More than a dozen Covid vaccines are in development, with many of them already being tested in humans and many more to begin human trials soon. But what do we actually know about these potential vaccines and why might we be wary of them? Wary, of course, does not mean we stop testing them, but it does mean we must be careful, to fully understand what they do, what they don’t do, and what harm they might cause to otherwise healthy adults and children.
First, what don’t we know?
We do not know if they are safe. No human safety data is available to the public as far as I am aware, though some companies have issued press releases claiming safety without releasing the data. This is a concern as we are contemplating eventually giving vaccines to two to three billion people or more. One adverse reaction will result in many millions either injured or killed.
We don’t know if they will protect anyone from infection. Yes, they raise antibodies in experimental animals but it is still unclear whether the animals are protected.
Data from studies with a very limited number of non-human primates (monkeys) is available for one type of vaccine (an adenovirus vector that carries the spike protein gene of SARS-CoV-2). Vaccination failed to protect any of the monkeys from infection of the nasal but did lower the amount of virus as virus-associated damage to the lung. Similar results were found for experimental SARS and MERS vaccines. Extrapolation of the degree protection of the lung from monkey to human is difficult as SARS-CoV-2 does not cause serious disease in these animals.
The failure to protect animals from nasal infection raises the possibility that vaccines will offer only partial protection, that is, they may reduce lung disease but not infection via the nasal mucosa, the primary route through which the virus enters the human body. Will such partial protection prevent SARS-CoV-2 disease?
The experience with SARS-CoV-2 in children offers some insight. Most children infected by SARS-CoV-2 exhibit mild symptoms. Some may have a fever and cold-like symptoms. Few experience lung disease. Childhood resistance is likely the consequence of more active immune defenses, as compared to those 25 and older, and of a much lower concentration of the ACE-2 virus receptor in the lungs of children as compared to adults. Recent measures showed an increase in the density of ACE-2 on type II lung pneumocystis with age. That means very little virus is found in children’s lungs, similar to what was seen in the vaccinated monkeys.
We now know the absence of lung disease in children does not mean that all are spared the life-threatening consequences of SARS-CoV-2 infection. A new syndrome, Multisystem Inflammatory Syndrome-Children (MIS-C), is now recognized to be a late consequence of SARS-CoV-2 in children ages zero to twenty. MIS-C is characterized by generalized inflammation of the vascular system, inflammation of the heart (myocarditis)and aneurysms (ballooning of the vessels). Clotting abnormalities, often present in severely ill Covid-19 adults, may also occur among children.
Children teach us that partially effective vaccines which spare the lung may not spare vaccinated adults (or children) from illness and death. This is all the more reason to proceed cautiously with Covid-19 vaccines. The rush to approval may endanger many more lives than does the disease itself.