The race is on … vaccines vs variants. The global response will determine the winner18/02/2021
Boris Johnson’s call for wealthy nations to share Covid vaccines more equitably with poorer countries was vital. The warning from the WHO that “no-one is safe from Covid till all are safe” is a truism with major implications.
Viruses are considered one of the earliest creations of primitive evolutionary mechanisms. They are not ‘organisms’ with the capacity to reproduce themselves. Instead, they are composed of the blueprints for their reproduction that they must provide to a ‘factory’ that can follow the instructions and produce copies of the virus.
Like all viruses, SARS-Cov-2 attaches to and invades a cell that is capable of reproducing itself and diverts the production process to make copies of the invading virus.
Under evolutionary pressures viruses have realised it is not a good idea to simply clone themselves, i,e. make identical copies of themselves. Viruses constantly experiment to see if they can improve their capacity to invade hosts. It’s a random process so some changes may result in an inferior model but some ‘variants’ may result in a superior version. Change is also important as the host cells they invade may belong to an entity capable of making an immune response to the virus. Looking different is a good tactic.
The SARS-Cov-2 virus is known to have infected 110 million people, killing 2.5 million of those infected. As many people infected and infectious have few or no symptoms and testing regimens vary greatly, it is estimated that the real figure is likely to 20 times greater than that actually measured. Of course, with this virus multiplying billions upon billions of times, it is going to produce variants, some of which will provide it with new advantages.
Our pandemic is the result of these viruses developing a mechanism for attaching to specific cells lining the airways, mouths, noses and eyes of humans. All share a structure known as an ACE-2 receptor. This is a lock that, if opened, would allow a SARS virus to gain entry to cells in which it could multiply. Through trial and error the SARS virus has produced variants that have on their surface a ‘spike protein’. This is the key that will fit into the lock on the human cells described. Part of this spike protein can cut a hole in the cell to which the virus has attached, allowing invasion to occur.
Over the past 12 months viral variations on a theme have produced at least four new models with an improved capacity to bind to ACE-2 receptors. Imagine you had a key for a lock on a door. The lock and key were not perfectly aligned but you could get the door open with a few attempts and some patience. Imagine you get a replacement key that is a much better fit and can open the lock effortlessly. The four major Covid variants that are more infectious than the original model have refined the key they carry to more efficiently bind to the ACE-2 receptors. While no details are available the US is reporting the discovery of 10 new variants this week.
Available data suggests that the new variants are not, per se, more deadly than the original models. They are, however, far more infectious. A year ago, for example, for every 1000 SARS virions that were inhaled into our mouth 100 would actually infect us. Now we may have a situation where for every 1000 virions of the variant strain that enter our mouth, 800 may actually infect us. More infections are therefore likely to occur and that means more people who are particularly vulnerable will be infected, with an associated increase in mortality.
More infectious variants have been detected in Australia and there has been a massive and mainly successful public health response to limit viral spread. We are now in an enviable situation compared to so much of the world. However, clearly now only a successful global vaccination program can tame the pandemic.
So where are we at with vaccines?
The good news is that all the vaccines approved for use, including those produced by China and Russia, work. Some are better than others but all provide close to 100% protection from a Covid infection causing death or an illness requiring hospitalisation. While the Pfizer vaccine appears to block all Covid related illness, other vaccines may not stop people from developing symptoms of a severe “cold”. We can live with that.
It also appears that the vaccines provide protection from the variant strains so far identified. There is a real risk that this situation could change with new variations. The world is being immunised against the original strain of SARS-Cov-2 identified a year ago. Antibodies produced in response to a vaccine based on this original form may not be as effective in the future if the leopard makes very significant changes to its spots. We will need to look carefully at the need to reformulate current vaccines.
None of the vaccines has been shown to produce ‘sterilising immunity” I.e. stop the immunised from having viable virus reside in respiratory secretions. The presence of virus in such individuals poses no dangers to them but it does not stop the immunised from infecting the non-immunised. An obvious consequence will be the need, for the foreseeable future, to quarantine arriving travellers even if they have been immunised.
The safety profile of all the vaccines is reassuring. With more than 40 million doses of vaccine administered we have seen between 5 and 11 cases of allergic reactions per million vaccinations. As is true with most vaccinations a local reaction, sometimes associated with fever and fatigue that lasts a few days, is not uncommon after a second injection.
Unfortunately many anti-vaccination sites contain stories of severe complications. Any adverse event in the weeks after vaccination is documented and analysed by researchers. Given the millions of vaccinations and the vulnerability of many vaccinated older individuals from pre-existing co-morbidities, co-incidental problems in the weeks following vaccination are to be expected. Many anti-vaccination websites are using these to falsely claim that the vaccines are dangerous.
What don’t we know?
We anticipate but don’t know that immunity following vaccination will last at least six months. We will soon learn if annual vaccination will be required as with the influenza vaccine. We don’t know if those who have recovered from a Covid illness require vaccination but we are presuming that a booster shot would be a good idea. We need to know if it is safe to immunise children. There is no reason to expect that this should be a problem and we do know that immunising kids who are good viral spreaders would be desirable.
So the race is on. To end the pandemic we need a huge proportion of the human family to be immunised in a relatively short period. If vaccination efforts are prolonged immunity may wan before their chances of meeting up with the virus again are eliminated. History will judge us harshly if we allow local selfish imperatives to dominate the vaccination program for the world.
China’s ‘silk diplomacy’, with its supply of vaccines to poor countries, is much appreciated. All of us ‘haves’ need to act similarly. By promoting global equity we are supporting initiatives essential for our own self-protection. And in this hoped-for success we will realise how similar rather than different we all are.