after onset of the SARS-CoV-2 infection. People who have received an anti-SARS-CoV-2 monoclonal antibody or convalescent plasma should defer future doses of COVID-19 vaccine for at least 90 days.

Past infection reduces the risk of reinfection for at least 6 months.42-43 A 2-dose primary schedule is recommended in previously infected people and is safe and well tolerated.42,44,45 A 3-dose primary schedule is recommended in previously infected people with severe immunocompromise.

People who have prolonged symptoms from COVID-19 beyond 6 months after the initial illness can be vaccinated. Laboratory testing to detect current or past infection with SARS-CoV-2 before vaccination is neither necessary nor recommended.

Pfizer COVID-19 vaccination in people with a past SARS-CoV-2 infection

In the phase II/III trial of the Pfizer COVID-19 vaccine, the vaccine was administered to a small number of people with serological evidence of previous SARS-CoV-2 infection. No specific safety issues were reported among these people. Overall efficacy was high when people who had had previous SARS-CoV-2 infection were also included for analysis. Efficacy was not reported separately for people who had previous SARS-CoV-2 infection.

Moderna COVID-19 vaccination in people with a past SARS-CoV-2 infection

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 thats 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 youre 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. Thats why you can still contract the new coronavirus and become ill if youre exposed to it shortly after getting your vaccine.

relatively weak immune response when given as just one dose. However, there was a stronger immune response when a second dose was added.

Why do you need this waiting period?

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The Change Is Not Yet Official

The change to the dosing schedule has not yet been finalized by the CDC.

According to Cameron, changing the dosing interval recommendations involves a rigorous process with multiple checks and balances across many institutions, regulatory centers, and scientific groups.

The vaccine scheduling dataset supporting any change needs to be of sufficient size and scope before changes can be approved and adopted, Cameron said.

What Is An Emergency Use Authorization

What Do I Need to Know About COVID

The FDA can issue an Emergency Use Authorization to allow the use of unapproved medical products in an emergency to diagnose, treat, or prevent serious or life-threatening diseases or conditions when specific criteria have been met, including that there are no adequate, approved, and available alternatives.

Manufactures submit a request for an EUA to the FDA which is reviewed, and a determination is made by the FDA about authorizing the EUA.

On Aug. 23, 2021, the FDA issued full approval of the Pfizer vaccine for those 16 and older. This full approval further indicates how safe and effective the vaccines are.

Under 18 years

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Adults Aged < 60 Years

Pfizer or Moderna COVID-19 vaccines are preferred over AstraZeneca in people aged < 60 years. This is based on the higher risk and observed severity of thrombosis with thrombocytopenia syndrome in people aged < 60 years compared with people aged 60 years. People aged 60 years are also at higher risk of severe illness from COVID-19, meaning the benefits of vaccination outweigh the very small risk of TTS.

However, AstraZeneca COVID-19 vaccine can be used in adults aged < 60 years if the person has made an informed decision based on an understanding of the risks and benefits. In outbreak settings, adults aged < 60 years should strongly consider AstraZeneca if they cannot access Pfizer or Moderna COVID-19 vaccines.1

There is a substantially lower rate of TTS following a second dose of AstraZeneca as compared to a first dose.

Registering Your Vaccination If You Got It Out Of The Province

If you received a COVID-19covid 19 vaccine outside of Ontario or Canada, you can register your vaccination by contacting your local public health unit .

You must provide proof, such as an immunization record or a proof of vaccination certificate to your PHU to be registered in the system.

If needed, you can book your second dose through:

  • the provincial booking system or calling the Provincial Vaccine Contact Centre
  • your primary care setting
  • public health units that use their own booking system

If you received both doses of a Health Canada authorized vaccine, you only have to provide proof of vaccination to your PHU. No other action is needed. If you received one or two doses of a COVID-19covid 19 vaccine not authorized by Health Canada, please contact your public health unit to see if you need any additional doses.

For more information, read the Ministry of Health COVID-19 Guidance for Individuals Vaccinated Outside of Ontario/Canada.

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Should Those Who Are Immunocompromised Continue To Take Precautionary Measures After They Get Vaccinated

Yes. People who are immunocompromised may have a reduced immune response to COVID-19 vaccines. They should continue to follow current preventive measures to protect themselves against COVID-19 until advised otherwise by their health care professional. Close contacts of immunocompromised people should also be strongly encouraged to be vaccinated against COVID-19 to protect these people.

Vaccine Types For Booster Doses

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The Comirnaty and Spikevax vaccines are approved by the Therapeutic Goods Administration and recommended by ATAGI as a COVID-19 booster dose.

You can have the Pfizer or Moderna vaccine as a booster dose regardless of which vaccine you had for your first 2 doses.

You can also receive the Vaxzevria vaccine if you:

  • cant have the Pfizer vaccine for medical reasons
  • had 2 doses of the AstraZeneca vaccine previously.

Read ATAGIs advice on the type of vaccine recommended for booster doses.

  • 1AstraZeneca can be given as a booster dose in some circumstances, see ATAGI’s advice.

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Why Is This Important

When the immune system first encounters a vaccine, it activates 2 important types of white blood cells.

First up are the plasma B cells, which primarily focus on making antibodies against the pathogen .

Unfortunately, this cell type is short-lived. Your body might be swimming in antibodies within just a few weeks. But without the second shot there is usually a rapid decline in antibodies against the pathogen.

Then there are the T cells, each of which identifies a particular pathogen to kill it.

Some of these memory T cells linger in the body for decades until they meet their target. This means immunity from vaccines or infections can sometimes last a lifetime. But you usually won’t have many of this cell type until there is a second exposure to that pathogen, which happens through the booster dose.

On second exposure to the same vaccine, the body can respond by creating a stronger immune response to fight the virus if required.

It is not yet known how long the COVID-19 vaccine protection will last. Clinical trials are currently happening to find out if we will need annual or longer booster doses to ensure long term immunity.

With new COVID-19 vaccine developments every day, its normal to have questions or concerns, and possibly feel hesitant about getting a vaccine. That’s why we’re providing accurate, evidence-based answers to questions about COVID-19 vaccines.

Do People Have To Receive Two Doses And Do They Have To Be The Same Type Of Covid

Yes, it is important that every person who receives a COVID-19 vaccine receive the full two-dose course of a vaccine. Both Pfizer and AstraZeneca require 2 doses to provide the best immunity. Pfizer doses are given at least 21 days apart. AstraZeneca doses can be given 4 12 weeks apart, but the Australian Technical Advisory Group in Immunisation recommend doses should be 12 weeks apart. When its your turn to get the COVID-19 vaccine, you will be able to make that equally important follow up appointment.

It is important you get the same type of COVID-19 vaccine. This is because the evidence from clinical trials shows this is effective and is what is approved for use by the Therapeutic Goods Administration .

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Persons With An Autoimmune Condition


It is recommended that an mRNA COVID-19 vaccine should be preferentially offered to complete the vaccine series in individuals in the authorized age group with an autoimmune condition.

A viral vector COVID-19 vaccine may be offered to individuals in the authorized age group with an autoimmune condition only when all other authorized COVID-19 vaccines are contraindicated. Safety data in these populations following vaccination with a viral vector vaccine are not available.


Although participants with autoimmune conditions who were not immunosuppressed were not excluded from trials, they constitute a very small proportion of trial participants and represent a very narrow range of autoimmune conditions. However, real-world evidence has become available.

Observational studies in individuals with autoimmune conditions indicate that the frequency and severity of adverse events in this population is comparable to that of individuals without autoimmune conditions and what was reported in clinical trials. The onset of new autoimmune disease or disease exacerbation following vaccination with mRNA COVID-19 vaccines was rare or comparable to the background incidence of these events in the general population.

The safety and efficacy of Novavax Nuvaxovid has not been established in individuals who have an autoimmune condition.

Refer to Immunization in Persons with Chronic Diseases in Part 3 for additional general information on autoimmune conditions.

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