Vaccine Underdose : What Should You Watch Out For?

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A potential problem COVID-19 vaccination is getting an underdose. Basically, less vaccine than what we are supposed to get.

Find out what vaccine underdose is all about, and how to avoid it!


Vaccine Underdose : What Is It?

A vaccine underdose is what happens when you receive less than the recommended dose of a vaccine.

This can happen by accident, or intentionally, but the end result is the same – you may end up with insufficient vaccine, or none at all.

Recently, two people reported that they received an underdose of the AstraZeneca COVID-19 vaccine. Anoogrehan Manoharan noticed it when he looked back at a video he took.

In his case, it seems pretty obvious that he received a vaccine underdose. He received a second vaccination – the full recommended dose four days later.


Vaccine Underdose : How Could It Happen?

There is always the possibility of intentional underdose by someone who is secretly anti-vaccination.

But accidental vaccine underdose can happen, especially in high-volume vaccinations.

Injection Volume Mix-Up

Different COVID-19 vaccines may have different injection volumes, as the table below shows.

This error can happen in vaccination centres that have more than one COVID-19 vaccine at hand

Of course, this obviously did not happen at the AstraZeneca vaccination centre, because they only deal exclusively with the Vaxzevria vaccine.

Vaccines Dose Volume
Pfizer COMIRNATY 0.3 ml
AstraZeneca Vaxzevria 0.5 ml
Sinovac CoronaVac 0.5 ml

Preparation Error

Some COVID-19 vaccines – like the Pfizer vaccine – must be mixed with saline and then drawn out into syringes for administration.

It has happened before that the vial was mistakenly filled with saline TWICE, leading to highly diluted doses.

This can happen if one staff member pre-fills the vials with saline, but is called away; and another staff member continues but does not realise that the vials have already been filled with saline.

Vaccine Underdose : What Should You Watch Out For?

Accidental Wastage

The nurse or doctor may have accidentally depressed the plunger while handling the syringe, without realising it.

This could happen while switching needles, or just before injecting it into the vaccine recipient.

They are supposed to check before injecting the vaccine, but mistakes can happen, especially if they are tired or overworked.

Low Dead Volume Syringe

To extract the maximum number of doses per vial, healthcare workers are using special low dead-volume (LDV) syringes.

These LDV syringes have longer plunger heads (the black rubber part). What we may think is just 0.3 ml is, in reality, 0.5 ml on an LDV syringe.

This may mislead people into thinking that they received less than the actual dose of the vaccine.

Low Dead Volume Syringe reading


Vaccine Underdose : How To Prevent It?

There are a few ways to prevent vaccine underdose.

  1. Use only one vaccine at each vaccination centre.
  2. If a vaccination centre should offer multiple vaccine options, then vaccination teams should be exclusively trained with one vaccine and not switch between vaccines.
  3. Vaccine doses should ideally be pre-filled and labelled (with date, time of preparation and recommended volume) and shown to the vaccine recipient before administration.
  4. Vaccine recipients should ask to see the syringe, and double-check the volume and preparation date, before receiving the vaccination.

Vaccine Underdose : What Should You Watch Out For?

  1. Vaccine recipients should also ask to record a video of the vaccination process.
  2. After the vaccine dose is injected into the recipient, the empty syringe should be shown to the vaccine recipient.
  3. If manpower permits, a third person – nurse or compliance officer – should be present to witness and help double-check the vaccine dose in each syringe, as well as the vaccination process.


Vaccine Underdose : What Should You Do?

If you believe you received an underdose of your COVID-19 vaccine, you should reach out to the healthcare provider who administered the vaccine.

Ideally, you should be vaccinated again with the correct dose; or a “top-up dose”, if they are able to determine the shortfall.

Here in Malaysia, you can reach out to the ProtectHealth Corporation – a private entity created by Malaysia Health Ministry to manage the national COVID-19 vaccination programme.


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