INFLUENZA VACCINE MANUFACTURE: making flu shots

FLU VACCINE # 1. Above: Influenza virus vaccine manufactured using eggs: creation of reassortant. See all RKM flu images Original image is 4,000 x 4,000 pixels. The graphic shows an epidemic viral strain (purple virion) being introduced into embryonated (i.e. fertilised) chicken eggs. The green virion represents a standard strain that grows easily in chicken eggs (A/Puerto Rico/8/34 - A/PR8). These two types replicate alongside each other in an individual egg. As they copy themselves, their genes get jumbled together. This happens because influenza stores its genetic material in eight separate segments and a progeny virus can source segments from different parent viruses. The resulting hybrid virus strains (also called reassortants) are vetted and one that contains genes for the purple surface proteins but all the other genes from the green strain is chosen as the new vaccine strain. This vaccine strain (translucent purplish virions in the yellow cone) is then grown in millions of eggs. This process is done in triplicate for each of the selected wild strains (see graphic #2 below): FLU VACCINE # 2. Above: Trivalent Influenza virus vaccine manufactured using eggs. See all RKM flu images Original image is 4,096 x 4,096 pixels. Traditional influenza vaccine is manufactured using three potentially threatening strains of flu (as designated by WHO). In the graphic these are shown as blue, red and purple virions. The green virion represents a standard strain that grows easily in chicken eggs. The fate of the purple strain is shown in more detail (although the same process is happening in parallel with all three epidemic strains). The purple and green viruses are cultured together in eggs to create a reassortant (shown as small purple particles). This vaccine strain is then grown in millions of eggs. The vast amount of virus produced is illustrated as an array of purple particles emerging from the bottom layer of eggs. This latter process is shown for each of the selected wild strains (blue and red particle arrays). Ultimately, these three vaccine strains are treated to make them inactive (basically smashed up) and form the new (trivalent) inactivated flu vaccine for that year. This is a killed virus vaccine. A similar process is used to create a live virus vaccine but in this case the standard virus would be one that is weakened (attenuated) and grows at lower temperatures. FLU VACCINE # 3. Above: Influenza virus vaccine manufactured using eggs. See all RKM flu images Image measures 500 pixels across, original image is 4,000 x 4,000 pixels. FLU VACCINE # 4. Above: Influenza virus vaccine manufactured using eggs. See all RKM flu images Image measures 500 pixels across, original image is 4,000 x 4,000 pixels. INFLUENZA VACCINES: considerable effort is being devoted to create large quantities of vaccine to fight a potential bird flu pandemic. Vaccines rely on the immune system to fight the disease. A vaccine primes the immune system by exposing the body to antigens present on the infecting agent. Influenza vaccines have to be regularly updated because the influenza virus constantly changes its surface antigens. The flu virus is a moving target, antigenically speaking, and so vaccine manufacture lags viral innovation. The problem with vaccinating against a flu pandemic is that we do not know what the new pandemic influenza strain will be like. Avian influenza vaccines might not work against a novel pandemic viral strain. A vaccination program will require a huge investment of resources. There is a race on to develop vaccines very fast and one option is DNA vaccines. DNA vaccination works by introducing DNA that codes for the antigen. The host cells create copies of the antigen which provoke an immune response thereby priming the person's immune system against a future attack by the real pathogen.

Influenza A viruses: are covered by a characteristic array of spikes that project radially from the viral envelope. Beneath the envelope lies the matrix (M1 protein) which covers the viral genetic material (RNA).

Spikes: there are two kinds of spike: Haemagglutinin (Hemagglutinin) usually abbreviated as HA and Neuraminidase usually abbreviated as NA. There are several varieties of HA and NA designated by numbers e.g. the current bird flu is H5N1.

• Haemagglutinin: glycoprotein that forms a trimer (i.e. three molecules link together to form the spike). HA is involved in attaching the virus to the host cell and in causing the membranes of the virus and host to join (fuse) allowing entry of the viral genes.


• Neuraminidase: glycoprotein that forms a tetramer (i.e. four molecules link together to form the spike). NA is involved in releasing the virus from the host cell.

M2: this is a small protein that is embedded in the viral envelope. Four molecules associate together to create a channel through the envelope that allows protons to pass through. There are only a few such pores in each virus particle. The M2 proton channel is important during replication when it allows protons to enter the virion where the acidification is thought to loosen the matrix from the underlying RNP.

Envelope: the viral envelope is derived from the host cell plasma membrane when the virus buds from the cell.

RNP - ribonucleoprotein: consists of the genetic information of the virus wrapped up in protein. This combination of genetic material and protein is called the nucleocapsid. The genetic information is stored as single stranded -ve sense RNA. The full complement of genetic information is called the genome and in influenza A the genome is divided into eight segments. These segments are assumed to link together (possibly in an ordered fashion) when the virus assembles at the cell surface. Because the genome of influenza is segmented there can be a mixing of genes when two or more types of influenza infect the same cell and segments from several sources become jumbled together in the progeny virus. Such novel strains could lead to PANDEMIC INFLUENZA one of the greatest threats we currently face.