133 Molesworth Street
PO Box 5013
28 November 2022
+64 4 496 2000
By email: [FYI request #20907 email]
Tēnā koe Mr Hill
Response to your request for official information
Thank you for your request under the Official Information Act 1982 (the Act) received by Manatū
Hauora (the Ministry of Health) as a partial transfer from Te Whatu Ora (Health New Zealand)
on 14 November 2022 for information regarding the transmission of COVID-19. Please find a
response to your request below.
“1. Why did the The Ministry of Health and Te Whatu Ora state repeatedly that being
vaccinated reduced transmission of the COVID-19 virus?
2. What evidence was The Ministry of Health and Te Whatu Ora acting on when they
stated to Government and the New Zealand public that being vaccinated reduced
transmission of the COVID-19 virus?”
Information collated by Manatū Hauora about transmission is available on our website on the
COVID-19 Science news webpage here: www.health.govt.nz/covid-19-novel-coronavirus/covid-
In general (not COVID-19-specific), there are two mechanisms through which vaccines can
potentially reduce transmission:
1. Preventing infection of the vaccinated person (if a person is uninfected, they cannot
transmit the virus). This is measured in vaccine efficacy/effectiveness against infection.
2. Reducing the number of onward infections (if the vaccinated person does become
infected). This is measured by assessing the reduction in the number of transmissions to
contacts of infected individuals.
These two methods combine to provide a larger effect than either of them in isolation.
For the Pfizer vaccine, there is a substantial body available about its ability to reduce the
number of infections (and the subsequent effect on transmission through reduction of infection).
This data has been monitored by Manatū Hauora and is publicly available on our website on the
COVID-19 Science news webpage.
Although the effectiveness of the vaccine against infection reduces over time, an effect does
persist for a period after vaccination (for example it is estimated 50% of infections are prevented
at around four months after vaccination for individuals aged 18-59 years).Effects on onward
transmissions (that is, the ability of a vaccinated person to transmit on to other people) is
substantially more challenging to measure (and the results are harder to interpret) as there are
far fewer studies. The limited data that is available for Omicron on onward transmission after
infection (all vaccines, not limited to Pfizer) is available on the COVID-19 Science news
It should be noted that data for vaccine effectiveness (against infection and onward
transmission) for variants prior to Omicron have been monitored since trial data was first
released by Pfizer in 2020. Vaccine effectiveness against infection was generally higher for
previous variants than for Omicron.
I trust this information fulfils your request. Under section 28(3) of the Act, you have the right to
ask the Ombudsman to review any decisions made under this request. The Ombudsman may
be contacted by email at: [email address]
or by calling 0800 802 602.
Please note that this response, with your personal details removed, may be published on the
Manatū Hauora website at: www.health.govt.nz/about-ministry/information-releases/responses-
Nāku noa, nā
Interim Group Manager, Intelligence, Surveillance and Knowledge
Public Health Agency | Te Pou Hauora Tūmatanui
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