Can I have a COVID-19 vaccination before a CT scan?

It is important to advise your oncologist or radiographer if you have received the COVID-19 vaccine recently. This is because the vaccine can cause the lymph nodes in your armpit and neck to swell which can be detected by CT scans used to diagnose and monitor cancers.

This is particularly detected by FDG PET/CT scans, in which you are given a contrast medium containing a type of radioactive sugar that is taken up by active cells. When an immune response to a vaccine takes place, the cells in the lymph nodes near the injection site become very active and take up a lot of this sugar. Depending on the type of cancer, you may be able to request the injection on the opposite side to your tumour. If possible, have the vaccination at least 2 weeks before a scheduled scan or as soon as you can afterwards. Do not delay any treatment.

Can I receive the COVID-19 vaccine even though I have a compromised immune system or am receiving treatment for cancer?

Many people take medication that suppresses their immune system, especially for the treatment of cancer, severe asthma, autoimmune diseases or following organ transplantation, or have medical conditions that can affect the immune system, such as HIV infection or kidney failure.

These conditions put you at increased risk from COVID-19, and although you may not respond as strongly to the vaccine as someone with a fully functioning immune system, it is safe for you received COVID-19 vaccine and it will provide some protection against COVID-19, particularly against severe and life-threatening disease.

It is important and safe for those receiving active treatment with immunosuppressive medications to have the COVID-19 vaccine. If you are severely immunocompromised, it is recommended to talk to your GP or specialist to discuss the optimal timing for vaccination before the vaccine appointment. Ideally, vaccination should be conducted prior to any planned immunosuppression.

It is also important for the people around you, in your household, to have the vaccine when it is offered to them to widen your protection.


For information about Cancer care and COVID-19 vaccine see Te Aho o Te Kahu (Cancer Control Agency) information here.

How many doses of COVID-19 vaccine should I have? I already received a COVID-19 vaccination overseas.

If you were partially vaccinated overseas with one dose of Comirnaty (Pfizer/BioNTech) vaccine, you will need to have another dose at least 21 days after your previous dose. There is no maximum time limit between doses, so you do not need to repeat the first dose or receive a third dose.

If you received one dose of different vaccine (for example, COVID-19 vaccine AstraZenaca/Vaxzevria/Covishield or the Moderna mRNA COVID-19 vaccine), the current recommendation is to have one dose of the Comirnaty vaccine when it becomes available for your priority group at least 4 weeks after your first vaccine. These vaccines are not interchangeable, but you are likely to have a good response to just one dose. If you received one dose of the Janssen/Johnson & Johnson vaccine, you are considered fully immunised and do not require any further doses of COVID-19 vaccine.

Can I delay receiving my second dose of Comirnaty?

It is recommended to have the second dose of Comirnaty™ at least 21 days after the first dose. A delay for longer than 21 days is not considered to be a problem in terms of how you will respond to the second dose.

It is not yet known, for how long the first dose provides protection. If you are at risk of exposure to SARS-CoV-2, it is advisable to have the second dose when recommended. During clinical trials, the vaccine efficacy against symptomatic COVID-19 between the first and second doses was around 50% compared with 90% within 2 days of the second dose increasing to 95% after a week. Recent real-world data has shown that protected against SARS-CoV-2 infection was around 62 to 91% from 14 days after dose one and 68 to 97 % from 14 days after dose two in frontline workers. 

Can I have the COVID-19 vaccine if I am allergic to latex?

Comirnaty™ is latex-free. The vial stopper is made with synthetic rubber (bromobutyl), not natural rubber latex.

Is the Comirnaty vaccine safe and effective for people living with HIV?

The vaccine has been through rigorous testing to ensure safety and efficacy and is now being used widely overseas without any serious concerns appearing. People with HIV were included in clinical trials though efficacy and safety data specific to this group are not yet available.

With some vaccines people living with HIV can produce a weaker immune response. People living with HIV are encouraged to be vaccinated. People with HIV were included in clinical trials for the Pfizer vaccine, although the data specific to this group is not yet available there are no safety concerns.

Based on what we know about people living with HIV and their response to other vaccines:

  • those with a suppressed viral load are likely to have some protection from the COVID-19 vaccine
  • they may have a weaker response to some vaccines, including the COVID-19 vaccine

For people who are newly diagnosed and starting HIV treatment are advised to take advice from their specialist about the timing of their vaccination. Any medication being taken for HIV is not expected to change how effectiveness of the COVID-19 vaccine. The vaccine will not affect HIV medications.​

If you had the virus and recovered, will you still be able to or need to get the vaccine?

Vaccination is being offered to people who have and have not had SARS-CoV-2 infection previously.

Data from clinical trials and from countries with a lot of COVID-19 cases have shown the vaccines to be safe and effective in this group of people. It is expected that the vaccine will boost the immune response and provide good protection for those who have previously had SARS-CoV-2 infection. Start your vaccination course at least 4 weeks after you have recovered. For more information, please click here.

Can COVID-19 vaccines be safely given to frail and elderly people?

There are no safety concerns around giving COVID-19 vaccine to older and frail adults. Multiple COVID-19 vaccine candidates have shown to protect against severe disease in older age groups.

A single dose of COVID-19 vaccine substantially reduced (over 70%) the risk of COVID-19-related hospitalisation in elderly, frail patients with extensive co-existing conditions in the UK. By 2 weeks after the second dose effectiveness against symptomatic COVID-19 in adults aged over 70 years was 85-93%. This is important, as increasing age is a risk factor for severe COVID-19.

Following reports of deaths of frail, elderly adults in residential care facilities after COVID-19 vaccination, independent reviews by both the CDC and the WHO concluded that the mortality rate in this population is typically high and a substantial number of deaths will occur coincidentally following vaccination. For further information, click here.