Influenza A (H1N1) Blog

We are in full production phase of vaccines against the Influenza A (H1N1), and some doses are already being distributed in the United States. However, if the virus was already circulating in May, why did it take so long to have the vaccine available? Understand why in this series of posts, beginning with the production of the vaccine:

Researcher examines eggs that will be inoculated with Influenza. © CDC 2008

There is a reason for us to be susceptible to Influenza every year: The virus mutates a lot. Since the genome of the Influenza is an RNA molecule, a viral polymerase is necessary to make a copy of it. Our cell is capable of duplicating the DNA, DNA>DNA, and producing RNA in the transcription, DNA>RNA, but we do not have enzymes to make RNA>RNA, and the Influenza needs to bring one with it. It is formed by the genes PA, PB1 and PB2. Different from our polymerases, the RNA polymerase of the virus has no error repair, so, when copying its genome, it changes various bases. These are the so-called mutations.

Identification of a new virus

Due to the mutations, the proteins of the Influenza vary a lot and cause the antibodies to fail in their recognition. Therefore, we need to produce new vaccines every year. Along with time, the immunization is lost, for we do not have cross-protection anymore against new lineages of the virus. Thus, the WHO promotes two annual meetings, one in the beginning and other in the middle of the year, prior to the winter of each hemisphere, a period in which the influenza cases are concentrated. In these meetings, researchers discuss which are the Influenza strains in circulation and which shall be in the vaccine to be produced.

As the production process takes long, approximately six months are necessary to “guess” – based in monitoring and statistics, of course – which will be the most important lineage of the virus in the future. Choose the wrong virus implies in loosing time and money producing an ineffective vaccine and, most important, more deaths caused by the influenza.

The vaccine virus

Once the variants that will go to the vaccine are chosen, generally one Influenza A H1N1, one A H3N2 and one Influenza B, both Influenza A need to be adapted to grow in eggs. Not necessarily the chosen virus will grow well in the egg tissues, so, it needs to be hybridized with a lineage of good growth. Generally, the lineage used is the same since the 1970’s, the lineage A/PR8/34.

This step it spend time and tests. Both virus, the vaccine and the adapted to grow in eggs, are added to the cells, and in it, will form hybrid viruses. Here, the key point is to choose a virus that grows well in eggs and produces the immune response against the circulating virus. Several tests are necessary to ensure that the hybrid virus is not dangerous, that it grows well and that it immunizes against the right proteins. The intention is not to produce a vaccine against the virus A/PR8/34, but against the lineage determined by the board of specialists of the WHO.

Production

The production process of Influenza vaccines remains almost the same since the 1950’s, with the use of embryonated eggs. To produce the virus to be inoculated in the people, it is necessary to have a sterile and favorable environment to the Influenza. The egg offers both. As the embryo still does not have the immune system developed, there is no response against the virus, and its tissues and husk ensure that the interior is isolated and contains only cells of the chick.

Theoretically, it seems very simple. Now imagine that, in addition to having to deal with hundreds of thousands of eggs within a controlled and non-contaminated environment, it is necessary to use the eggs in the period. Very young eggs do not have the allantoidal cavity – place where the virus will grow – well formed and very old eggs already have the embryo too developed, consequently, immunity. Due to that, the eggs cannot be simply stored. They need to be brought continually in the right phase, between 7 and 19 days, be opened for the inoculation with the virus, closed and incubated for the right period.

Such details cause the production to be slow and costly, hard to scale for a larger production and with a large inertia. If the wrong virus is inoculated, it may be too late to start again. After the first doses are produced, the tests are initiated to verify if the vaccine will be effective.

Preparation

Another essential step for the development of the vaccine is the inactivation and purification of the virus. The Influenza needs to be completely inactivated – dead is not a concept that applies to viruses – to not cause infection to those who receive the vaccine. Fever or headache after vaccination are caused by our immune response to the pieces of the virus, or antigens, in the vaccine. There is no development of the virus.

The purification ensures that the right proteins will be present in the vaccine, and that there will not be contaminants as bacteria or egg tissues, which may cause infections, allergies or immunization against the wrong antigens. It should also ensure that the proteins of interest, the viral antigens, will be in the concentration necessary for our body to respond with the expected production of antibodies.

The next text will deal with the distribution of the vaccines.

Source:

[1] Gerdil, C. (2003). The annual production cycle for influenza vaccine Vaccine, 21 (16), 1776-1779 DOI: 10.1016/S0264-410X(03)00071-9
[2] Osterholm, M. (2005). Preparing for the Next Pandemic New England Journal of Medicine, 352 (18), 1839-1842 DOI: 10.1056/NEJMp058068