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Moderna mRNA-1273 vaccine against COVID-19: administration and dose schedules

The COVID-19 pandemic has caused significant morbidity and mortality throughout the world, as well as major social, educational and economic disruptions.
There is an urgent global need for effective and safe vaccines and to make them available at scale and equitably across all countries.

The mRNA-1273 vaccine against COVID-19 developed by Moderna ( Moderna COVID-19 vaccine ) has been shown to have an efficacy of 94.1%, based on a median follow-up of two months.
High efficacy was maintained across all age groups ( above 18 years ), and was not affected by sex or ethnicity.

The data reviewed by WHO at this time support the conclusion that the known and potential benefits of mRNA-1273 outweigh the known and potential risks. As sufficient vaccine supply will not be immediately available to immunize all who could benefit from it, countries are recommended to use the WHO Prioritization Roadmap and the WHO Values Framework as guidance for their prioritization of target groups. When vaccine supplies are very limited ( stage I in the WHO Prioritization Roadmap ), in settings with community transmission, the Roadmap recommends that priority be given initially to health workers at high risk and older people with and without comorbidities.
Protecting high-risk health workers has a threefold purpose: (i) to protect the individual health workers; (ii) to protect critical essential services during the COVID-19 pandemic, and (iii) to prevent onward transmission to vulnerable people.
Protecting older people will have the greatest public health impact in terms of reducing the number of deaths. As more vaccine becomes available, additional priority groups should be vaccinated as outlined in the WHO Prioritization Roadmap, taking into account national epidemiological data and other relevant considerations.

Intended use

Persons aged 18 years and above


The recommended schedule is two doses ( 100 μg, 0.5 ml each ) given intramuscularly into the deltoid muscle. An interval of 28 days between doses is recommended. If the second dose is inadvertently administered less than 28 days after the first, the dose does not need to be repeated.
If administration of the second dose is inadvertently delayed it should be given as soon as possible thereafter, according to the manufacturer’s instructions. It is currently recommended that individuals receive no more than two doses in total.

Considerations for modifications to vaccine dose schedules

WHO acknowledges that a number of countries face exceptional circumstances of vaccine supply constraints combined with a high disease burden.
Some countries have therefore considered delaying the administration of the second dose to allow for a higher initial coverage. This is based on the observation that efficacy has been shown to be 91.9%, starting 14 days after the first dose, with a median follow-up time of 28 days.

There appears to be protection against COVID-19 disease following one dose; however, there is insufficient information about longer-term protection beyond 28 days after a single dose, as most trial participants received two doses.
It is of note that neutralizing antibody responses were modest after the first dose and increased substantially after the second dose.

Countries experiencing such exceptional circumstances may consider delaying the administration of the second dose as a pragmatic approach to maximizing the number of individuals benefiting from a first dose while vaccine supply continues to increase.

WHO’s recommendation at present is that, if judged necessary, the interval between doses may be extended to 42 days. The evidence base for this extension is not strong, but this was the longest interval for any participants in the primary efficacy analyses of the phase 3 trial, though the great majority received the second dose after a shorter interval. It is anticipated that additional data on extending the interval will become available shortly from use of the vaccine in public health vaccination programmes.

Countries should ensure that any programme adjustments to dose intervals do not affect the likelihood of receiving the second dose of the same vaccine.
WHO does not recommend halving the dose to 50 μg until supporting evidence is available.

Booster doses

There is currently no evidence on the need for a booster dose or booster doses of the vaccine after the current two-dose vaccine series is complete.

Interchangeability with other vaccines

No data are available on the interchangeability of this vaccine with other mRNA vaccines or other COVID-19 vaccine platforms. It is currently recommended that the same product should be used for both doses. If different COVID-19 vaccine products are inadvertently administered in the two doses, no additional doses of either vaccine are recommended at this time.

Co-administration with other vaccines

There should be a minimum interval of 14 days between administration of this vaccine and any other vaccine, until data on co-administration with other vaccines become available. ( Xagena )

Source: WHO - World Health Organization, 2021