Influenza vaccines are used to immunise people against a flu virus that is in circulation among the population. They are one of the most effective means for preventing people from becoming ill and for controlling the spread of infection.
Pandemic influenza vaccines need to be specifically developed against the strain of virus causing the pandemic. Because the strain of flu virus causing a pandemic is not known before a pandemic is imminent, pandemic influenza vaccines can only be prepared once a pandemic has started and the exact strain of flu virus responsible can be identified.
Seasonal flu vaccines designed to provide protection against seasonal flu are not used during a flu pandemic as they are unlikely to provide protection against pandemic flu.
In the EU, the European Commission and EMA have put procedures in place to speed up the assessment and authorisation of vaccines for use during a flu pandemic. There are two main routes of authorisation for pandemic influenza vaccines, although other options exist depending on the level of emergency:
EMA offers a specific type of marketing authorisation to allow a vaccine to be developed and authorised before an influenza pandemic.
Such vaccines normally contain a strain of bird flu virus (for example A/H5N1) that few people in the world have already been exposed to and that could potentially cause a pandemic.
The vaccines are tested to determine whether they will protect people against the virus strain that they contain. Often more than one virus strain is tested, in order to obtain as much information as possible on how the vaccine works, allowing for better preparedness.
Pandemic preparedness vaccines can be authorised but not marketed before an influenza pandemic.
In the event of a pandemic, once the virus strain causing the pandemic is identified, the manufacturer can include this strain in the authorised pandemic preparedness vaccine and apply for the vaccine to be authorised as a 'final' pandemic vaccine.
The authorisation of the final pandemic vaccine can be very fast as EMA's scientific committees have already assessed the vaccine safety and efficacy with other potential pandemic strains.
Four pandemic preparedness vaccines are currently authorised in the EU, which can be modified into pandemic influenza vaccines in a future pandemic:
The emergency procedure allows for fast-track approval of a new vaccine developed once an influenza pandemic is declared.
Authorisation of these pandemic vaccines is faster than a normal vaccine, because EMA assesses the information submitted by the manufacturer in an accelerated timeframe, taking around 70 'active' days instead of the usual 210.
However, the emergency procedure is considerably slower than the procedure required to activate a pandemic preparedness vaccine.
This procedure allows vaccines authorised for use against seasonal flu to be modified for use against pandemic flu, by swapping the seasonal virus strains with the pandemic strain.
This procedure can only be considered in selective circumstances where there is scientific evidence suggesting that the modified vaccine could provide protection against pandemic flu.
Zoonotic influenza vaccines are intended for immunisation during outbreaks of influenza coming from animals, including when public health authorities anticipate a possible pandemic caused by the virus strain or a similar strain.
The zoonotic flu vaccines currently available contain the virus subtype A/H5 (bird flu) because health experts believe that this strain could cause a future flu pandemic and is responsible for recurrent outbreaks.
The following zoonotic influenza vaccine are authorised centrally in the EU:
The Zoonotic influenza vaccine Seqirus contains a A/H5N8 strain matching the currently circulating clade 2.3.4.4b to ensure protection.
The Aflunov and Celldemic vaccines contains A/H5N1 strains belonging to older clades no longer circulating, so they are not expected to protect but if required they can be modified rapidly to match circulating viruses.