Updated January 14, 2021.


What is a vaccine?

A vaccine is a substance used to stimulate the production of antibodies and provide immunity against one or several diseases without causing the disease. Vaccines are in a category of substances known as antigens.

What are antigens?

An antigen is a substance foreign to the body that, when recognized by the body’s immune system, brings about a response to rid the body of the antigen and either prevent or minimize illness.  These responses, called immune responses, include directly “killing” the antigen, bringing about the production of antibodies to neutralize the antigen, and producing “memory cells” so that if the antigen is detected in the future it can be destroyed by the immune system.

What are the different types of vaccines for COVID-19?

Several different pharmaceutical companies started working to develop a COVID-19 vaccine in the spring of 2020.  FDA’s Center for Biologics Evaluation and Research [CBER] ensures that FDA’s rigorous scientific and regulatory processes are followed by those who pursue the development of new vaccines.  The vaccines that have been made public include the mRNA vaccines made by Pfizer and Moderna. Adenoviral vaccines made by Astra Zeneca and Johnson and Johnson may be ready early in 2021.  The Pfizer and Moderna vaccines have completed successful trials with thousands of volunteers, have been reviewed and approved by the FDA for immediate emergency use, and are currently the only vaccines available to the general public.

What is an mRNA vaccine?

This type of vaccine uses viral messenger RNA (mRNA) to teach the immune system to recognize viruses as antigens.  mRNA, found in all cells, provides cells with instructions on how to make proteins (among other functions).  In the case of activating the immune system, the mRNA instructions cause the cell to make a protein that is very similar to the virus or one of its parts. Once this protein is made and “displayed” on a cell surface the body then recognizes this altered cell as foreign (an “antigen”) and begins to produce antibodies against the antigen. This technology DOES NOT use a live or weakened form of the virus, nor does it affect the nucleus or DNA of the cell.  These mRNA vaccines do not and cannot infect those who receive them with COVID-19. While mRNA vaccines represent a new technology, using mRNA to produce antibodies is not new; this approach has been studied in laboratories for many years.

How do the COVID-19 mRNA vaccines work?

The COVID-19 mRNA vaccine is first injected into a muscle in your upper arm. The vaccine then enters nearby cells and instructs them to make a piece of the COVID-19 “spike protein” that plays a role in anchoring the virus to respiratory and other body tissues.  Once the mRNA instruction is received by your cells, those cells start manufacturing the spike protein and display it on their surface.  The presence of the “foreign” spike protein on the surface of the cell causes your body to produce antibodies against the spike protein.  Should you become exposed to the virus, these antibodies will recognize the COVID-19 spike protein and fight the virus or minimize its infectiousness.

What is an adenoviral vaccine?

An adenoviral vaccine uses an adenovirus -- common viruses that typically cause colds or flu-like symptoms -- to activate an immune response.  This technology is the basis for many vaccines that are already in widespread use.  These vaccines insert a gene that codes for a protein into an unrelated adenovirus that has been modified and rendered harmless. Once rendered harmless this adenovirus with the inserted gene will not and cannot infect anyone with COVID-19.  Once administered in the vaccination, the adenovirus attaches to a cell surface, moves into the cell, enters the cell nucleus, and incorporates into the cell DNA.  This causes the cell nucleus to “read” the inserted gene and instructs its natural mRNA to begin making the protein instructed by the inserted gene. 

How do the adenoviral COVID-19 vaccines work?

The gene for the coronavirus “spike protein” is inserted into an adenovirus that has been modified to render it harmless (it cannot cause COVID-19).  Once administered into a muscle in the upper arm this modified adenovirus enters a cell, travels to the nucleus, and inserts the gene for making the spike protein into the host cell DNA.  The host cell “reads” the gene for the COVID-19 spike protein and copies the instructions for making the spike protein onto natural mRNA.  The mRNA then directs the cell’s protein-building structures to produce the COVID-19 spike protein.  The manufactured spike protein travels to the surface of the cell where it is recognized by the immune system as “foreign” and starts producing antibodies against the spike protein.  Should you become exposed to the virus, these antibodies will recognize the COVID-19 spike protein and eradicate the virus or minimize its infectiousness.

Both types of vaccines use mRNA – how are they different?

The Pfizer and Moderna mRNA vaccines are composed of mRNA containing the instructions for making the COVID-19 spike protein so that once the vaccine is taken into a cell the protein building instructions are already in place and spike proteins can be made by the cell protein building structures.

The adenoviral vaccines contain the instructions for building the spike protein on a gene that has been incorporated into a modified adenovirus.  Once this vaccine enters the cell it travels to the cell nucleus where it inserts the gene for making the spike protein into the cell DNA. The cell DNA then transfers these instructions to its own mRNA. This mRNA then leaves the cell nucleus and travels to the cellular structures that build the spike protein.

For more information including drawings showing how adenoviral and mRNA vaccines work, visit:

New York Times interactive, Moderna Vaccine
New York Times interactive, Astrazeneca Vaccine
USA Today, How New RNA Technology Was Used to Create COVID-19 Vaccines


When will the vaccine be available and where will I get it?

The Pfizer and Moderna vaccines have received emergency authorization from the FDA for general public use.  These vaccines are currently being given first to health care workers and residents and staff in long term care facilities.  The state of NH is following a schedule coordinated by NH Department of Health and Human Services that divides the population into multiple phases for the vaccination program, with vaccinations for the general public expected in late spring. This phased approach is subject to change, based on vaccine and vaccinator availability:

VACCINATION SCHEDULE as of January 14, 2021

NH DHHS Vaccination Scheduled as of Jan 14, 2021

The timeline for widespread access to a COVID-19 vaccine is expected to be approximately 6-12 months, according to health officials. Seacoast health care networks are asking that residents be patient as they wait to learn COVID-19 vaccine distribution information. Please do not call health care offices, fire or police departments, emergency medical services or local officials. If you have questions, call 211 or email

Each state and its public health department makes the final decision on who is eligible for the vaccine and when they can receive the vaccine.  To learn about the vaccine rollout in NH, click here.

Where will I get the vaccination?

In the first phases, the state is setting up vaccination distribution programs. The wide public distribution of the vaccine will be handled much the same as flu shots -- through your healthcare provider, CVS and Walgreens.

How much will it cost to get the vaccine?

At the present time all approved vaccines are provided at no cost [your tax dollars funded the vaccine research and production so the vaccine itself is “free”].  There may be cost to administer the vaccine depending on where you are vaccinated.  This cost should be covered by your health insurance.  If you are uninsured, the fee for giving the shot will be covered by the Health Resources and Services Administration’s Provider Relief Fund.

Does it make a difference which vaccine I receive?

Currently both the Moderna and Pfizer mRNA vaccines are reported to be about 95% protective – meaning that almost everyone who receives the vaccine is protected from getting sick with COVID-19, and it reduces the severity of the infection. 

As the trials continue the percent protection may change and research will determine if the vaccine completely prevents the disease, how long it provides protection, and if it protects against spreading the disease should you be infected with COVID-19.

Can I get one dose of one of the vaccines and the second dose of another a different vaccine?

No – while both the Pfizer and Moderna mRNA vaccines require two doses, the manufacturing process of each vaccine was different and proprietary for each company.  Since the vaccines differ in composition, storage, and time between doses, people must get the same vaccine for both doses

What if I miss the second vaccination?  What should I do?

Each vaccine that requires two shots for full immunity has its own schedule for the second vaccination.  The two currently approved vaccines are: 21 days between shots for Pfizer and 28 days between shots for Moderna.  It is important to know which vaccine you received to know when to schedule your second vaccination.

The clinic, doctor’s office, or other vaccination location should schedule your second shot at the time of your first shot.  Be sure to write this down in a place where you will remember the next appointment.  Should you miss your appointment or need to reschedule for any reason be sure to get the second shot as soon as possible to ensure the benefit of full immunity.  At this time, it is not recommended to begin over – just get the second shot as soon as you can.


NH DHHS Vaccine Comparison 12/31/20

For the complete Update (12/31/20) from NH DHHS, click here.

Is the vaccination painful? 

The vaccination involves an injection into your upper arm with a thin needle. The shot itself will feel the same as other vaccinations you have received.

What are the side effects?

Both the Pfizer and Moderna trial participants reported minor side effects common to many vaccinations including a sore arm or feeling poorly, fatigue, or tired for a day or two after the shot. Other reported side effects included headache, fever and chills, and other muscle aches/pain primarily after the 2nd shot that lasted a day or two.  Some vaccine trial participants treated these side effects with pain medication.  The percentage of participants experiencing these side effects depend on the vaccine administered.  For specific percentages detailed in the report, click here.

There have been isolated reports of more severe side effects including allergic reactions.  It is important that you discuss getting the vaccine with your health care provider to determine if you are at risk for a more severe reaction.  It is also recommended that you plan to stay for at least 15-30 minutes after receiving the vaccine to monitor for a serious side effect and to receive the vaccination in a place capable of providing prompt emergency care.

What should I do if I have a bad reaction to the vaccine?

If you have a bad reaction, you should notify your primary care provider immediately.  If you are having trouble breathing, notice any sudden swelling (especially of your face or tongue), or feel faint after you have received the vaccine and left the facility, call 911 for immediate emergency care.

The CDC and FDA encourage the public to report possible side effects (called “adverse events”) to the Vaccine Adverse Event Reporting System (VAERS)external iconexternal icon. This national system collects data to look for adverse events that are unexpected, appear to happen more often than expected, or have unusual patterns of occurrence. Reports to VAERS help the CDC monitor the safety of vaccines. Safety is a top priority.

The CDC is also implementing a new smartphone-based tool called “v-safe” to check-in on people’s health after they receive a COVID-19 vaccine. When you receive your vaccine, you should also receive a v-safe information sheet telling you how to enroll in v-safe. If you enroll, you will receive regular text messages directing you to surveys where you can report any problems or adverse reactions you have after receiving a COVID-19 vaccine.

I have a history of allergies – should I get the vaccine?

Since its public rollout both vaccines have been associated with an immediate allergic reaction in a very small number of people.  These reactions have occurred within the first 30 minutes after receiving the shot; for this reason, those with severe anaphylaxis to anything [drug, food, insect bites, etc.] should be informed of risk and monitored for 30 minutes rather than 15 minutes after vaccination to be sure you do not have a serious allergic reaction.

Right now, it is highly recommended that persons who have had an anaphylactic reaction to any drug, food or other vaccine NOT receive the vaccine". Both vaccines have only one contraindication in the respective labels, and that is for known history of a severe allergic reaction to any component of the vaccine (so, neither includes severe reactions to other products as a contraindication). The DHHS guidance says for those with severe anaphylaxis to anything the patient should be informed of risk and monitored for 30 minutes rather than 15. It does not say they shouldn't get the vaccine. (Underlining here is mine, for emphasis)

If I have had COVID-19 do I need to get a vaccination?

It is not known how long immunity lasts following recovery from COVID-19.  The current recommendation is to discuss getting the vaccination with your health care provider. It is suggested that a person who has recovered from COVID-19 wait 90 days before receiving the vaccine.

I’m pregnant and/or breastfeeding – should I get a vaccine?

The vaccine has not been tested in pregnant women or women who are breastfeeding.  It is recommended that you discuss vaccination with the person providing your pregnancy or breastfeeding care.

I have chronic health problems that put me at higher risk should I get COVID-19, should I get the vaccine?

We know that those with chronic health conditions including asthma, COPD, diabetes, heart disease, and obesity are at higher risk of becoming seriously ill should they contract COVID-19.  Persons with pre-existing conditions are more likely to need hospitalization, oxygen support, and sometimes intensive care including a mechanical ventilator. The vaccine trials have included people with pre-existing conditions for exactly this reason; and the vaccines have been demonstrated to be safe in trial participants with pre-existing conditions. It is important to discuss with your primary care provider your potential risk should you develop COVID-19 and the benefit you might receive from vaccination.

I don’t want to get a vaccine, what other ways can I protect myself from contracting COVID-19?

A good place to start for accurate information on your risks, whether or not you choose to become vaccinated, is with your primary care provider.  Your PCP has all the health information you’ve shared available to carefully and thoughtfully help you consider your benefit and risk for vaccination.

Whether you choose to be vaccinated with a COVID-19 vaccine or not, you should continue to follow all recommendations for avoiding infection and if infected, not spreading the infection to others.  Those recommendations are often referred to as the 3 C’s: avoid crowded places, contact with infected persons, and closed spaces and, the 3 W’s: Wear a mask, Wash your hands frequently, and Watch your distance—maintaining 6’ apart from others (also called physical distancing).


Once vaccinated how long does it take to be protected?

In general, it takes 7 to 14 days after the last vaccine shot to have robust immunity. (Pfizer and Moderna vaccines each require two shots).  Before that time, you may have some protection against COVID-19 but it is not possible to predict how protected you are before completing the vaccination schedule. 

Once I’m vaccinated, do I still need to wear a mask?

Yes. Mask wearing remains one of the best ways to prevent the spread of COVID-19.  While the vaccines have been shown to keep a vaccinated person from becoming ill with COVID-19 it is not yet known whether the vaccine prevents the spread of the virus.  It is possible that a vaccinated person could harbor the virus in his/her nose and spread the virus even though he/she does not become ill.  Further research is being conducted to determine if the vaccine also prevents COVID-19 spread. The Portsmouth Mask Ordinance is in effect through June 30, 2021 and the NH statewide Mask Mandate is in effect through February 5, 2021.

The NH Department of Safety notes (January 11, 2021): 

It remains possible that people who are fully vaccinated or previously infected could still acquire asymptomatic SARS-CoV-2 infection, or attenuated (milder) COVID-19. Therefore, even people who are fully vaccinated or previously infected need to continue to practice physical distancing, avoid social groups and gatherings, and wear face masks at all times when in public places and facilities. Healthcare providers should continue to follow all recommended infection control and personal protective equipment (PPE) guidance. 

Once I have received the full vaccine will I need a booster shot?  Will I have to be vaccinated every year, like with the flu shot?

At this time, it is not known how long immunity will last not only from the vaccines, but also for those who developed COVID-19 and natural immunity from having the disease.  As the vaccine trials progress and more information is collected, we will have a better idea as to the length of protection and/or the need for additional shots.


Do you have additional questions about the COVID-19 vaccinations in NH?


For more information on the vaccines, visit: